BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting... more BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting authors, nonprofit publishers, academic institutions, research libraries, and research funders in the common goal of maximizing access to critical research. BioOne (www.bioone.org) is a nonprofit, online aggregation of core research in the biological, ecological, and environmental sciences. BioOne provides a sustainable online platform for over 170 journals and books published by nonprofit societies, associations, museums, institutions, and presses.
Understanding the ranging behaviours of species can be helpful in effective conservation planning... more Understanding the ranging behaviours of species can be helpful in effective conservation planning. However, for many species that are rare, occur at low densities, or occupy challenging environments, this information is often lacking. The Martial Eagle (Polemaetus belli-cosus) is a low density apex predator declining in both non-protected and protected areas in southern Africa, and little is known about its ranging behaviour. We use GPS tags fitted to Martial Eagles (n = 8) in Kruger National Park (KNP), South Africa to describe their ranging behaviour and habitat preference. This represents the first time that such movements have been quantified in adult Martial Eagles. Territorial eagles (n = 6) held home ranges averaging ca. 108 km 2. Home range estimates were similar to expectations based on inter-nest distances , and these large home range sizes could constrain the carrying capacity of even the largest conservation areas. Two tagged individuals classed as adults on plumage apparently did not hold a territory, and accordingly ranged more widely (ca. 44,000 km 2), and beyond KNP boundaries as floaters. Another two territorial individuals abandoned their territories and joined the 'floater' population, and so ranged widely after leaving their territories. These unexpected movements after territory abandonment could indicate underlying environmental degradation. Relatively high mortality of these wide-ranging 'floaters' due to anthropogenic causes (three of four) raises further concerns for the species' persistence. Habitat preference models suggested Martial Eagles used areas preferentially that were closer to rivers, had higher tree cover, and were classed as dense bush rather than open bush or grassland. These results can be used by conservation managers to help guide actions to preserve breeding Martial Eagles at an appropriate spatial scale.
How multiple morphs are maintained within populations of colour polymorphic bird species remains ... more How multiple morphs are maintained within populations of colour polymorphic bird species remains a challenging question in evolutionary ecology. In some systems, differential productivity or survival between morphs are thought to play a role. Here we examine key demographic parameters between the two discrete adult morphs that characterise the polymorphic black sparrowhawk Accipiter melanoleucus. Using long-term breeding and survival data from a population on the Cape Peninsula, South Africa, we test for differences in reproductive performance between light and dark morphs, both in isolation and in combination with their partner morph and adult survival between morphs. We found that neither morph had a specific advantage in terms of productivity or survival. Despite this lack of difference between the individual morphs, we did however find that morph combination of adult pairs influenced productivity significantly, with mixed-pairs producing more offspring per year than pairs consisting of the same morph. The body condition of the offspring showed the opposite relationship, with nestlings of mixed-pairs having lower body condition than nestlings of like-pairs. While our results suggest an advantage of mating with the opposite morph, there was no evidence for disassortative mating; instead breeding pair morph combinations were random with respect to the background frequencies of the two morphs. Higher productivity of mixed-pairs may be the result of the complementary nature of care provided by the different morphs. We propose that differential foraging success between black sparrowhawk morphs under varying light conditions allows mixed-pairs to expand their foraging niche. We conclude that emergent pair-level properties may play an important role in promoting and maintaining polymorphism and may be important for other bird species which display bi-parental care.
Detectability of different colour morphs under varying light conditions has been proposed as an i... more Detectability of different colour morphs under varying light conditions has been proposed as an important driver in the maintenance of colour polymorphism via disruptive selection. To date, no studies have tested whether different morphs have selective advantages under differing light conditions. We tested this hypothesis in the black sparrowhawk, a polymorphic raptor exhibiting a discrete white and dark morph, and found that prey provisioning rates differ between the morphs depending on light condition. Dark morphs delivered more prey in lower light conditions, while white morphs provided more prey in brighter conditions. We found support for the role of breeding season light level in explaining the clinal pattern of variation in morph ratio across the species range throughout South Africa. Our results provide the first empirical evidence supporting the hypothesis that polymorphism in a species, and the spatial structuring of morphs across its distribution , may be driven by differential selective advantage via improved crypsis, under varying light conditions.
As the global trend towards urbanization continues, the need to understand its impact on wildlife... more As the global trend towards urbanization continues, the need to understand its impact on wildlife grows. Species may have different levels of tolerance to urban disturbance; some even appear to thrive in urban areas and use human-subsidized resources. However, the physiological costs and trade-offs faced by urban-dwelling species are still poorly understood. We assess the evidence for a negative impact of urbanization on the Black Spar-rowhawk Accipiter melanoleucus, a raptor that recently colonized Cape Town, South Africa, and explore the potential mechanisms behind any such effect. We predicted that birds in more urbanized areas may be in poorer health and that this may be partially driven by differences in prey quantity and quality along an urban habitat gradient. The health of Black Sparrowhawk nestlings was evaluated through measures of their physiological stress (heterophil/lymphocyte ratio), body condition and blood parasite infection (infection risk and intensity of Haemoproteus and Leucocytozoon). Diet composition was determined through an analysis of prey remains collected around nests, and prey abundance was determined through point counts in different habitat types. We could find no negative effects of urbanization on nestling health, with no significant relationships with heterophil/lymphocyte ratio, body condition, risk and intensity of infection by Haemopro-teus or intensity of infection by Leucocytozoon. Risk of infection by Leucocytozoon did, however , decline with increasing urban cover, perhaps because urbanized areas contain less habitat for blackflies, the vectors of this parasite, which require moving fresh water. We found no change in diet breadth or composition with increasing urban cover. Although some prey species were abundant or less abundant in certain habitat types, all habitat types contained ample prey for Black Sparrowhawks. The widespread abundance of food resources and resulting lack of nutritional stress may explain why Black Sparrowhawks are seemingly free of the negative health impacts expected to arise from urbanization. These findings may explain the success of the species in Cape Town and suggest that for urban-dwelling, bird-eating raptors the abundance of prey in cities may override any potential negative impacts of urbanization on health due to disturbance or other sources of stress.
