Parental care is widespread in Archosaurs (birds, crocodilians, dinosaurs and pterosaurs), and th... more Parental care is widespread in Archosaurs (birds, crocodilians, dinosaurs and pterosaurs), and this group provides a useful model for the evolution of parent-offspring interactions. While offspring signalling has been well-studied in birds, the modulation of parental care in crocodilians remains an open question. Here we show that acoustic communication has a key role in the dynamics of crocodilian' mother-offspring relationships. We found embedded information about the emitter's size in juvenile calls of several species, and experimentally demonstrated that Nile crocodile mothers breeding in the wild are less receptive to the calls of larger juveniles. Using synthetized sounds, we further showed that female' reaction depends on call pitch, an important cue bearing size information. Changes in acoustic interactions may thus go with the break of maternal care as well as dispersal of juvenile crocodilians. This process could have characterized other archosaurs displaying rapid early growth such as dinosaurs and pterosaurs. Crocodilians and birds are the modern representatives of archosaurs, a monophyletic group that also includes the extinct dinosaurs and pterosaurs 1,2. There is currently a great interest in understanding the evolution of the archausorian lineage 3 since this group has led to a diversity of species showing developed cognitive and social abilities comparable to mammals, such as social cooperation (in birds 4 , and crocodilians 5) and vocal learning (in birds 6,7). As crocodilians diverged from birds more than 240 million years ago 8 , they are of primary interest in the reconstruction of ancestral archosaurian biology 9. Together with genetic studies 10,11 , investigations on other biological traits of crocodilians will help in providing a comprehensive view of the archosaur evolution 12–14. Specifically, knowledge about crocodilian social behaviours is an important issue, which could bring relevant information about the process of their implementation during the history of archosaurs. Here we focus on parental care, a behavioural trait widely shared among archosaurs. Archosaurs are oviparous, and one or both parents of all but a few species take care of the eggs by incubating and/or guarding the nest, and the hatchlings by feeding and/or guarding them (reviewed for birds 15 ; for crocodilians 2,16,17). Moreover, there are substantial records showing that fossil archosaurs also displayed parental care 18–21 (although the case for post-hatching care in pterosaurs is rather weak 22). Thus, parental care constitutes a behavioural feature that deserves to be studied in living archosaurs with the aim of understanding the phylogenetical, physiological and ecological factors that have driven their evolution. Specifically, deciphering how interactions within the family are modulated by communication signals represents a major focal point.
The Okavango river along the panhandle of the Delta, in Botswana, is home to many wildlife specie... more The Okavango river along the panhandle of the Delta, in Botswana, is home to many wildlife species as well as to many large village communities. Local communities rely on the riverine system and its resources for subsistence and commerce. Activities associated with the utilization of these resources are governed by the fluctuating water levels of the river, which inhibit access during high water levels and allow access during low water levels. The high intensity of activities, such as reed harvesting, fishing and increased tourism, during low water periods coincides with the breeding season of many wildlife species in the system, including the Nile crocodile (Crocodylus niloticus). Over 90% of crocodile breeding areas in the Delta are found only in the panhandle region. The association between the intensity of human activities in the floodplains and crocodile nesting activity means that much of the habitat required for nesting is vulnerable to human disturbance and this could have severe negative impacts on the future of the Okavango crocodile population. The study evaluated habitat vulnerability by mapping and spatially comparing habitat suitability, based on optimum environmental requirements for crocodile nesting, and human disturbance factors. A detailed crocodile nesting survey was carried out to locate and test all nesting sites according to criteria selected by species experts. The results from the survey were used to locate suitable nesting habitat in the study area by analysis in a Geographic Information System (GIS). Disturbance factors were visually identified and their locations in the study area spatially mapped. Their spatial influences on crocodile nesting were used as factors in a Multi-Criteria Evaluation (MCE) that evaluated the combined effect of the disturbances on the area defined as suitable crocodile habitat. The results indicate the extent of habitat vulnerable to human disturbances. The results from the study show that 59% of once suitable crocodile habitat is currently disturbed by human activities. Most of the remaining 41% of undisturbed habitat is located along the Moremi/Phillipa side channel, which represents a core area for protection measures to be instated. The study recommends the declaration of a crocodile nesting sanctuary in this side channel to ensure the breeding success of this keystone species.
