Ewa Krzyszczyk | Georgetown University (original) (raw)

Papers by Ewa Krzyszczyk

Dataset used for modeling the effects of birth order on weaning ag

Reproductive senescence is evident across many mammalian species. An emerging perspective conside... more Reproductive senescence is evident across many mammalian species. An emerging perspective considers components of reproductive senescence as evolutionarily distinct phenomena: fertility senescence and maternal-effect senescence. While fertility senescence is regarded as the aging of reproductive physiology, maternal-effect senescence pertains to the declining capacity to provision and rear surviving offspring due to age. Both contribute to reproductive failure in utero making it difficult to differentiate between the two prenatally in the wild. We investigated both components in a long-lived mammal with prolonged maternal care through three parameters: calf survival, interbirth interval (IBI), and lactation period. We provide clear evidence for reproductive senescence in a wild population of bottlenose dolphins (Tursiops aduncus) using 34+ years of longitudinal data on 229 adult females and 562 calves. Calf survival decreased with maternal age, and calves with older mothers had lower survival than predicted by birth order, suggesting maternal-effect senescence. Both lactation period and IBIs increased with maternal age, and IBIs increased regardless of calf mortality, indicating interactions between fertility and maternal-effect senescence. Of calves that survived to weaning, last-born calves weaned later than earlier-born calves, evidence of terminal investment, a mitigating strategy given reduced reproductive value caused by either components of reproductive senescence

Sexual segregation is widespread in mammals, although the proximate causes are poorly understood ... more Sexual segregation is widespread in mammals, although the proximate causes are poorly understood in monomorphic species. Indo-Pacific bottlenose dolphins (Tursiops aduncus), which exhibit a high degree of fission-fusion dynamics, offer a useful lens to examine the ecological and social drivers of sexual segregation. While ecological hypotheses suggest that sexual segregation is a by-product of sex-specific ecological preferences (e.g. related to habitat, foraging, or predator avoidance), the social hypothesis proffers that segregation results from same-sex preferences (e.g. due to cooperative benefits) and/or opposite-sex avoidance (e.g. due to competitive or exploitative interactions). Indo-Pacific bottlenose dolphin females range from nearly solitary to highly sociable. Males associate in alliances that cooperate to sequester individual females and exclude competing males. Given evidence for allied sexual coercion, our primary hypothesis was that sexual segregation is driven by female avoidance of aggressive males. However, given robust evidence for sex-biased foraging tactics, ecological factors likely also contribute. Using the Sexual Segregation and Aggregation Statistic with 17,468 sighting records spanning 31 years, we found strong sexual segregation. Unique to our work, we analyzed the direction of joins and leaves between males and females from focal observations (N=10,715 fission-fusion events, 87 females, 111 males) to determine which sex drives sexual segregation. Females drove segregation by rarely joining and often leaving males. Although ecological factors likely reinforce sexual segregation, social factors predominate. This study demonstrates a sex-bias in fission-fusion dynamics in a socially complex wild mammal population and offers strong empirical support to the social hypothesis of sexual segregation

Although of theoretical interest, the juvenile period in mammals is a relatively neglected area o... more Although of theoretical interest, the juvenile period in mammals is a relatively neglected area of research. In large-brained and social mammals, such as bottlenose dolphins, where juvenile periods are prolonged, life history theorists assume they must need or use this period to solve specific adaptive problems, such as growth, skill development or social bond formation. Here, I examine the period of immaturity in bottlenose dolphins with a diverse set of approaches: physiological and hormonal development, age-and sex-specific survival, and juvenile behavior and relationships. The 30-year Shark Bay dataset provides a unique opportunity to investigate these features longitudinally. Chapter 1 investigates the ontogeny and possible functions of ventral speckling in bottlenose dolphins in Shark Bay. Speckles first appear at 10 yrs of age around the genital area, just prior to the typical age of first pregnancy. Throughout a dolphins' lifespan, speckles increase in number and density. The most promising functional explanation is that speckles offer cues to reproductive maturity, social status (age) or condition. Chapter 2 investigates age and sex-specific survival rates. 1 st yr calves had significantly lower survival rates than older calves or juveniles. Adult survival was I would like to thank my thesis committee. Dr. Kathryn Sandberg, Dr. Peter Armbruster, and Dr. Lisa Singh were incredibly helpful, enthusiastic and supporting throughout my entire PhD and my work would not have been possible without them. I would like to especially thank Dr. Armbruster for being on all my committees throughout my time at Georgetown, for always being available and pushing me to be my best by always asking the toughest questions. I owe a particular debt of gratitude to Dr. Sandberg who took a huge leap of faith by opening up her lab to test my crazy ideas. Last but not least Dr. Singh, without whom our long-term database would not be in the shape it is today without her unrelenting dedication. I realize that I am extremely privileged to have had access to over 28 years of highly detailed data, actually working with it was not an easy undertaking. Thankfully, I was fortunate enough to have had the assistance of several knowledgeable people:

Marine Mammal Science, 2012

A report on six cases of seagrass-associated gastric impaction in bottlenose dolphins (Tursiops sp.

Frontiers in Marine Science

As demands for wildlife tourism increase, provisioning has become a popular means of providing up... more As demands for wildlife tourism increase, provisioning has become a popular means of providing up-close viewing to the public. At Monkey Mia, Shark Bay, Australia, up to five adult female Indo-Pacific bottlenose dolphins (Tursiops aduncus) visit a 100 m stretch of beach daily to receive fish handouts. In 2011, a severe marine heatwave (MHW) devastated seagrass and fish populations in Shark Bay. Offspring survival declined precipitously among seagrass specialists (dolphins that forage disproportionately in seagrass habitat). As all provisioned dolphins at the site are seagrass specialists, we examined how provisioned and non-provisioned seagrass specialists responded to the MHW. Using 27 years of data we compare habitat use, home range size, calf mortality, and predation risk between provisioned and non-provisioned females and their offspring before and after the MHW. Our results show that provisioned females have extremely small home ranges compared to non-provisioned females, a pat...

Behavioral Ecology

The juvenile period is a challenging life-history stage, especially in species with a high degree... more The juvenile period is a challenging life-history stage, especially in species with a high degree of fission–fusion dynamics, such as bottlenose dolphins, where maternal protection is virtually absent. Here, we examined how juvenile male and female bottlenose dolphins navigate this vulnerable period. Specifically, we examined their grouping patterns, activity budget, network dynamics, and social associations in the absence of adults. We found that juveniles live in highly dynamic groups, with group composition changing every 10 min on average. Groups were generally segregated by sex, and segregation was driven by same-sex preference rather than opposite-sex avoidance. Juveniles formed strong associations with select individuals, especially kin and same-sex partners, and both sexes formed cliques with their preferred partners. Sex-specific strategies in the juvenile period reflected adult reproductive strategies, in which the exploration of potential social partners may be more impor...

Proceedings of the Royal Society B, 2018

Reproductive senescence is evident across many mammalian species. An emerging perspective conside... more Reproductive senescence is evident across many mammalian species. An emerging perspective considers components of reproductive senescence as evolutionarily distinct phenomena: fertility senescence and maternal-effect senescence. While fertility senescence is regarded as the ageing of reproductive physiology, maternal-effect senescence pertains to the declining capacity to provision and rear surviving offspring due to age. Both contribute to reproductive failure in utero making it difficult to differentiate between the two prenatally in the wild. We investigated both components in a long-lived mammal with prolonged maternal care through three parameters: calf survival , interbirth interval (IBI) and lactation period. We provide clear evidence for reproductive senescence in a wild population of bottlenose dolphins (Tur-siops aduncus) using 34þ years of longitudinal data on 229 adult females and 562 calves. Calf survival decreased with maternal age, and calves with older mothers had lower survival than predicted by birth order, suggesting maternal-effect senescence. Both lactation period and IBIs increased with maternal age, and IBIs increased regardless of calf mortality, indicating interactions between fertility and maternal-effect senescence. Of calves that survived to weaning, last-born calves weaned later than earlier-born calves, evidence of terminal investment, a mitigating strategy given reduced reproductive value caused by either components of reproductive senescence.