1. From an evolutionary perspective, recruitment into the breeding population represents one of t... more 1. From an evolutionary perspective, recruitment into the breeding population represents one of the most important life-history stages and ultimately determines the effective population size. In order to contribute to the next generation, offspring must survive to sexual maturity, secure a territory and find a mate. 2. In this study, we explore factors influencing both offspring survival and their subsequent recruitment into the local breeding population in a long-lived urban raptor, the black sparrowhawk (Accipiter melanoleucus). Adult black sparrowhawks show discrete colour poly-morphism (dark and light morphs), and in South Africa, morphs are distributed clinally with the highest proportion of dark morphs (c.75%) present in our study population on the Cape Peninsula. 3. Parental morph was associated with both survival and recruitment. For survival, parental morph combination was important – with young produced by pairs of contrasting morphs having higher survival rates than young fledged from like-pairs. The association between recruitment and morph was more complex; with an interaction between male morph and breeding time, whereby recruitment of offspring from dark morph fathers was more likely when fledging earlier in the season. The opposite relationship was found for light morph fathers, with their offspring more likely to be recruited if fledged later in the season. 4. This interaction may be due to differential morph-specific hunting success of fathers (males contribute most food provisioning), linked to background matching and crypsis in different weather conditions. Dark morph males may hunt more successfully in rainier and cloudier conditions, which occur more frequently earlier in the breeding season, and light morph males may be more successful later on, when weather conditions become increasingly brighter and drier. Our results reveal a complex situation whereby the family morph combination influences survival, and the father morphs specifically recruitment, revealing morph-specific benefits dependent on the timing of breeding. These empirical data are among the first to support the idea that differential fitness consequence of morph combination may explain balanced polymorphism in a vertebrate population.
Background: Black sparrowhawks (Accipiter melanoleucus) recently colonised the Cape Peninsula, So... more Background: Black sparrowhawks (Accipiter melanoleucus) recently colonised the Cape Peninsula, South Africa, where the species faces competition for their nest sites from Egyptian geese (Alopochen aegyptiaca) which frequently usurp black sparrowhawk nests. In this paper, we test the hypothesis that multiple nest building by black sparrowhawks is a strategy to cope with this competitor, based on a 14-year long term data set.
Urban Black Sparrowhawk males hunt mostly within 2.27 km of their nest during the
breeding season... more Urban Black Sparrowhawk males hunt mostly within 2.27 km of their nest during the breeding season (‘home range’ of 16.15 km2) and increased the distance slightly to 2.43 km outside of the breeding season (18.56 km2). We found high individual variation within and between six global positioning systems tagged breeding males, but no significant seasonal differences in the urban environment of Cape Town, South Africa.
Specialist predators are generally negatively impacted by habitat change. Predators that inhabit ... more Specialist predators are generally negatively impacted by habitat change. Predators that inhabit transformed areas are usually forced to diversify their diet and this departure away from traditional resources can have negative consequences for fitness and demographic parameters. We consider this relationship as it applies to Verreaux's eagles Aquila verreauxii, which is typically considered to be a highly specialised predator of hyraxes (Procavia and Heterohyrax spp.). We investigate diet in relation to land cover in two adjacent areas of South Africa and explore the links between diet diversity, the percentage of hyrax consumed, and the breeding performance of eagles. We also examine these same patterns using data from other studies. We found that diet diversity was greater in the agriculturally developed Sandveld region compared to the natural Cederberg region. Proportions of the three main prey types were correlated with the proportion of agriculturally developed land around the nest site. Breeding performance was correlated with the diet, but not in the manner expected, with breeding productivity being greater in regions with large diet diversity and a small proportion of hyrax in the diet. We found similar patterns when placing our results into a broader geographical context using other dietary studies of Verreaux's eagles, suggesting our results were not unique to our study system. Thus, our results suggest that diet diversification does not necessarily impinge on breeding performance in the presence of adequate alternative prey resources. This research adds to the growing number of studies suggesting that some predators may be adaptable up to a threshold level of habitat transformation. These results have implications for predicting changes on such species by anthropogenic habitat transformation and highlight the potential for agriculturally developed areas to maintain a conservation value when habitat heterogeneity is maintained.
Information on movement ecology is key in understanding the drivers and limitations of life histo... more Information on movement ecology is key in understanding the drivers and limitations of life history traits and has a potential role in indicating environmental change. Currently we have a limited understanding of the parameters of movement of territory-bound raptors, which are sensitive to environmental change. In this study we used GPS tracking technology to obtain spatially (within 3 m) and temporally (c. 3 mins) high-resolution movement data on a small sample of Verreaux's eagle Aquila verreauxii during the pre-laying period (n = 4) with one additional example during the chick rearing period. We present GPS-derived home range estimates for this species and we examine temporal (timing, duration, frequency and speed) and spatial (total path length and maximum distance from nest) patterns of trips away from the nest. For eagles tagged in the agriculturally developed Sandveld region (n = 3), which is made up of a mosaic of land use types, we also undertook a habitat selection analysis. Home ranges were small and largely mutually exclusive. Trip activity was centred around midday, which is likely to be related to lift availability. Our habitat selection analysis found that eagles selected for near-natural and degraded habitat over natural or completely modified areas, suggesting that these eagles may have benefitted from some of the agricultural development in this region. Although our sample sizes are small, the resolution of our tracking data was essential in deriving this data over a relatively short time period and paves the way for future research.