Mercury is a global neurotoxicant especially dangerous in wetlands and newly flooded areas which ... more Mercury is a global neurotoxicant especially dangerous in wetlands and newly flooded areas which can be sites of enhanced monomethylmercury, a form of mercury that can be readily biomagnified. The study was conducted in the Okavango Delta, Botswana, a wetland ecosystem characterized by both permanent and seasonal floodplains. Because of the biogeochemical cycling properties of mercury it is expected that wetlands can potentially be sites of elevated levels of monomethylmercury which hold potential threats for both the subsistence fishing communities as well as crocodiles. Samples from individual crocodiles Crocodylus niloticus, fish (Clarius gariepinus, Oreochromis andersoni, Serranochromis angusticeps and juvenile Tilapia sp.), macrophytes (Nymphaea sp.) and bottom channel sediments were collected from the Delta and analysed for Mercury levels. The results showed significant evidence of mercury biomagnification with mean concentrations for fish and crocodiles an order of magnitude higher than macrophytes and sediment. This exploratory study presents evidence for mercury biomagnification in the Okavango ecosystem
The Okavango Crocodile Monitoring Program (OCMP) has been running since the Okavango Crocodile Re... more The Okavango Crocodile Monitoring Program (OCMP) has been running since the Okavango Crocodile Research Group from the University of Stellenbosch ended their project in 2006.The complete database for both research projects is held by the OCMP and continually updated as new crocodiles are captured. To date the database contains over 2000 crocodiles, each of which has the corresponding GPS location and detailed morphological data. This is one of the largest databases of wild captured Nile crocodiles in the world and provides an excellent platform from which a number of current scientific studies are running, including reassessment of population status and health including recruitment and nesting patterns, long-term growth rates in the wild, isotope and urine analysis to assess heavy metal content, and assessment of farm-release successes. The OCMP has also captured crocodiles in the Okavango catchment area in Angola and has discovered what appears to be a fairly healthy recruitment upstream from the Okavango River. While current capture efforts are not as intensive as they were in the past, the strategy of targeting specific size classes will certainly improve our understanding of growth rates and movements of sub-adult and adult crocodiles. This presentation will summarize the research findings to date, discuss present work being conducted and touch on future expectations, including addressing issues of Human/crocodile conflict.
The Nile crocodile (Crocodylus niloticus) population of the Okavango Delta has undergone three ma... more The Nile crocodile (Crocodylus niloticus) population of the Okavango Delta has undergone three major periods of human-induced decline in the past century. Combined, these periods have lead to an estimated 50% reduction in the breeding population of the Okavango Nile crocodile. Although the possibility of population recruitment from two neighboring countries, namely Angola and Namibia, may exist, both countries are currently experiencing a period of major agricultural and economic development. This situation is likely to lead to an increase in crocodile- human conflict and further reduce the likelihood of recruitment into the Okavango Delta from further upstream. Therefore, knowledge concerning the breeding ecology of the Okavango Nile crocodile population and the impact of human disturbance is of critical importance for the long-term survival of this population.  This paper presents data collected over three consecutive nesting seasons in the “panhandle” region of the Okavango Delta, the primary breeding area for this population of crocodiles. Data was collected on nest location, hatching success and other physical nest site parameters. Results indicate that 50-80% of previous nesting sites are no longer in use. Additionally, nest sites are being selected on the basis of minimal human disturbance, rather than on optimal nesting parameters. Through the use of GIS techniques we propose a nesting sanctuary for Nile crocodiles in the Okavango Delta, highlighting the importance of such an area for the long-term survival of the population.
Mercury is a global neurotoxicant especially dangerous in wetlands and newly flooded areas which ... more Mercury is a global neurotoxicant especially dangerous in wetlands and newly flooded areas which can be sites of enhanced monomethylmercury, a form of mercury that can be readily biomagnified. The study was conducted in the Okavango Delta, Botswana, a wetland ecosystem characterized by both permanent and seasonal floodplains. Because of the biogeochemical cycling properties of mercury it is expected that wetlands can potentially be sites of elevated levels of monomethylmercury which hold potential threats for both the subsistence fishing communities as well as crocodiles.
Samples from individual crocodiles (Crocodylus niloticus), fish (Clarius gariepinus, Oreochromis andersoni, Serranochromis angusticeps and juvenile Tilapia sp.), macrophytes (Nymphaea sp.) and bottom channel sediments were collected from the Delta and analysed for Mercury levels.