Long-term studies often rely on natural markings for individual identification across time. The p... more Long-term studies often rely on natural markings for individual identification across time. The primary method for identification in small cetaceans relies on dorsal fin shape, scars and other natural markings. However, dorsal fin markings can vary substantially over time and the dorsal fin can become unrecognizable after an encounter with a boat or shark. Although dorsal fins have the advantage in that they always break the water surface when the cetacean breathes, other physical features, such as body scars and pigmentation patterns can supplement. The goal of this study was to explore the use of dorso-lateral pigment patterns to identify wild bottlenose dolphins. We employed photographic pigment matching tests to determine if pigmentation patterns showed (1) longitudinal consistency and (2) bilateral symmetry using a 30-year photographic database of bottlenose dolphin (Tursiops aduncus). We compared experienced dolphin researchers and inexperienced undergraduate student subjects in their ability to accurately match images. Both experienced and inexperienced subjects correctly matched dolphin individuals at a rate significantly above chance, even though they only had ten seconds to make the match. These results demonstrate that pigment patterns can be used to reliably identify individual wild bottlenose dolphins, and likely other small cetacean species at other sites.

Sex differences in adult behaviour are well documented, but less is known about the ontogeny of t... more Sex differences in adult behaviour are well documented, but less is known about the ontogeny of these differences. In mammals, the transition to independence, from infancy to the juvenile period, is when these sex differences are likely to become prominent. Here, we examined sex differences in behavioural development among calf and juvenile bottlenose dolphins (Tursiops aduncus) from two years pre-weaning to two years post-weaning and whether these differences were consistent, or not, with three non-mutually exclusive hypotheses regarding the function of the juvenile period: the social skills, protection/safety, and energy allocation hypothesis. All hypotheses received some support, but strikingly so for females. First, sex differences in the nature and quality of juvenile social bonds appear to foreshadow adult association patterns. Juveniles had a greater proportion of same-sex associates than calves. Second, although neither sex increased their number of associates from infancy to juvenility, a pattern that might mitigate predation risk, avoidance between juveniles and adult males suggests that both sexes reduce the likelihood of conspecific aggression. This pattern was more marked for juvenile females. Third, females, but not males, increased foraging rates from late infancy to the early juvenile period, even surpassing typical adult female foraging rates. This is likely related to the future energetic demands of maternal investment and skill development required for specialized foraging tactics, which are female biased in this population. This study provides a first step towards understanding the transition into independence for cetaceans, insight into how sex differences develop and a glimpse into the function of the juvenile period.

Network null models are important to drawing conclusions about individual- and population-(or gra... more Network null models are important to drawing conclusions about individual- and population-(or graph) level metrics. While the null models of binary networks are well studied, recent literature on weighted networks suggests that: (1) many so-called ‘weighted metrics’ do not actually depend on weights, and (2) many metrics that supposedly measure higher-order social structure actually are highly correlated with individual-level attributes. This is important for behavioural ecology studies where weighted network analyses predominate, but there is no consensus on how null models should be specified. Using real social networks, we developed three null models that address two technical challenges in the networks of social animals: (1) how to specify null models that are suitable for ‘proportion-weighted networks’ based on indices such as the half-weight index; and (2) how to condition on the degree- and strength-sequence and both. We compared 11 metrics with each other and against null-model expectations for 10 social networks of bottlenose dolphin, Tursiops aduncus, from Shark Bay, Australia. Observed metric values were similar to null-model expectations for some weighted metrics, such as centrality measures, disparity and connectivity, whereas other metrics such as affinity and clustering were informative about dolphin social structure. Because weighted metrics can differ in their sensitivity to the degree-sequence or strength-sequence, conditioning on both is a more reliable and conservative null model than the more common strength-preserving null-model for weighted networks. Other social structure analyses, such as community partitioning by weighted Modularity optimization, were much less sensitive to the underlying null-model. Lastly, in contrast to results in other scientific disciplines, we found that many weighted metrics do not depend trivially on topology; rather, the weight distribution contains important information about dolphin social structure.