Breeding productivity frequently shows variation across a species' range or locally between diffe... more Breeding productivity frequently shows variation across a species' range or locally between different habitat types. Agricultural transformation generally has negative effects on biodiversity and often results in reduced prey abundance or increased foraging effort in top predators and, consequently, often reduces breeding productivity. Major factors that affect reproductive success also include climatic variables, breeding density, and timing of breeding. We explored the influence of agricultural transformation on a specialist raptor, Verreaux's Eagle (Aquila verreauxii). From 2011 to 2014, we examined productivity in 2 adjacent populations in the Western Cape Province, South Africa: an unspoiled area of Fynbos vegetation with little human development (the Cederberg Mountains) and an agriculturally transformed area (the Sandveld region). Counterintuitively, breeding productivity was higher in the agricultural than in the natural site. In particular, the proportion of pairs that attempted to breed (i.e. breeding rate) was higher in the Sandveld (0.94 6 0.07 attempts pair À1 yr À1) than in the Cederberg (0.48 6 0.14 attempts pair À1 yr À1). Nesting success was also higher in the Sandveld (0.80 6 0.05 fledged young attempt À1 yr À1) than in the Cederberg (0.57 6 0.13 fledged young attempt À1 yr À1), and the probability of nesting successfully was related to the lay date (decreased success with later laying) and to the total cumulative rainfall up to 28 days after hatching (decreased success with increasing rainfall). Using the site-specific breeding rates to produce a population model, we found that in isolation, the Cederberg population is unlikely to be self-sustaining, but Verreaux's Eagles breeding in the agriculturally developed Sandveld region are likely to be an important source population, despite occurring at a much lower density. These results, contrary to our expectations, suggest that Verreaux's Eagle may be more adaptable to agricultural transformation than previously thought, with breeding performance in the agricultural site adequate to maintain the population.
1. Describing spatial patterns of phenotypic traits can be important for evolutionary and ecologi... more 1. Describing spatial patterns of phenotypic traits can be important for evolutionary and ecological studies. However, traditional approaches, such as fieldwork, can be time-consuming and expensive. Information technologies , such as Internet search engines, could facilitate the collection of these data. Google Images is one such technology that might offer an opportunity to rapidly collect information on spatial patterns of phenotypic traits. 2. We investigated the use of Google Images in extracting data on geographical variation in phenotypic traits visible from photographs. We compared the distribution of visual traits obtained from Google Images with four previous studies: colour morphs of black bear (Ursus americanus); colouration and spottiness in barn owl (Tyto alba); colour morphs of black sparrowhawk (Accipiter melanoleucus) and the distribution of hooded (Corvus cor-one) and carrion crows (Corvus cornix) across their European hybrid zone. Additionally, we develop and present a web application (MORPHIC), which facilitates the human data capture process of this method. 3. We found good agreement between fieldwork data and Google Images data across all studies. Indeed, there was strong agreement between the data obtained from the original study and from the Google Images method for the colour morphs of black bear (R 2 = 80%) and for two barn owl plumage traits (R 2 = 64% and 53%). Our approach also successfully matched the clinal variation of black sparrowhawks morphs across South Africa. Our method also gave a good agreement between the distribution of hooded and carrion crows (with 86% placed on the correct side of the hybrid zone line). 4. Our results suggest that this method can work well for visible traits of common and widespread species that are objective, binary, and easy to see irrespective of angle. The Google Images method is cost-effective and rapid and can be used with some confidence when investigating patterns of geographical variation, as well as a range of other applications. In many cases, it could therefore supplement or replace fieldwork.
Capsule: Fledglings progressively increase their home range size and ranging behaviour as they
ag... more Capsule: Fledglings progressively increase their home range size and ranging behaviour as they age. Aims: To examine the home range size and ranging behaviour of Bearded Vulture fledglings during the post-fledging dependence period and determine the onset of natal dispersal. Methods: Post-fledging movements of three individuals were investigated in southern Africa using global positioning system (GPS) satellite telemetry which enabled home range sizes and distances travelled from the nest to be calculated. Results: Fledglings increased their home range size from an average of 0.4–10 999 km2 (100% Minimum Convex Polygons) and 9.13–11 466 km2 (fixed 95% kernels) within the first six months post fledging. They also increased home range use as they aged with maximum daily distances travelled from the nest occurring between 98 and 136 days post fledging (when fledglings were aged between 222 and 262 days), after which time they dispersed from their natal area. Distances between fixes were highest during the dispersal period. Conclusion: GPS satellite telemetry allows us to accurately demonstrate how fledglings progressively increase and use their home ranges as they age and undertake pre-dispersive exploratory flights. Results confirm the notion that juveniles disperse at the onset of the following breeding season and suggest that dispersal occurs earlier in the southern hemisphere.
