C. Both

... 24th International Ornithological Congress, Hamburg, Germany, 13-19 August 2006 68 ... Verhulst S, Salomons M, Mulder E, van de Zande L Telomere length in Jackdaws in relation to age, reproduction and survival University of Groningen, Behavioral Biology Group, POBox 14 ...

ABSTRACT Climate change may affect the phenology of some parts of food chains more strongly than others, which leads to a disruption of synchronization within food chains. We describe three different methods to assess whether the change in laying date in bird populations has been able to maintain synchronization, illustrated with our own work on great tits (Parus major). These show: (1) the date of peak abundance of caterpillars has advanced, but great tits have not started to lay earlier, hence the difference in synchronization between great tits and their prey has increased; (2) selection for early laying has become stronger; and (3) great tits have reduced the incubation period (the time between laying the last egg and first hatching) to speed up their reproduction. Clearly, the change in laying date in the studied great tit population has not been able to match the shifts in underlying levels of the food chain. We offer two hypotheses in explanation, and discuss how they can be tested by manipulating laying date under field conditions and by comparing populations on a large spatial scale. We argue that the lack of advancement of laying date may be caused by a differential change of temperature in early and late spring, rather than an increase in spring temperature per se. We also report mistiming in two other species due to correlative disruptions from weather variables, and encourage studies on other systems to find out how general this pattern is.

ABSTRACT Whether to disperse, and where to, are two of the most prominent decisions in an individual's life, with major consequences for reproductive success. We studied natal and breeding dispersal in the monogamous black-tailed godwit Limosa limosa limosa in the Netherlands, where they breed in agricultural grasslands. The majority of these grasslands recently changed from wet herb-rich meadows into well-drained grassland monocultures, on which godwits have a lower reproductive success. Here we examine habitat selection with a multistate mark–recapture analysis. Habitat transition probabilities between meadows and monocultures were estimated on the basis of 1810 marked chicks and 531 adults during seven years in a 8500 ha study area. Young and adult godwits may differ in habitat selection because: 1) adults may have gained experience from previous nest success where to settle, 2) younger individuals may find it harder to compete for the best territories. Both young and adults moved at a higher rate from the predominant monocultures to meadows than the other way around, thus actively selecting the habitat with better quality. However, dispersal distance of adults was not affected by previous nest success. The average dispersal distance from place of birth of godwits breeding for the first time was ten times larger than that of adult godwits. That godwits breeding in their second calendar year arrived and laid at similar dates and were equally able to select territories in areas with high breeding densities, suggests that young birds were not competitively inferior to adults. Although on monocultures reproduction is insufficient to maintain constant populations, birds sometimes moved from meadows to monocultures. This explains why even after 30 years of land-use intensification, godwits still breed in low-quality habitat. The adjustment to changing habitat conditions at the population level appears to be a slow process.

The environment of meadowbirds in The Neth-erlands was subject to extreme changes during the last century (Beintema et al. 1995). Detri-mental conditions – in particular the advanced mowing date – are thought to have lead to the elimination of most offspring of birds that initi-ate ...

Climate change has differentially affected the timing of seasonal events for interacting trophic levels, and this has often led to increased selection on seasonal timing. Yet, the environmental variables driving this selection have rarely been identified, limiting our ability to predict future ecological impacts of climate change. Using a dataset spanning 31 years from a natural population of pied flycatchers (Ficedula hypoleuca), we show that directional selection on timing of reproduction intensified in the first two decades (1980-2000) but weakened during the last decade (2001-2010). Against expectation, this pattern could not be explained by the temporal variation in the phenological mismatch with food abundance. We therefore explored an alternative hypothesis that selection on timing was affected by conditions individuals experience when arriving in spring at the breeding grounds: arriving early in cold conditions may reduce survival. First, we show that in female recruits, spr...

Environmental conditions under which species reproduce have major consequences on breeding success and subsequent fitness. Therefore breeding habitat choice is ultimately important. Studies rarely address the potential fitness pay-offs of alternative natural breeding habitats by experimental translocation. Here we present a new tool to study fitness consequences of free living birds in different habitats. We translocated a migratory passerine, the pied flycatcher (Ficedula hypoleuca), to a novel site, where pairs were subjected to a short stay (2-4 days) in a nest box-equipped aviary before being released. We show that it is technically possible to retain birds in the new area for breeding, allowing the study of reproductive consequences of dispersal under natural conditions. The translocation resulted in an extension of the interval between arrival and egg laying of four days, highlighting the importance of having an adequate control group. Clutch size and nestling parameters did n...