Effective foraging is necessary for nearly all animals, but most animals are not born with adult-... more Effective foraging is necessary for nearly all animals, but most animals are not born with adult-like foraging performance. Instead, foraging skills are developed during an individual’s lifetime. Life-history theory predicts that adult-level foraging performance should be reached prior to the start of reproduction, but for most species, we know little about age-specific foraging in the wild. Here, we examine lifetime changes in foraging performance for a group of female wild bottlenose dolphins that use marine sponge tools to forage. After controlling for ecological effects and developmental changes in activity budgets, we show that females continue to improve in 3 aspects of foraging until a peak at around midlife, well after dolphins reach physical and sexual maturity. The factors that lead to this improved performance are unknown, but likely include learning and increasing physical ability. Dolphins’ peak in foraging performance also coincided with a peak in reproduction, with middle-aged females maximizing foraging efficiency and having the highest probability of lactating. Thus, inadequate mastery of foraging behaviors, such as tool use in bottlenose dolphins, does not limit the onset of reproduction, but improvement in foraging skill may help maximize age-specific reproduction and lifetime fitness.

Activity budget data are essential for determining behavioral responses to physiological and ecol... more Activity budget data are essential for determining behavioral responses to physiological and ecological variables. Yet, few studies are available to investigate the robustness, accuracy, and biases of the methods used to estimate activity budgets for cetaceans. In this study, we compare activity budgets of 55 adult female bottlenose dolphins in Shark Bay, Australia derived from two methods: surveys (n = 6,903) and focal follows (n = 1,185, totaling 2,721 h of observation). Activity budgets estimated from survey data differed in all behavioral states compared to focal follow data. However, when controlling for temporal autocorrelation, only time spent socializing and time spent traveling remained disparate between the methods. To control for biases associated with assigning group-level behavior to individuals, we also compared survey and focal follow activity budgets for lone females. Here we found differences between methods in time spent foraging and traveling regardless of whether we controlled for temporal autocorrelation, which suggests detection biases likely play a role in explaining differences in activity budget estimates between the two methodologies. Our results suggest that surveys are less representative of individual-level activity budgets, and thus, when individual-level knowledge about behavior is needed, focal follows are preferred.

Marine Mammal Science, 2013

PloS one, 2010

Background: Molecular tools are now widely used to address crucial management and conservation qu... more Background: Molecular tools are now widely used to address crucial management and conservation questions. To date, dart biopsying has been the most commonly used method for collecting genetic data from cetaceans; however, this method has some drawbacks. Dart biopsying is considered inappropriate for young animals and has recently come under scrutiny from ethical boards, conservationists, and the general public. Thus, identifying alternative genetic collection techniques for cetaceans remains a priority, especially for internationally protected species.

Marine Mammal Science, 2011

To date, color patterns have been used to assess cetacean age and taxonomic status, but few studi... more To date, color patterns have been used to assess cetacean age and taxonomic status, but few studies have determined precise correlates of coloration with known age or investigated its function. Here, we examine the ontogeny of speckling in 88 bottlenose dolphins (Tursiops sp.) in Shark Bay, Australia, of known age, tracked from birth to age 34. Ventral speckles first appear in the genital area at a mean age of 10.2 ± 0.35 yr (range = 7.6-12.7 yr). Throughout their life span, speckles increase in number and density, particularly along the ventral and lateral sides. The timing of speckle onset does not significantly differ by sex but is related to sexual maturity in females. The age of speckle onset in the genital area correlates with the age of first known parturition. In terms of speckle function, we discuss two hypotheses commonly proffered to explain color variation, concealment, and communication. Concealment from predators or prey is unlikely to explain speckle development in Shark Bay Tursiops because the onset occurs long after peak predation risk and initial hunting success (at 3 mo of age). We suggest that speckle patterns offer reliable cues on reproductive status and/or condition and could, thus, serve a communicative or some other function.