The results showed significant evidence of mercury biomagnification with mean concentrations for fish and crocodiles an order of magnitude higher than macrophytes and sediment. This exploratory study presents evidence for mercury biomagnification in the Okavango ecosystem
Parental care is widespread in Archosaurs (birds, crocodilians, dinosaurs and pterosaurs), and th... more Parental care is widespread in Archosaurs (birds, crocodilians, dinosaurs and pterosaurs), and this group provides a useful model for the evolution of parent-offspring interactions. While offspring signalling has been well-studied in birds, the modulation of parental care in crocodilians remains an open question. Here we show that acoustic communication has a key role in the dynamics of crocodilian' mother-offspring relationships. We found embedded information about the emitter's size in juvenile calls of several species, and experimentally demonstrated that Nile crocodile mothers breeding in the wild are less receptive to the calls of larger juveniles. Using synthetized sounds, we further showed that female' reaction depends on call pitch, an important cue bearing size information. Changes in acoustic interactions may thus go with the break of maternal care as well as dispersal of juvenile crocodilians. This process could have characterized other archosaurs displaying rapid early growth such as dinosaurs and pterosaurs. Crocodilians and birds are the modern representatives of archosaurs, a monophyletic group that also includes the extinct dinosaurs and pterosaurs 1,2. There is currently a great interest in understanding the evolution of the archausorian lineage 3 since this group has led to a diversity of species showing developed cognitive and social abilities comparable to mammals, such as social cooperation (in birds 4 , and crocodilians 5) and vocal learning (in birds 6,7). As crocodilians diverged from birds more than 240 million years ago 8 , they are of primary interest in the reconstruction of ancestral archosaurian biology 9. Together with genetic studies 10,11 , investigations on other biological traits of crocodilians will help in providing a comprehensive view of the archosaur evolution 12–14. Specifically, knowledge about crocodilian social behaviours is an important issue, which could bring relevant information about the process of their implementation during the history of archosaurs. Here we focus on parental care, a behavioural trait widely shared among archosaurs. Archosaurs are oviparous, and one or both parents of all but a few species take care of the eggs by incubating and/or guarding the nest, and the hatchlings by feeding and/or guarding them (reviewed for birds 15 ; for crocodilians 2,16,17). Moreover, there are substantial records showing that fossil archosaurs also displayed parental care 18–21 (although the case for post-hatching care in pterosaurs is rather weak 22). Thus, parental care constitutes a behavioural feature that deserves to be studied in living archosaurs with the aim of understanding the phylogenetical, physiological and ecological factors that have driven their evolution. Specifically, deciphering how interactions within the family are modulated by communication signals represents a major focal point.
The Okavango river along the panhandle of the Delta, in Botswana, is home to many wildlife specie... more The Okavango river along the panhandle of the Delta, in Botswana, is home to many wildlife species as well as to many large village communities. Local communities rely on the riverine system and its resources for subsistence and commerce. Activities associated with the utilization of these resources are governed by the fluctuating water levels of the river, which inhibit access during high water levels and allow access during low water levels. The high intensity of activities, such as reed harvesting, fishing and increased tourism, during low water periods coincides with the breeding season of many wildlife species in the system, including the Nile crocodile (Crocodylus niloticus). Over 90% of crocodile breeding areas in the Delta are found only in the panhandle region. The association between the intensity of human activities in the floodplains and crocodile nesting activity means that much of the habitat required for nesting is vulnerable to human disturbance and this could have severe negative impacts on the future of the Okavango crocodile population. The study evaluated habitat vulnerability by mapping and spatially comparing habitat suitability, based on optimum environmental requirements for crocodile nesting, and human disturbance factors. A detailed crocodile nesting survey was carried out to locate and test all nesting sites according to criteria selected by species experts. The results from the survey were used to locate suitable nesting habitat in the study area by analysis in a Geographic Information System (GIS). Disturbance factors were visually identified and their locations in the study area spatially mapped. Their spatial influences on crocodile nesting were used as factors in a Multi-Criteria Evaluation (MCE) that evaluated the combined effect of the disturbances on the area defined as suitable crocodile habitat. The results indicate the extent of habitat vulnerable to human disturbances. The results from the study show that 59% of once suitable crocodile habitat is currently disturbed by human activities. Most of the remaining 41% of undisturbed habitat is located along the Moremi/Phillipa side channel, which represents a core area for protection measures to be instated. The study recommends the declaration of a crocodile nesting sanctuary in this side channel to ensure the breeding success of this keystone species.
