A. Catherine Markham

Sex Differences in Wild Chimpanzee Behavior Emerge during Infancy

The role of biological and social influences on sex differences in human child development is a persistent topic of discussion and debate. Given their many similarities to humans, chimpanzees are an important study species for understanding the biological and evolutionary roots of sex differences in human development. In this study, we present the most detailed analyses of wild chimpanzee infant development to date, encompassing data from 40 infants from the long-term study of chimpanzees at Gombe National Park, Tanzania. Our goal was to characterize age-related changes, from birth to five years of age, in the percent of observation time spent performing behaviors that represent important benchmarks in nutritional, motor, and social development, and to determine whether and in which behaviors sex differences occur. Sex differences were found for indicators of social behavior, motor development and spatial independence with males being more physically precocious and peaking in play earlier than females. These results demonstrate early sex differentiation that may reflect adult reproductive strategies. Our findings also resemble those found in humans, which suggests that biologically-based sex differences may have been present in the common ancestor and operated independently from the influences of modern sex-biased parental behavior and gender socialization.

Intergroup conflict: ecological predictors of winning and consequences of defeat in a wild primate population

In many social species, competition between groups is a major factor proximately affecting group-level movement patterns and space use and ultimately shaping the evolution of group living and complex sociality. Here we evaluated the factors influencing group-level dominance among 5 social groups of wild baboons (Papio cynocephalus), in particular focusing on the spatial determinants of dominance and the consequences of defeat. When direct conflict occurred between conspecific baboon groups, the winning group was predicted by differences in the number of adult males in each group and/or groups that had used the areas surrounding the encounter location more intensively than their opponent in the preceding 9 or 12 months. Relative intensity of space use over shorter timescales examined (3 and 6 months) was a poor predictor of the interactions outcome. Losing groups but not winning groups experienced clear short-term costs. Losing groups used the area surrounding the interaction less following an agonistic encounter (relative to their intensity of use of the area prior to the interaction). These findings offer insight into the influences and consequences of intergroup competition on group-level patterns of space use.

Remote Monitoring of Primates Using Automated GPS Technology in Open Habitats

Automated tracking using a satellite global position system (GPS) has major potential as a research tool in studies of primate ecology. However, implementation has been limited, at least partly because of technological difficulties associated with the dense forest habitat of many primates. In contrast, primates inhabiting relatively open environments may provide ideal subjects for use of GPS collars, yet no empirical tests have evaluated this proposition. Here, we used an automated GPS collar to record the locations, approximate body surface temperature, and activity for an adult female baboon during 90 days in the savannah habitat of Amboseli, Kenya. Given the GPS collars impressive reliability, high spatial accuracy, other associated measurements, and low impact on the study animal, our results indicate the great potential of applying GPS technology to research on wild primates. Am. J. Primatol. 70:495–499, 2008.

SALINITY AND POPULATION PARAMETERS OF BALD EAGLES (HALIAEETUS LEUCOCEPHALUS) IN THE LOWER CHESAPEAKE BAY

Abstract We evaluated the relationship between salinity and Bald Eagle (Haliaeetus leucocephalus) population parameters using 26 years of survey data for the lower Chesapeake Bay. Tidal tributaries within the study area were stratified according to the Chesapeake Bay Programs segmentation scheme, and segments with the same salinity classification were considered spatial replicates. Salinity categories included tidal fresh, oligohaline, mesohaline, and polyhaline. Four parameters— colonization rate, nesting density, projected carrying capacity, and productivity— were derived from nesting data within each shoreline segment and compared across the salinity gradient. The study-wide Bald Eagle population is exhibiting exponential growth, with an average doubling time of 7.9 years. All population parameters showed significant directional variation with salinity. Average population doubling time for tidal fresh reaches was <6 years, compared with >16 years for polyhaline areas. Current Bald Eagle nesting density is negatively related to salinity and varies by a factor of 4 across the gradient. Comparison of current densities with projected carrying capacity suggests that these differences will be stable or increasing as the geographic areas approach equilibrium densities. We suggest that fisheries within lower saline reaches, including spring spawning runs of anadromous Clupeidae (shad and herring), are the most likely explanation for salinity effects. Observed distribution patterns suggest that lands along low-salinity waters are the core of the Bald Eagle nesting population within the lower Chesapeake Bay and should be the focus of long-term programs designed to benefit nesting eagles. Salinidad y Parámetros Poblacionales de Haliaeetus leucocephalus en la Bahia de Chesapeake