Dataset used for modeling the effects of birth order on weaning ag

Reproductive senescence is evident across many mammalian species. An emerging perspective conside... more Reproductive senescence is evident across many mammalian species. An emerging perspective considers components of reproductive senescence as evolutionarily distinct phenomena: fertility senescence and maternal-effect senescence. While fertility senescence is regarded as the aging of reproductive physiology, maternal-effect senescence pertains to the declining capacity to provision and rear surviving offspring due to age. Both contribute to reproductive failure in utero making it difficult to differentiate between the two prenatally in the wild. We investigated both components in a long-lived mammal with prolonged maternal care through three parameters: calf survival, interbirth interval (IBI), and lactation period. We provide clear evidence for reproductive senescence in a wild population of bottlenose dolphins (Tursiops aduncus) using 34+ years of longitudinal data on 229 adult females and 562 calves. Calf survival decreased with maternal age, and calves with older mothers had lower survival than predicted by birth order, suggesting maternal-effect senescence. Both lactation period and IBIs increased with maternal age, and IBIs increased regardless of calf mortality, indicating interactions between fertility and maternal-effect senescence. Of calves that survived to weaning, last-born calves weaned later than earlier-born calves, evidence of terminal investment, a mitigating strategy given reduced reproductive value caused by either components of reproductive senescence

Sexual segregation is widespread in mammals, although the proximate causes are poorly understood ... more Sexual segregation is widespread in mammals, although the proximate causes are poorly understood in monomorphic species. Indo-Pacific bottlenose dolphins (Tursiops aduncus), which exhibit a high degree of fission-fusion dynamics, offer a useful lens to examine the ecological and social drivers of sexual segregation. While ecological hypotheses suggest that sexual segregation is a by-product of sex-specific ecological preferences (e.g. related to habitat, foraging, or predator avoidance), the social hypothesis proffers that segregation results from same-sex preferences (e.g. due to cooperative benefits) and/or opposite-sex avoidance (e.g. due to competitive or exploitative interactions). Indo-Pacific bottlenose dolphin females range from nearly solitary to highly sociable. Males associate in alliances that cooperate to sequester individual females and exclude competing males. Given evidence for allied sexual coercion, our primary hypothesis was that sexual segregation is driven by female avoidance of aggressive males. However, given robust evidence for sex-biased foraging tactics, ecological factors likely also contribute. Using the Sexual Segregation and Aggregation Statistic with 17,468 sighting records spanning 31 years, we found strong sexual segregation. Unique to our work, we analyzed the direction of joins and leaves between males and females from focal observations (N=10,715 fission-fusion events, 87 females, 111 males) to determine which sex drives sexual segregation. Females drove segregation by rarely joining and often leaving males. Although ecological factors likely reinforce sexual segregation, social factors predominate. This study demonstrates a sex-bias in fission-fusion dynamics in a socially complex wild mammal population and offers strong empirical support to the social hypothesis of sexual segregation

Although of theoretical interest, the juvenile period in mammals is a relatively neglected area o... more Although of theoretical interest, the juvenile period in mammals is a relatively neglected area of research. In large-brained and social mammals, such as bottlenose dolphins, where juvenile periods are prolonged, life history theorists assume they must need or use this period to solve specific adaptive problems, such as growth, skill development or social bond formation. Here, I examine the period of immaturity in bottlenose dolphins with a diverse set of approaches: physiological and hormonal development, age-and sex-specific survival, and juvenile behavior and relationships. The 30-year Shark Bay dataset provides a unique opportunity to investigate these features longitudinally. Chapter 1 investigates the ontogeny and possible functions of ventral speckling in bottlenose dolphins in Shark Bay. Speckles first appear at 10 yrs of age around the genital area, just prior to the typical age of first pregnancy. Throughout a dolphins' lifespan, speckles increase in number and density. The most promising functional explanation is that speckles offer cues to reproductive maturity, social status (age) or condition. Chapter 2 investigates age and sex-specific survival rates. 1 st yr calves had significantly lower survival rates than older calves or juveniles. Adult survival was I would like to thank my thesis committee. Dr. Kathryn Sandberg, Dr. Peter Armbruster, and Dr. Lisa Singh were incredibly helpful, enthusiastic and supporting throughout my entire PhD and my work would not have been possible without them. I would like to especially thank Dr. Armbruster for being on all my committees throughout my time at Georgetown, for always being available and pushing me to be my best by always asking the toughest questions. I owe a particular debt of gratitude to Dr. Sandberg who took a huge leap of faith by opening up her lab to test my crazy ideas. Last but not least Dr. Singh, without whom our long-term database would not be in the shape it is today without her unrelenting dedication. I realize that I am extremely privileged to have had access to over 28 years of highly detailed data, actually working with it was not an easy undertaking. Thankfully, I was fortunate enough to have had the assistance of several knowledgeable people:

Marine Mammal Science, 2012

A report on six cases of seagrass-associated gastric impaction in bottlenose dolphins (Tursiops sp.

Frontiers in Marine Science

As demands for wildlife tourism increase, provisioning has become a popular means of providing up... more As demands for wildlife tourism increase, provisioning has become a popular means of providing up-close viewing to the public. At Monkey Mia, Shark Bay, Australia, up to five adult female Indo-Pacific bottlenose dolphins (Tursiops aduncus) visit a 100 m stretch of beach daily to receive fish handouts. In 2011, a severe marine heatwave (MHW) devastated seagrass and fish populations in Shark Bay. Offspring survival declined precipitously among seagrass specialists (dolphins that forage disproportionately in seagrass habitat). As all provisioned dolphins at the site are seagrass specialists, we examined how provisioned and non-provisioned seagrass specialists responded to the MHW. Using 27 years of data we compare habitat use, home range size, calf mortality, and predation risk between provisioned and non-provisioned females and their offspring before and after the MHW. Our results show that provisioned females have extremely small home ranges compared to non-provisioned females, a pat...

Behavioral Ecology

The juvenile period is a challenging life-history stage, especially in species with a high degree... more The juvenile period is a challenging life-history stage, especially in species with a high degree of fission–fusion dynamics, such as bottlenose dolphins, where maternal protection is virtually absent. Here, we examined how juvenile male and female bottlenose dolphins navigate this vulnerable period. Specifically, we examined their grouping patterns, activity budget, network dynamics, and social associations in the absence of adults. We found that juveniles live in highly dynamic groups, with group composition changing every 10 min on average. Groups were generally segregated by sex, and segregation was driven by same-sex preference rather than opposite-sex avoidance. Juveniles formed strong associations with select individuals, especially kin and same-sex partners, and both sexes formed cliques with their preferred partners. Sex-specific strategies in the juvenile period reflected adult reproductive strategies, in which the exploration of potential social partners may be more impor...

Proceedings of the Royal Society B, 2018

Reproductive senescence is evident across many mammalian species. An emerging perspective conside... more Reproductive senescence is evident across many mammalian species. An emerging perspective considers components of reproductive senescence as evolutionarily distinct phenomena: fertility senescence and maternal-effect senescence. While fertility senescence is regarded as the ageing of reproductive physiology, maternal-effect senescence pertains to the declining capacity to provision and rear surviving offspring due to age. Both contribute to reproductive failure in utero making it difficult to differentiate between the two prenatally in the wild. We investigated both components in a long-lived mammal with prolonged maternal care through three parameters: calf survival , interbirth interval (IBI) and lactation period. We provide clear evidence for reproductive senescence in a wild population of bottlenose dolphins (Tur-siops aduncus) using 34þ years of longitudinal data on 229 adult females and 562 calves. Calf survival decreased with maternal age, and calves with older mothers had lower survival than predicted by birth order, suggesting maternal-effect senescence. Both lactation period and IBIs increased with maternal age, and IBIs increased regardless of calf mortality, indicating interactions between fertility and maternal-effect senescence. Of calves that survived to weaning, last-born calves weaned later than earlier-born calves, evidence of terminal investment, a mitigating strategy given reduced reproductive value caused by either components of reproductive senescence.