Reply to comment on: Vegetation burning for game management in the UK uplands is increasing and o... more Reply to comment on: Vegetation burning for game management in the UK uplands is increasing and overlaps spatially with soil carbon and protected areas In their comment, Davies et al. (2015) question the use of MODIS to assess temporal changes in prescribed burning for grouse management, stating that MODIS " cannot detect " such burns because the fires are too small. This is incorrect. MODIS can detect fires of ~100 m 2 with ≥50% probability, and can detect fires as small as 50 m 2 (https://earthdata. nasa.gov/files/MODIS_Fire_Users_Guide_2.5.pdf). Thus, fire fronts ranging from 1 to 3 m wide and length of ~100 m and ~33 m respectively would have ≥ 50% detection probability. We randomly selected 10 1-km squares from our study area which had ≥ 50% moorland and ≥5% burning, obtained a Google Earth image of each square and measured all visible burns in a random 250 × 250 m quadrant per square. Of these burns (n = 206), 40% were ≥100 m and 92% were ≥33 m length. Thus, MODIS data can be used to provide an index of prescribed burning activity. Detection rates are low, but fire size is not the only factor leading to a fire remaining undetected by MODIS. Other influences include cloud, smoke levels, homogeneity of land surface, angle and/or time of satellite pass and fire intensity (https://earthdata.nasa.gov/files/MODIS_Fire_ Users_Guide_2.5.pdf). The fact that, despite these influences MODIS provides a useful index of burning activity is illustrated in Fig. 1, where MODIS detections within our study area show a clear correspondence with the permissible burning period. Burns are recorded from 1 October and end abruptly after 30 April, consistent with the burning season which runs from 1 October to 15 April, extending to 30 April in Scotland subject to landowner permission. Wildfires would not be expected to show these abrupt seasonal patterns except insofar as some of them may arise from escaped prescribed burns. The scattering of fires in summer will be wildfires. Lastly, the percentage area of burning determined from our visual assessments was twice as high on squares where MODIS detected at least one burn compared to those where no burns were detected (9.9 ± 0.1% vs 4.1 ± 0.1%; F 2,34,101 = 320.4, P b 0.0001). These figures were based on analysis comparing visual burn extent on all our assessed squares containing moorland (n = 34,104), split by presence or absence of one or more MODIS fires, using a GLM with percentage area of burning from imagery as the logit-transformed response per square, MODIS burns as a binary fixed effect and a covariate of percentage area of moorland. Davies et al. (2015) suggest that the plotted relationship in Fig. 5 of Douglas et al. (2015) is noisy, estimating an r 2 (adj) of 0.32. The correct calculation for this over-dispersed Poisson model gives R 2 D,γD = 0.40, which is sufficient to have confidence in the relationship. A ten-year period is more than adequate to estimate a trend in a dataset, and a significant trend over this period is evidence of real change in the number of detected burns. A non-linear fitted relationship is expected for Poisson regression, reflecting the prediction of fitted values on the log scale. The removal of two statistically significant outlier years was one of several steps taken to minimize the inclusion of wildfires in our MODIS dataset and is an accepted procedure
Repeat monitoring is vital to measure biodiversity change. However, monitoring protocols may chan... more Repeat monitoring is vital to measure biodiversity change. However, monitoring protocols may change, as survey techniques improve or different questions are asked. Such modifications may cause difficulties when examining changes in wildlife populations. The Southern African Bird Atlas Project (SABAP) 1 and 2 are repeat national bird surveys undertaken 20 years apart. These surveys therefore offer unrivalled potential to examine bird population changes in an African context. However, changes in protocols, both spatially and temporally, between the two surveys have raised concerns over using these data to infer population changes. In this study we use independ-ent nest survey data to test whether changes in reporting rates of Martial Eagles in the Kalahari Gemsbok National Park between the two SABAP surveys were reflected in real change in numbers of nesting pairs. From 11 quarter degree squares (QDS), covering c. 8 000 km2, both SABAP and nest surveys suggested a near identical 44% decline. Levels of agreement were weaker at the individual QDS scale, although in 67% of cases the direction of change was the same using both surveys. These results suggest that comparisons in the reporting rates between SABAP 1 and SABAP 2 accurately reflect changes in the breeding population size of this species.
Bearded Vulture Gypaetus barbatus movements were investigated in southern Africa to determine whe... more Bearded Vulture Gypaetus barbatus movements were investigated in southern Africa to determine whether an individual's age, sex or breeding status influenced its ranging behaviour and to provide the information required to guide conservation activities. Data from satellite transmitters fitted to 18 individuals of four age classes were used to determine range size and use. Because of the nature of the movements of marked individuals, these data could be used to determine the overall foraging range of the entire population, which was estimated to be 51 767 km(2). Although juvenile, immature and sub-adult birds used different parts of the overall range, their combined foraging range was 65% (33 636 km(2)) of the overall range. Average adult home ranges (286 km(2)) were only around 1% the size of the average foraging ranges of non-adults (10 540 -25 985 km(2)), with those of breeding adults being even smaller (95 km(2)). Home ranges of breeding adults did not vary in size between sea...
BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting... more BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting authors, nonprofit publishers, academic institutions, research libraries, and research funders in the common goal of maximizing access to critical research. BioOne (www.bioone.org) is a nonprofit, online aggregation of core research in the biological, ecological, and environmental sciences. BioOne provides a sustainable online platform for over 170 journals and books published by nonprofit societies, associations, museums, institutions, and presses.
Understanding the ranging behaviours of species can be helpful in effective conservation planning... more Understanding the ranging behaviours of species can be helpful in effective conservation planning. However, for many species that are rare, occur at low densities, or occupy challenging environments, this information is often lacking. The Martial Eagle (Polemaetus belli-cosus) is a low density apex predator declining in both non-protected and protected areas in southern Africa, and little is known about its ranging behaviour. We use GPS tags fitted to Martial Eagles (n = 8) in Kruger National Park (KNP), South Africa to describe their ranging behaviour and habitat preference. This represents the first time that such movements have been quantified in adult Martial Eagles. Territorial eagles (n = 6) held home ranges averaging ca. 108 km 2. Home range estimates were similar to expectations based on inter-nest distances , and these large home range sizes could constrain the carrying capacity of even the largest conservation areas. Two tagged individuals classed as adults on plumage apparently did not hold a territory, and accordingly ranged more widely (ca. 44,000 km 2), and beyond KNP boundaries as floaters. Another two territorial individuals abandoned their territories and joined the 'floater' population, and so ranged widely after leaving their territories. These unexpected movements after territory abandonment could indicate underlying environmental degradation. Relatively high mortality of these wide-ranging 'floaters' due to anthropogenic causes (three of four) raises further concerns for the species' persistence. Habitat preference models suggested Martial Eagles used areas preferentially that were closer to rivers, had higher tree cover, and were classed as dense bush rather than open bush or grassland. These results can be used by conservation managers to help guide actions to preserve breeding Martial Eagles at an appropriate spatial scale.