Optimal group size in a highly social mammal

Significance What are the costs and benefits for animals living in groups of different sizes? Balancing the trade-offs between within-group competition (which favors smaller groups) and between-group competition (which favors larger groups) suggests that intermediate-sized groups may be best, yet empirical support for this prediction has largely been lacking. Using long-term data on wild baboons, we provide novel evidence that individuals living in intermediate-sized groups have energetically optimal space-use strategies and lower glucocorticoid (stress hormone) concentrations than individuals in either large or small groups. Our results offer new insight into the costs and benefits of group living. Group size is an important trait of social animals, affecting how individuals allocate time and use space, and influencing both an individual’s fitness and the collective, cooperative behaviors of the group as a whole. Here we tested predictions motivated by the ecological constraints model of group size, examining the effects of group size on ranging patterns and adult female glucocorticoid (stress hormone) concentrations in five social groups of wild baboons (Papio cynocephalus) over an 11-y period. Strikingly, we found evidence that intermediate-sized groups have energetically optimal space-use strategies; both large and small groups experience ranging disadvantages, in contrast to the commonly reported positive linear relationship between group size and home range area and daily travel distance, which depict a disadvantage only in large groups. Specifically, we observed a U-shaped relationship between group size and home range area, average daily distance traveled, evenness of space use within the home range, and glucocorticoid concentrations. We propose that a likely explanation for these U-shaped patterns is that large, socially dominant groups are constrained by within-group competition, whereas small, socially subordinate groups are constrained by between-group competition and predation pressures. Overall, our results provide testable hypotheses for evaluating group-size constraints in other group-living species, in which the costs of intra- and intergroup competition vary as a function of group size.

Finfish-Waterbird Trophic Interactions in Tidal Freshwater Tributaries of the Chesapeake Bay

Abstract With the DDT ban enacted in the early 1970s, piscivorous bird populations have grown exponentially throughout the tidal reach of the Chesapeake Bay. However, avian population growth is not uniform throughout the Chesapeake Bay watershed; several species including Bald Eagles (Haliaeetus leucocephalus) and Ospreys (Pandion haliaetus) experienced significantly greater population growth rates in riverine tidal freshwater and oligohaline regions than in higher salinity portions of the bay. Shifting fish prey resources may provide an explanation for the observed influence of salinity on distribution of piscivorous bird populations. Changes in the fish resources available to avian predators over the past 40 years include changing temporal and spatial distribution of fish prey, as well as shifts in taxonomic and trophic structure of resident and migratory fish assemblages. Historical ecological changes, including long- and short-term changes in the abundance of anadromous clupeid fishes, Atlantic Menhaden (Brevoortia tyrannus), and the relatively recent introduction and establishment of non-indigenous fishes, within tidal freshwater rivers may be influencing piscivorous bird distributions and abundance, particularly for Bald Eagles and Ospreys, in the Chesapeake Bay. Predator-prey interactions among piscivorous birds and fish prey have received little attention from wildlife managers. Collaborative efforts between fishery scientists and avian ecologists will ultimately lead to better ecosystem management of the Bay’s living resources.

Documentation of Infanticide and Cannibalism in Bald Eagles

DOCUMENTACION DE INFANTICIDIO Y CANIBALISMO EN HALIAEETUS LEUCOCEPHALUS Aunque el infanticidio de individuos no emparentados y el canibalismo estan bien documentados para varias especies de aves, las observaciones directas de este comportamiento en las aves rapaces son relativamente escasas. Describimos un caso de infanticidio y canibalismo en Haliaeetus leucocephalus. En este caso, el macho residente adulto desaparecio poco despues de que el pichon eclosiono, y la hembra asumio las responsibilidades de la crianza sin ayuda hasta que el nido fracaso. La primera instancia de canibalismo tuvo lugar cuando el mas joven de los tres pichones murio y fue entregado como alimento a sus hermanos por la madre. Otros actos de canibalismo se presentaron luego de la occurrencia de infanticidio, cuando un macho de cuatro anos de edad entro al nido matando y consumiendo a los dos pichones restantes. Sugerimos que estos eventos de infanticidio y canibalismo estuvieron estrechamente ligados a la desaparicion del macho res...