Long-term studies often rely on natural markings for individual identification across time. The p... more Long-term studies often rely on natural markings for individual identification across time. The primary method for identification in small cetaceans relies on dorsal fin shape, scars and other natural markings. However, dorsal fin markings can vary substantially over time and the dorsal fin can become unrecognizable after an encounter with a boat or shark. Although dorsal fins have the advantage in that they always break the water surface when the cetacean breathes, other physical features, such as body scars and pigmentation patterns can supplement. The goal of this study was to explore the use of dorso-lateral pigment patterns to identify wild bottlenose dolphins. We employed photographic pigment matching tests to determine if pigmentation patterns showed (1) longitudinal consistency and (2) bilateral symmetry using a 30-year photographic database of bottlenose dolphin (Tursiops aduncus). We compared experienced dolphin researchers and inexperienced undergraduate student subjects in their ability to accurately match images. Both experienced and inexperienced subjects correctly matched dolphin individuals at a rate significantly above chance, even though they only had ten seconds to make the match. These results demonstrate that pigment patterns can be used to reliably identify individual wild bottlenose dolphins, and likely other small cetacean species at other sites.

Sex differences in adult behaviour are well documented, but less is known about the ontogeny of t... more Sex differences in adult behaviour are well documented, but less is known about the ontogeny of these differences. In mammals, the transition to independence, from infancy to the juvenile period, is when these sex differences are likely to become prominent. Here, we examined sex differences in behavioural development among calf and juvenile bottlenose dolphins (Tursiops aduncus) from two years pre-weaning to two years post-weaning and whether these differences were consistent, or not, with three non-mutually exclusive hypotheses regarding the function of the juvenile period: the social skills, protection/safety, and energy allocation hypothesis. All hypotheses received some support, but strikingly so for females. First, sex differences in the nature and quality of juvenile social bonds appear to foreshadow adult association patterns. Juveniles had a greater proportion of same-sex associates than calves. Second, although neither sex increased their number of associates from infancy to juvenility, a pattern that might mitigate predation risk, avoidance between juveniles and adult males suggests that both sexes reduce the likelihood of conspecific aggression. This pattern was more marked for juvenile females. Third, females, but not males, increased foraging rates from late infancy to the early juvenile period, even surpassing typical adult female foraging rates. This is likely related to the future energetic demands of maternal investment and skill development required for specialized foraging tactics, which are female biased in this population. This study provides a first step towards understanding the transition into independence for cetaceans, insight into how sex differences develop and a glimpse into the function of the juvenile period.

Network null models are important to drawing conclusions about individual- and population-(or gra... more Network null models are important to drawing conclusions about individual- and population-(or graph) level metrics. While the null models of binary networks are well studied, recent literature on weighted networks suggests that: (1) many so-called ‘weighted metrics’ do not actually depend on weights, and (2) many metrics that supposedly measure higher-order social structure actually are highly correlated with individual-level attributes. This is important for behavioural ecology studies where weighted network analyses predominate, but there is no consensus on how null models should be specified. Using real social networks, we developed three null models that address two technical challenges in the networks of social animals: (1) how to specify null models that are suitable for ‘proportion-weighted networks’ based on indices such as the half-weight index; and (2) how to condition on the degree- and strength-sequence and both. We compared 11 metrics with each other and against null-model expectations for 10 social networks of bottlenose dolphin, Tursiops aduncus, from Shark Bay, Australia. Observed metric values were similar to null-model expectations for some weighted metrics, such as centrality measures, disparity and connectivity, whereas other metrics such as affinity and clustering were informative about dolphin social structure. Because weighted metrics can differ in their sensitivity to the degree-sequence or strength-sequence, conditioning on both is a more reliable and conservative null model than the more common strength-preserving null-model for weighted networks. Other social structure analyses, such as community partitioning by weighted Modularity optimization, were much less sensitive to the underlying null-model. Lastly, in contrast to results in other scientific disciplines, we found that many weighted metrics do not depend trivially on topology; rather, the weight distribution contains important information about dolphin social structure.