How multiple morphs are maintained within populations of colour polymorphic bird species remains ... more How multiple morphs are maintained within populations of colour polymorphic bird species remains a challenging question in evolutionary ecology. In some systems, differential productivity or survival between morphs are thought to play a role. Here we examine key demographic parameters between the two discrete adult morphs that characterise the polymorphic black sparrowhawk Accipiter melanoleucus. Using long-term breeding and survival data from a population on the Cape Peninsula, South Africa, we test for differences in reproductive performance between light and dark morphs, both in isolation and in combination with their partner morph and adult survival between morphs. We found that neither morph had a specific advantage in terms of productivity or survival. Despite this lack of difference between the individual morphs, we did however find that morph combination of adult pairs influenced productivity significantly, with mixed-pairs producing more offspring per year than pairs consisting of the same morph. The body condition of the offspring showed the opposite relationship, with nestlings of mixed-pairs having lower body condition than nestlings of like-pairs. While our results suggest an advantage of mating with the opposite morph, there was no evidence for disassortative mating; instead breeding pair morph combinations were random with respect to the background frequencies of the two morphs. Higher productivity of mixed-pairs may be the result of the complementary nature of care provided by the different morphs. We propose that differential foraging success between black sparrowhawk morphs under varying light conditions allows mixed-pairs to expand their foraging niche. We conclude that emergent pair-level properties may play an important role in promoting and maintaining polymorphism and may be important for other bird species which display bi-parental care.
Detectability of different colour morphs under varying light conditions has been proposed as an i... more Detectability of different colour morphs under varying light conditions has been proposed as an important driver in the maintenance of colour polymorphism via disruptive selection. To date, no studies have tested whether different morphs have selective advantages under differing light conditions. We tested this hypothesis in the black sparrowhawk, a polymorphic raptor exhibiting a discrete white and dark morph, and found that prey provisioning rates differ between the morphs depending on light condition. Dark morphs delivered more prey in lower light conditions, while white morphs provided more prey in brighter conditions. We found support for the role of breeding season light level in explaining the clinal pattern of variation in morph ratio across the species range throughout South Africa. Our results provide the first empirical evidence supporting the hypothesis that polymorphism in a species, and the spatial structuring of morphs across its distribution , may be driven by differential selective advantage via improved crypsis, under varying light conditions.
As the global trend towards urbanization continues, the need to understand its impact on wildlife... more As the global trend towards urbanization continues, the need to understand its impact on wildlife grows. Species may have different levels of tolerance to urban disturbance; some even appear to thrive in urban areas and use human-subsidized resources. However, the physiological costs and trade-offs faced by urban-dwelling species are still poorly understood. We assess the evidence for a negative impact of urbanization on the Black Spar-rowhawk Accipiter melanoleucus, a raptor that recently colonized Cape Town, South Africa, and explore the potential mechanisms behind any such effect. We predicted that birds in more urbanized areas may be in poorer health and that this may be partially driven by differences in prey quantity and quality along an urban habitat gradient. The health of Black Sparrowhawk nestlings was evaluated through measures of their physiological stress (heterophil/lymphocyte ratio), body condition and blood parasite infection (infection risk and intensity of Haemoproteus and Leucocytozoon). Diet composition was determined through an analysis of prey remains collected around nests, and prey abundance was determined through point counts in different habitat types. We could find no negative effects of urbanization on nestling health, with no significant relationships with heterophil/lymphocyte ratio, body condition, risk and intensity of infection by Haemopro-teus or intensity of infection by Leucocytozoon. Risk of infection by Leucocytozoon did, however , decline with increasing urban cover, perhaps because urbanized areas contain less habitat for blackflies, the vectors of this parasite, which require moving fresh water. We found no change in diet breadth or composition with increasing urban cover. Although some prey species were abundant or less abundant in certain habitat types, all habitat types contained ample prey for Black Sparrowhawks. The widespread abundance of food resources and resulting lack of nutritional stress may explain why Black Sparrowhawks are seemingly free of the negative health impacts expected to arise from urbanization. These findings may explain the success of the species in Cape Town and suggest that for urban-dwelling, bird-eating raptors the abundance of prey in cities may override any potential negative impacts of urbanization on health due to disturbance or other sources of stress.
1. From an evolutionary perspective, recruitment into the breeding population represents one of t... more 1. From an evolutionary perspective, recruitment into the breeding population represents one of the most important life-history stages and ultimately determines the effective population size. In order to contribute to the next generation, offspring must survive to sexual maturity, secure a territory and find a mate. 2. In this study, we explore factors influencing both offspring survival and their subsequent recruitment into the local breeding population in a long-lived urban raptor, the black sparrowhawk (Accipiter melanoleucus). Adult black sparrowhawks show discrete colour poly-morphism (dark and light morphs), and in South Africa, morphs are distributed clinally with the highest proportion of dark morphs (c.75%) present in our study population on the Cape Peninsula. 3. Parental morph was associated with both survival and recruitment. For survival, parental morph combination was important – with young produced by pairs of contrasting morphs having higher survival rates than young fledged from like-pairs. The association between recruitment and morph was more complex; with an interaction between male morph and breeding time, whereby recruitment of offspring from dark morph fathers was more likely when fledging earlier in the season. The opposite relationship was found for light morph fathers, with their offspring more likely to be recruited if fledged later in the season. 4. This interaction may be due to differential morph-specific hunting success of fathers (males contribute most food provisioning), linked to background matching and crypsis in different weather conditions. Dark morph males may hunt more successfully in rainier and cloudier conditions, which occur more frequently earlier in the breeding season, and light morph males may be more successful later on, when weather conditions become increasingly brighter and drier. Our results reveal a complex situation whereby the family morph combination influences survival, and the father morphs specifically recruitment, revealing morph-specific benefits dependent on the timing of breeding. These empirical data are among the first to support the idea that differential fitness consequence of morph combination may explain balanced polymorphism in a vertebrate population.