The Influence of Salinity on the Diet of Nesting Bald Eagles

ABSTRACT Although the breeding density of Bald Eagles (Haliaeetus leucocephalus) in the lower Chesapeake Bay is known to vary with salinity, the ecological factors that contribute to this distribution have not been explored. In an effort to examine whether variation in prey use is associated with nest density patterns, we investigated the influence of salinity (tidal-fresh vs. mesohaline zones) on Bald Eagle diet composition by using video-monitoring to observe food delivered to nests during the 2002–2003 breeding seasons. Delivered prey items were identified to the lowest taxonomic level possible and sizes were estimated relative to eagle bill length. We used species-specific length-weight relationships for prey to estimate biomass delivery. Overall, the diet included at least 12 species of fishes, three species of birds, four species of mammals, and four species of reptiles. Salinity had no significant influence on diet composition; Ictaluridae and Clupeidae species were the most frequent prey items in both salinity zones. We suggest that pairs nesting in both tidal-fresh and mesohaline zones have access to similar fish species. However, the length and biomass of fish prey varied with salinity such that larger prey on average were delivered to nests in the mesohaline reaches compared to tidal-fresh zones. Thus, we suggest that foraging eagles may be exploiting more energetically-favorable conditions in higher salinity waters. Temporally, diet composition varied between study years, potentially reflecting annual changes in the availability of prey species. We consider differences in weather patterns between study years as the most likely factor contributing to this interannual variation in diet.

Reproductive state and rank influence patterns of meat consumption in wild female chimpanzees (Pan troglodytes schweinfurthii).

An increase in faunivory is a consistent component of human evolutionary models. Animal matter is energy- and nutrient-dense and can provide macronutrients, minerals, and vitamins that are limited or absent in plant foods. For female humans and other omnivorous primates, faunivory may be of particular importance during the costly periods of pregnancy and early lactation. Yet, because animal prey is often monopolizable, access to fauna among group-living primates may be mediated by social factors such as rank. Wild chimpanzees (Pan troglodytes) across Africa habitually consume insects and/or vertebrates. However, no published studies have examined patterns of female chimpanzee faunivory during pregnancy and early lactation relative to non-reproductive periods, or by females of different rank. In this study, we assessed the influence of reproductive state and dominance rank on the consumption of fauna (meat and insects) by female chimpanzees of Gombe National Park, Tanzania. Using observational data collected over 38 years, we tested (a) whether faunivory varied by reproductive state, and (b) if high-ranking females spent more time consuming fauna than lower-ranking females. In single-factor models, pregnant females consumed more meat than lactating and baseline (meaning not pregnant and not in early lactation) females, and high-ranking females consumed more meat than lower-ranking females. A two-factor analysis of a subset of well-sampled females identified an interaction between rank and reproductive state: lower-ranking females consumed more meat during pregnancy than lower-ranking lactating and baseline females did. High-ranking females did not significantly differ in meat consumption between reproductive states. We found no relationships between rank or reproductive state with insectivory. We conclude that, unlike insectivory, meat consumption by female chimpanzees is mediated by both reproductive state and social rank. We outline possible mechanisms for these patterns, relate our findings to meat-eating patterns in women from well-studied hunter-gatherer societies, and discuss potential avenues for future research.

The Influence of Salinity on Provisioning Rates and Nestling Growth in Bald Eagles in the Lower Chesapeake Bay

Abstract We measured provisioning and growth patterns in Bald Eagle (Haliaeetus leucocephalus) chicks from nests in two salinity zones in the lower Chesapeake Bay. Nestlings in mesohaline reaches experienced higher per capita consumable energy provisioning rates and had higher instantaneous growth rates compared to nestlings in tidal-fresh salinity zones. These results suggest that Bald Eagles nesting along mesohaline reaches are more successful at meeting the energetic demands of brood rearing compared to pairs nesting along tidal-fresh reaches, a finding consistent with documented higher reproductive rates and proportion of three-chick broods along mesohaline reaches compared to tidal-fresh reaches. The results of this study have important conservation implications for Bald Eagles by addressing issues related to variation in habitat quality within a continuous ecosystem and the determination of core breeding zones.