Effective foraging is necessary for nearly all animals, but most animals are not born with adult-... more Effective foraging is necessary for nearly all animals, but most animals are not born with adult-like foraging performance. Instead, foraging skills are developed during an individual’s lifetime. Life-history theory predicts that adult-level foraging performance should be reached prior to the start of reproduction, but for most species, we know little about age-specific foraging in the wild. Here, we examine lifetime changes in foraging performance for a group of female wild bottlenose dolphins that use marine sponge tools to forage. After controlling for ecological effects and developmental changes in activity budgets, we show that females continue to improve in 3 aspects of foraging until a peak at around midlife, well after dolphins reach physical and sexual maturity. The factors that lead to this improved performance are unknown, but likely include learning and increasing physical ability. Dolphins’ peak in foraging performance also coincided with a peak in reproduction, with middle-aged females maximizing foraging efficiency and having the highest probability of lactating. Thus, inadequate mastery of foraging behaviors, such as tool use in bottlenose dolphins, does not limit the onset of reproduction, but improvement in foraging skill may help maximize age-specific reproduction and lifetime fitness.

Activity budget data are essential for determining behavioral responses to physiological and ecol... more Activity budget data are essential for determining behavioral responses to physiological and ecological variables. Yet, few studies are available to investigate the robustness, accuracy, and biases of the methods used to estimate activity budgets for cetaceans. In this study, we compare activity budgets of 55 adult female bottlenose dolphins in Shark Bay, Australia derived from two methods: surveys (n = 6,903) and focal follows (n = 1,185, totaling 2,721 h of observation). Activity budgets estimated from survey data differed in all behavioral states compared to focal follow data. However, when controlling for temporal autocorrelation, only time spent socializing and time spent traveling remained disparate between the methods. To control for biases associated with assigning group-level behavior to individuals, we also compared survey and focal follow activity budgets for lone females. Here we found differences between methods in time spent foraging and traveling regardless of whether we controlled for temporal autocorrelation, which suggests detection biases likely play a role in explaining differences in activity budget estimates between the two methodologies. Our results suggest that surveys are less representative of individual-level activity budgets, and thus, when individual-level knowledge about behavior is needed, focal follows are preferred.

Marine Mammal Science, 2013

PloS one, 2010

Background: Molecular tools are now widely used to address crucial management and conservation qu... more Background: Molecular tools are now widely used to address crucial management and conservation questions. To date, dart biopsying has been the most commonly used method for collecting genetic data from cetaceans; however, this method has some drawbacks. Dart biopsying is considered inappropriate for young animals and has recently come under scrutiny from ethical boards, conservationists, and the general public. Thus, identifying alternative genetic collection techniques for cetaceans remains a priority, especially for internationally protected species.

Marine Mammal Science, 2011

To date, color patterns have been used to assess cetacean age and taxonomic status, but few studi... more To date, color patterns have been used to assess cetacean age and taxonomic status, but few studies have determined precise correlates of coloration with known age or investigated its function. Here, we examine the ontogeny of speckling in 88 bottlenose dolphins (Tursiops sp.) in Shark Bay, Australia, of known age, tracked from birth to age 34. Ventral speckles first appear in the genital area at a mean age of 10.2 ± 0.35 yr (range = 7.6-12.7 yr). Throughout their life span, speckles increase in number and density, particularly along the ventral and lateral sides. The timing of speckle onset does not significantly differ by sex but is related to sexual maturity in females. The age of speckle onset in the genital area correlates with the age of first known parturition. In terms of speckle function, we discuss two hypotheses commonly proffered to explain color variation, concealment, and communication. Concealment from predators or prey is unlikely to explain speckle development in Shark Bay Tursiops because the onset occurs long after peak predation risk and initial hunting success (at 3 mo of age). We suggest that speckle patterns offer reliable cues on reproductive status and/or condition and could, thus, serve a communicative or some other function.