Background: Black sparrowhawks (Accipiter melanoleucus) recently colonised the Cape Peninsula, So... more Background: Black sparrowhawks (Accipiter melanoleucus) recently colonised the Cape Peninsula, South Africa, where the species faces competition for their nest sites from Egyptian geese (Alopochen aegyptiaca) which frequently usurp black sparrowhawk nests. In this paper, we test the hypothesis that multiple nest building by black sparrowhawks is a strategy to cope with this competitor, based on a 14-year long term data set.
Urban Black Sparrowhawk males hunt mostly within 2.27 km of their nest during the
breeding season... more Urban Black Sparrowhawk males hunt mostly within 2.27 km of their nest during the breeding season (‘home range’ of 16.15 km2) and increased the distance slightly to 2.43 km outside of the breeding season (18.56 km2). We found high individual variation within and between six global positioning systems tagged breeding males, but no significant seasonal differences in the urban environment of Cape Town, South Africa.
Specialist predators are generally negatively impacted by habitat change. Predators that inhabit ... more Specialist predators are generally negatively impacted by habitat change. Predators that inhabit transformed areas are usually forced to diversify their diet and this departure away from traditional resources can have negative consequences for fitness and demographic parameters. We consider this relationship as it applies to Verreaux's eagles Aquila verreauxii, which is typically considered to be a highly specialised predator of hyraxes (Procavia and Heterohyrax spp.). We investigate diet in relation to land cover in two adjacent areas of South Africa and explore the links between diet diversity, the percentage of hyrax consumed, and the breeding performance of eagles. We also examine these same patterns using data from other studies. We found that diet diversity was greater in the agriculturally developed Sandveld region compared to the natural Cederberg region. Proportions of the three main prey types were correlated with the proportion of agriculturally developed land around the nest site. Breeding performance was correlated with the diet, but not in the manner expected, with breeding productivity being greater in regions with large diet diversity and a small proportion of hyrax in the diet. We found similar patterns when placing our results into a broader geographical context using other dietary studies of Verreaux's eagles, suggesting our results were not unique to our study system. Thus, our results suggest that diet diversification does not necessarily impinge on breeding performance in the presence of adequate alternative prey resources. This research adds to the growing number of studies suggesting that some predators may be adaptable up to a threshold level of habitat transformation. These results have implications for predicting changes on such species by anthropogenic habitat transformation and highlight the potential for agriculturally developed areas to maintain a conservation value when habitat heterogeneity is maintained.
Information on movement ecology is key in understanding the drivers and limitations of life histo... more Information on movement ecology is key in understanding the drivers and limitations of life history traits and has a potential role in indicating environmental change. Currently we have a limited understanding of the parameters of movement of territory-bound raptors, which are sensitive to environmental change. In this study we used GPS tracking technology to obtain spatially (within 3 m) and temporally (c. 3 mins) high-resolution movement data on a small sample of Verreaux's eagle Aquila verreauxii during the pre-laying period (n = 4) with one additional example during the chick rearing period. We present GPS-derived home range estimates for this species and we examine temporal (timing, duration, frequency and speed) and spatial (total path length and maximum distance from nest) patterns of trips away from the nest. For eagles tagged in the agriculturally developed Sandveld region (n = 3), which is made up of a mosaic of land use types, we also undertook a habitat selection analysis. Home ranges were small and largely mutually exclusive. Trip activity was centred around midday, which is likely to be related to lift availability. Our habitat selection analysis found that eagles selected for near-natural and degraded habitat over natural or completely modified areas, suggesting that these eagles may have benefitted from some of the agricultural development in this region. Although our sample sizes are small, the resolution of our tracking data was essential in deriving this data over a relatively short time period and paves the way for future research.
Breeding productivity frequently shows variation across a species' range or locally between diffe... more Breeding productivity frequently shows variation across a species' range or locally between different habitat types. Agricultural transformation generally has negative effects on biodiversity and often results in reduced prey abundance or increased foraging effort in top predators and, consequently, often reduces breeding productivity. Major factors that affect reproductive success also include climatic variables, breeding density, and timing of breeding. We explored the influence of agricultural transformation on a specialist raptor, Verreaux's Eagle (Aquila verreauxii). From 2011 to 2014, we examined productivity in 2 adjacent populations in the Western Cape Province, South Africa: an unspoiled area of Fynbos vegetation with little human development (the Cederberg Mountains) and an agriculturally transformed area (the Sandveld region). Counterintuitively, breeding productivity was higher in the agricultural than in the natural site. In particular, the proportion of pairs that attempted to breed (i.e. breeding rate) was higher in the Sandveld (0.94 6 0.07 attempts pair À1 yr À1) than in the Cederberg (0.48 6 0.14 attempts pair À1 yr À1). Nesting success was also higher in the Sandveld (0.80 6 0.05 fledged young attempt À1 yr À1) than in the Cederberg (0.57 6 0.13 fledged young attempt À1 yr À1), and the probability of nesting successfully was related to the lay date (decreased success with later laying) and to the total cumulative rainfall up to 28 days after hatching (decreased success with increasing rainfall). Using the site-specific breeding rates to produce a population model, we found that in isolation, the Cederberg population is unlikely to be self-sustaining, but Verreaux's Eagles breeding in the agriculturally developed Sandveld region are likely to be an important source population, despite occurring at a much lower density. These results, contrary to our expectations, suggest that Verreaux's Eagle may be more adaptable to agricultural transformation than previously thought, with breeding performance in the agricultural site adequate to maintain the population.