Mercury is a global neurotoxicant especially dangerous in wetlands and newly flooded areas which ... more Mercury is a global neurotoxicant especially dangerous in wetlands and newly flooded areas which can be sites of enhanced monomethylmercury, a form of mercury that can be readily biomagnified. The study was conducted in the Okavango Delta, Botswana, a wetland ecosystem characterized by both permanent and seasonal floodplains. Because of the biogeochemical cycling properties of mercury it is expected that wetlands can potentially be sites of elevated levels of monomethylmercury which hold potential threats for both the subsistence fishing communities as well as crocodiles. Samples from individual crocodiles Crocodylus niloticus, fish (Clarius gariepinus, Oreochromis andersoni, Serranochromis angusticeps and juvenile Tilapia sp.), macrophytes (Nymphaea sp.) and bottom channel sediments were collected from the Delta and analysed for Mercury levels. The results showed significant evidence of mercury biomagnification with mean concentrations for fish and crocodiles an order of magnitude higher than macrophytes and sediment. This exploratory study presents evidence for mercury biomagnification in the Okavango ecosystem
The Okavango Crocodile Monitoring Program (OCMP) has been running since the Okavango Crocodile Re... more The Okavango Crocodile Monitoring Program (OCMP) has been running since the Okavango Crocodile Research Group from the University of Stellenbosch ended their project in 2006.The complete database for both research projects is held by the OCMP and continually updated as new crocodiles are captured. To date the database contains over 2000 crocodiles, each of which has the corresponding GPS location and detailed morphological data. This is one of the largest databases of wild captured Nile crocodiles in the world and provides an excellent platform from which a number of current scientific studies are running, including reassessment of population status and health including recruitment and nesting patterns, long-term growth rates in the wild, isotope and urine analysis to assess heavy metal content, and assessment of farm-release successes. The OCMP has also captured crocodiles in the Okavango catchment area in Angola and has discovered what appears to be a fairly healthy recruitment upstream from the Okavango River. While current capture efforts are not as intensive as they were in the past, the strategy of targeting specific size classes will certainly improve our understanding of growth rates and movements of sub-adult and adult crocodiles. This presentation will summarize the research findings to date, discuss present work being conducted and touch on future expectations, including addressing issues of Human/crocodile conflict.
The Nile crocodile (Crocodylus niloticus) population of the Okavango Delta has undergone three ma... more The Nile crocodile (Crocodylus niloticus) population of the Okavango Delta has undergone three major periods of human-induced decline in the past century. Combined, these periods have lead to an estimated 50% reduction in the breeding population of the Okavango Nile crocodile. Although the possibility of population recruitment from two neighboring countries, namely Angola and Namibia, may exist, both countries are currently experiencing a period of major agricultural and economic development. This situation is likely to lead to an increase in crocodile- human conflict and further reduce the likelihood of recruitment into the Okavango Delta from further upstream. Therefore, knowledge concerning the breeding ecology of the Okavango Nile crocodile population and the impact of human disturbance is of critical importance for the long-term survival of this population.  This paper presents data collected over three consecutive nesting seasons in the “panhandle” region of the Okavango Delta, the primary breeding area for this population of crocodiles. Data was collected on nest location, hatching success and other physical nest site parameters. Results indicate that 50-80% of previous nesting sites are no longer in use. Additionally, nest sites are being selected on the basis of minimal human disturbance, rather than on optimal nesting parameters. Through the use of GIS techniques we propose a nesting sanctuary for Nile crocodiles in the Okavango Delta, highlighting the importance of such an area for the long-term survival of the population.
Mercury is a global neurotoxicant especially dangerous in wetlands and newly flooded areas which ... more Mercury is a global neurotoxicant especially dangerous in wetlands and newly flooded areas which can be sites of enhanced monomethylmercury, a form of mercury that can be readily biomagnified. The study was conducted in the Okavango Delta, Botswana, a wetland ecosystem characterized by both permanent and seasonal floodplains. Because of the biogeochemical cycling properties of mercury it is expected that wetlands can potentially be sites of elevated levels of monomethylmercury which hold potential threats for both the subsistence fishing communities as well as crocodiles.
Samples from individual crocodiles (Crocodylus niloticus), fish (Clarius gariepinus, Oreochromis andersoni, Serranochromis angusticeps and juvenile Tilapia sp.), macrophytes (Nymphaea sp.) and bottom channel sediments were collected from the Delta and analysed for Mercury levels.
The results showed significant evidence of mercury biomagnification with mean concentrations for fish and crocodiles an order of magnitude higher than macrophytes and sediment. This exploratory study presents evidence for mercury biomagnification in the Okavango ecosystem
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Papers by Vince Shacks
The study evaluated habitat vulnerability by mapping and spatially comparing habitat suitability, based on optimum environmental requirements for crocodile nesting, and human disturbance factors. A detailed crocodile nesting survey was carried out to locate and test all nesting sites according to criteria selected by species experts. The results from the survey were used to locate suitable nesting habitat in the study area by analysis in a Geographic Information System (GIS). Disturbance factors were visually identified and their locations in the study area spatially mapped. Their spatial influences on crocodile nesting were used as factors in a Multi-Criteria Evaluation (MCE) that evaluated the combined effect of the disturbances on the area defined as suitable crocodile habitat. The results indicate the extent of habitat vulnerable to human disturbances.
The results from the study show that 59% of once suitable crocodile habitat is currently disturbed by human activities. Most of the remaining 41% of undisturbed habitat is located along the Moremi/Phillipa side channel, which represents a core area for protection measures to be instated. The study recommends the declaration of a crocodile nesting sanctuary in this side channel to ensure the breeding success of this keystone species.
Conference Presentations by Vince Shacks

This paper presents data collected over three consecutive nesting seasons in the “panhandle” region of the Okavango Delta, the primary breeding area for this population of crocodiles. Data was collected on nest location, hatching success and other physical nest site parameters. Results indicate that 50-80% of previous nesting sites are no longer in use. Additionally, nest sites are being selected on the basis of minimal human disturbance, rather than on optimal nesting parameters. Through the use of GIS techniques we propose a nesting sanctuary for Nile crocodiles in the Okavango Delta, highlighting the importance of such an area for the long-term survival of the population.
Samples from individual crocodiles (Crocodylus niloticus), fish (Clarius gariepinus, Oreochromis andersoni, Serranochromis angusticeps and juvenile Tilapia sp.), macrophytes (Nymphaea sp.) and bottom channel sediments were collected from the Delta and analysed for Mercury levels.
The results showed significant evidence of mercury biomagnification with mean concentrations for fish and crocodiles an order of magnitude higher than macrophytes and sediment. This exploratory study presents evidence for mercury biomagnification in the Okavango ecosystem
The study evaluated habitat vulnerability by mapping and spatially comparing habitat suitability, based on optimum environmental requirements for crocodile nesting, and human disturbance factors. A detailed crocodile nesting survey was carried out to locate and test all nesting sites according to criteria selected by species experts. The results from the survey were used to locate suitable nesting habitat in the study area by analysis in a Geographic Information System (GIS). Disturbance factors were visually identified and their locations in the study area spatially mapped. Their spatial influences on crocodile nesting were used as factors in a Multi-Criteria Evaluation (MCE) that evaluated the combined effect of the disturbances on the area defined as suitable crocodile habitat. The results indicate the extent of habitat vulnerable to human disturbances.
The results from the study show that 59% of once suitable crocodile habitat is currently disturbed by human activities. Most of the remaining 41% of undisturbed habitat is located along the Moremi/Phillipa side channel, which represents a core area for protection measures to be instated. The study recommends the declaration of a crocodile nesting sanctuary in this side channel to ensure the breeding success of this keystone species.

This paper presents data collected over three consecutive nesting seasons in the “panhandle” region of the Okavango Delta, the primary breeding area for this population of crocodiles. Data was collected on nest location, hatching success and other physical nest site parameters. Results indicate that 50-80% of previous nesting sites are no longer in use. Additionally, nest sites are being selected on the basis of minimal human disturbance, rather than on optimal nesting parameters. Through the use of GIS techniques we propose a nesting sanctuary for Nile crocodiles in the Okavango Delta, highlighting the importance of such an area for the long-term survival of the population.
Samples from individual crocodiles (Crocodylus niloticus), fish (Clarius gariepinus, Oreochromis andersoni, Serranochromis angusticeps and juvenile Tilapia sp.), macrophytes (Nymphaea sp.) and bottom channel sediments were collected from the Delta and analysed for Mercury levels.
The results showed significant evidence of mercury biomagnification with mean concentrations for fish and crocodiles an order of magnitude higher than macrophytes and sediment. This exploratory study presents evidence for mercury biomagnification in the Okavango ecosystem