1. Describing spatial patterns of phenotypic traits can be important for evolutionary and ecologi... more 1. Describing spatial patterns of phenotypic traits can be important for evolutionary and ecological studies. However, traditional approaches, such as fieldwork, can be time-consuming and expensive. Information technologies , such as Internet search engines, could facilitate the collection of these data. Google Images is one such technology that might offer an opportunity to rapidly collect information on spatial patterns of phenotypic traits. 2. We investigated the use of Google Images in extracting data on geographical variation in phenotypic traits visible from photographs. We compared the distribution of visual traits obtained from Google Images with four previous studies: colour morphs of black bear (Ursus americanus); colouration and spottiness in barn owl (Tyto alba); colour morphs of black sparrowhawk (Accipiter melanoleucus) and the distribution of hooded (Corvus cor-one) and carrion crows (Corvus cornix) across their European hybrid zone. Additionally, we develop and present a web application (MORPHIC), which facilitates the human data capture process of this method. 3. We found good agreement between fieldwork data and Google Images data across all studies. Indeed, there was strong agreement between the data obtained from the original study and from the Google Images method for the colour morphs of black bear (R 2 = 80%) and for two barn owl plumage traits (R 2 = 64% and 53%). Our approach also successfully matched the clinal variation of black sparrowhawks morphs across South Africa. Our method also gave a good agreement between the distribution of hooded and carrion crows (with 86% placed on the correct side of the hybrid zone line). 4. Our results suggest that this method can work well for visible traits of common and widespread species that are objective, binary, and easy to see irrespective of angle. The Google Images method is cost-effective and rapid and can be used with some confidence when investigating patterns of geographical variation, as well as a range of other applications. In many cases, it could therefore supplement or replace fieldwork.
Capsule: Fledglings progressively increase their home range size and ranging behaviour as they
ag... more Capsule: Fledglings progressively increase their home range size and ranging behaviour as they age. Aims: To examine the home range size and ranging behaviour of Bearded Vulture fledglings during the post-fledging dependence period and determine the onset of natal dispersal. Methods: Post-fledging movements of three individuals were investigated in southern Africa using global positioning system (GPS) satellite telemetry which enabled home range sizes and distances travelled from the nest to be calculated. Results: Fledglings increased their home range size from an average of 0.4–10 999 km2 (100% Minimum Convex Polygons) and 9.13–11 466 km2 (fixed 95% kernels) within the first six months post fledging. They also increased home range use as they aged with maximum daily distances travelled from the nest occurring between 98 and 136 days post fledging (when fledglings were aged between 222 and 262 days), after which time they dispersed from their natal area. Distances between fixes were highest during the dispersal period. Conclusion: GPS satellite telemetry allows us to accurately demonstrate how fledglings progressively increase and use their home ranges as they age and undertake pre-dispersive exploratory flights. Results confirm the notion that juveniles disperse at the onset of the following breeding season and suggest that dispersal occurs earlier in the southern hemisphere.
Reply to comment on: Vegetation burning for game management in the UK uplands is increasing and o... more Reply to comment on: Vegetation burning for game management in the UK uplands is increasing and overlaps spatially with soil carbon and protected areas In their comment, Davies et al. (2015) question the use of MODIS to assess temporal changes in prescribed burning for grouse management, stating that MODIS " cannot detect " such burns because the fires are too small. This is incorrect. MODIS can detect fires of ~100 m 2 with ≥50% probability, and can detect fires as small as 50 m 2 (https://earthdata. nasa.gov/files/MODIS_Fire_Users_Guide_2.5.pdf). Thus, fire fronts ranging from 1 to 3 m wide and length of ~100 m and ~33 m respectively would have ≥ 50% detection probability. We randomly selected 10 1-km squares from our study area which had ≥ 50% moorland and ≥5% burning, obtained a Google Earth image of each square and measured all visible burns in a random 250 × 250 m quadrant per square. Of these burns (n = 206), 40% were ≥100 m and 92% were ≥33 m length. Thus, MODIS data can be used to provide an index of prescribed burning activity. Detection rates are low, but fire size is not the only factor leading to a fire remaining undetected by MODIS. Other influences include cloud, smoke levels, homogeneity of land surface, angle and/or time of satellite pass and fire intensity (https://earthdata.nasa.gov/files/MODIS_Fire_ Users_Guide_2.5.pdf). The fact that, despite these influences MODIS provides a useful index of burning activity is illustrated in Fig. 1, where MODIS detections within our study area show a clear correspondence with the permissible burning period. Burns are recorded from 1 October and end abruptly after 30 April, consistent with the burning season which runs from 1 October to 15 April, extending to 30 April in Scotland subject to landowner permission. Wildfires would not be expected to show these abrupt seasonal patterns except insofar as some of them may arise from escaped prescribed burns. The scattering of fires in summer will be wildfires. Lastly, the percentage area of burning determined from our visual assessments was twice as high on squares where MODIS detected at least one burn compared to those where no burns were detected (9.9 ± 0.1% vs 4.1 ± 0.1%; F 2,34,101 = 320.4, P b 0.0001). These figures were based on analysis comparing visual burn extent on all our assessed squares containing moorland (n = 34,104), split by presence or absence of one or more MODIS fires, using a GLM with percentage area of burning from imagery as the logit-transformed response per square, MODIS burns as a binary fixed effect and a covariate of percentage area of moorland. Davies et al. (2015) suggest that the plotted relationship in Fig. 5 of Douglas et al. (2015) is noisy, estimating an r 2 (adj) of 0.32. The correct calculation for this over-dispersed Poisson model gives R 2 D,γD = 0.40, which is sufficient to have confidence in the relationship. A ten-year period is more than adequate to estimate a trend in a dataset, and a significant trend over this period is evidence of real change in the number of detected burns. A non-linear fitted relationship is expected for Poisson regression, reflecting the prediction of fitted values on the log scale. The removal of two statistically significant outlier years was one of several steps taken to minimize the inclusion of wildfires in our MODIS dataset and is an accepted procedure
Repeat monitoring is vital to measure biodiversity change. However, monitoring protocols may chan... more Repeat monitoring is vital to measure biodiversity change. However, monitoring protocols may change, as survey techniques improve or different questions are asked. Such modifications may cause difficulties when examining changes in wildlife populations. The Southern African Bird Atlas Project (SABAP) 1 and 2 are repeat national bird surveys undertaken 20 years apart. These surveys therefore offer unrivalled potential to examine bird population changes in an African context. However, changes in protocols, both spatially and temporally, between the two surveys have raised concerns over using these data to infer population changes. In this study we use independ-ent nest survey data to test whether changes in reporting rates of Martial Eagles in the Kalahari Gemsbok National Park between the two SABAP surveys were reflected in real change in numbers of nesting pairs. From 11 quarter degree squares (QDS), covering c. 8 000 km2, both SABAP and nest surveys suggested a near identical 44% decline. Levels of agreement were weaker at the individual QDS scale, although in 67% of cases the direction of change was the same using both surveys. These results suggest that comparisons in the reporting rates between SABAP 1 and SABAP 2 accurately reflect changes in the breeding population size of this species.
Bearded Vulture Gypaetus barbatus movements were investigated in southern Africa to determine whe... more Bearded Vulture Gypaetus barbatus movements were investigated in southern Africa to determine whether an individual's age, sex or breeding status influenced its ranging behaviour and to provide the information required to guide conservation activities. Data from satellite transmitters fitted to 18 individuals of four age classes were used to determine range size and use. Because of the nature of the movements of marked individuals, these data could be used to determine the overall foraging range of the entire population, which was estimated to be 51 767 km(2). Although juvenile, immature and sub-adult birds used different parts of the overall range, their combined foraging range was 65% (33 636 km(2)) of the overall range. Average adult home ranges (286 km(2)) were only around 1% the size of the average foraging ranges of non-adults (10 540 -25 985 km(2)), with those of breeding adults being even smaller (95 km(2)). Home ranges of breeding adults did not vary in size between sea...
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breeding season (‘home range’ of 16.15 km2) and increased the distance slightly to 2.43 km
outside of the breeding season (18.56 km2). We found high individual variation within and
between six global positioning systems tagged breeding males, but no significant seasonal
differences in the urban environment of Cape Town, South Africa.
age.
Aims: To examine the home range size and ranging behaviour of Bearded Vulture fledglings during
the post-fledging dependence period and determine the onset of natal dispersal.
Methods: Post-fledging movements of three individuals were investigated in southern Africa using
global positioning system (GPS) satellite telemetry which enabled home range sizes and distances
travelled from the nest to be calculated.
Results: Fledglings increased their home range size from an average of 0.4–10 999 km2 (100%
Minimum Convex Polygons) and 9.13–11 466 km2 (fixed 95% kernels) within the first six months
post fledging. They also increased home range use as they aged with maximum daily distances
travelled from the nest occurring between 98 and 136 days post fledging (when fledglings were
aged between 222 and 262 days), after which time they dispersed from their natal area.
Distances between fixes were highest during the dispersal period.
Conclusion: GPS satellite telemetry allows us to accurately demonstrate how fledglings
progressively increase and use their home ranges as they age and undertake pre-dispersive
exploratory flights. Results confirm the notion that juveniles disperse at the onset of the
following breeding season and suggest that dispersal occurs earlier in the southern hemisphere.
breeding season (‘home range’ of 16.15 km2) and increased the distance slightly to 2.43 km
outside of the breeding season (18.56 km2). We found high individual variation within and
between six global positioning systems tagged breeding males, but no significant seasonal
differences in the urban environment of Cape Town, South Africa.
age.
Aims: To examine the home range size and ranging behaviour of Bearded Vulture fledglings during
the post-fledging dependence period and determine the onset of natal dispersal.
Methods: Post-fledging movements of three individuals were investigated in southern Africa using
global positioning system (GPS) satellite telemetry which enabled home range sizes and distances
travelled from the nest to be calculated.
Results: Fledglings increased their home range size from an average of 0.4–10 999 km2 (100%
Minimum Convex Polygons) and 9.13–11 466 km2 (fixed 95% kernels) within the first six months
post fledging. They also increased home range use as they aged with maximum daily distances
travelled from the nest occurring between 98 and 136 days post fledging (when fledglings were
aged between 222 and 262 days), after which time they dispersed from their natal area.
Distances between fixes were highest during the dispersal period.
Conclusion: GPS satellite telemetry allows us to accurately demonstrate how fledglings
progressively increase and use their home ranges as they age and undertake pre-dispersive
exploratory flights. Results confirm the notion that juveniles disperse at the onset of the
following breeding season and suggest that dispersal occurs earlier in the southern hemisphere.