Browsing by Subject "Behavioral ecology"

Studies of the social behavior of Cuvier’s beaked whales (Ziphius cavirostris) are challenging because of their pelagic habitat and the limited time they spend at the surface. The sociality of these deepest diving mammals is of great interest, however, including how social behavior might influence responses to anthropogenic disturbance as this species has a history of stranding in association with certain types of human-created noise. Beyond conservation concerns, the beaked whales (Family Ziphiidae) are a valuable group for the comparative study of the ecological influences on mammalian social evolution since they are an “out group within an out group”, including some of the most extreme diving mammals within the Cetacea which are themselves one of the few mammalian groups to become secondarily fully aquatic. The beaked whales are also the second most speciose family in the cetaceans and so can lend statistical power to formal comparative analyses. One unifying characteristic of most beaked whale species is sexually dimorphic dentition, where only adult males have erupted tusks which they appear to use as weapons in contests with each other as evidenced by the high level of scarring in adult males. Despite this, previous studies suggest a substantial amount of variation in beaked whale social structure and mating systems.

In this work, I investigated the social behavior of a relatively accessible, high density population of Cuvier’s beaked whales off the coast of Cape Hatteras, North Carolina, USA. I used data from photo identification surveys from a longitudinal study, as well as satellite-linked depth-recording telemetry tags to investigate within and between group behavior. In addition, I present a case study and assessment of how I optimized the programming of telemetry instruments to increase their value in behavioral studies.

I tested the stability of adult male-male interactions over the medium term using diving synchrony as a proxy for group membership and found that adult male-male pairs stayed remarkably synchronous for days to weeks, contrary to expectations that individuals would quickly competitively exclude each other. Using photo-identification records of whole groups, I did not find strong evidence for sexual segregation and instead found a high level of fission-fusion behavior between groups. In addition, I did not find strong evidence for long term stable group formations, although given the large population size and a relatively small sample size infrequent but important bonds among individuals may have been missed. Using a new programming regime to collect up to 14 days of time-series depth data on an individual, I was able to confirm that diel differences in dive depth were almost entirely explained by bouts of shallow diving which occur only a night. These shallow dives appear to be a separate mode of diving behavior not previously well described in the literature, and although this behavior may have multiple functions, it may be a useful behavioral modality to investigate further in relation to social behavior.

Finally, I argue that the application of similar methods used here combining photo-identification and telemetry tagging could lead to rapid discovery of social parameters in other hard to study pelagic Cetaceans including other Ziphiidae with a view toward building a comparative dataset.

The ultimate goal of wildlife recovery is abundance growth of a species, though it must also involve the reestablishment of the species’ ecological role within ecosystems frequently modified by humans. Reestablishment and subsequent recovery may depend on the species’ degree of adaptive behavior as well as the duration of their functional absence and the extent of ecosystem alteration. In cases of long extirpations or extensive alteration, successful reestablishment may entail adjusting foraging behavior, targeting new prey species, and encountering unfamiliar predatory or competitive regimes. Recovering species must also increasingly tolerate heightened anthropogenic presence, particularly within densely inhabited coastal zones. In recent decades, gray seals (Halichoerus grypus) recovered from exploitation, depletion, and partial extirpation in the Northwest Atlantic. On Cape Cod, MA, USA, gray seals have reestablished growing breeding colonies and seasonally interact with migratory white sharks (Carcarodon carcharias). Though well-studied in portions of their range due to concerns over piscivorous impacts on valuable groundfish, there are broad knowledge gaps regarding their ecological role to US marine ecosystems. Furthermore, there are few studies that explicitly analyze gray seal behavior under direct risk of documented shark predation.

In this dissertation, I apply a behavioral and movement ecology approach to telemetry data to understand gray seal abundance and activity patterns along the coast of Cape Cod. This coastal focus complements extensive research documenting and describing offshore movement and foraging behavior and allows me to address questions about movement decisions and risk allocation. Using beach counts of seals visible in satellite imagery, I estimate the total regional abundance of gray seals using correction factors from haul out behavior and demonstrate a sizeable prey base of gray seals locally. Analyzing intra-annual space use patterns, I document small, concentrated home ranges utilizing nearshore habitats that rapidly expand with shifting activity budgets to target disperse offshore habitats following seasonal declines in white sharks. During the season of dense shark presence, seals conducted abbreviated nocturnal foraging trips structured temporally around divergent use of crepuscular periods. The timing of coastal behavior with different levels of twilight indicate risk allocation patterns with diel cycles of empirical white shark activity. The emergence of risk allocation to explain unique behavioral and spatial patterns observed in these gray seals points to the importance of the restored predator-prey dynamic in gray seal behavior along Cape Cod.

Sexual conflict occurs when female and male fitness interests diverge. In a social system characterized by aggressive sexual coercion and the risk of infanticide, female chimpanzees (Pan troglodytes) respond to this conflict by exhibiting an exaggerated sexual swelling that advertises sexual receptivity while concealing the exact timing of ovulation. Sexual swellings impose significant costs, yet can persist into pregnancy. Records from long-term studies of eastern chimpanzees (P. t. schweinfurthii) in Gombe National Park, TZ, and Kibale National Park, UG, provide data on postconception swellings, while data on group composition and behaviors such as mating, grooming, and aggression are drawn from the Gombe database only. Throughout, I use linear mixed models to simultaneously test multiple effects while controlling for repeated measures of individuals. In Chapter 1, I tested whether variation in females’ vulnerability to infanticide and aggression predicted the amount of swelling during pregnancy. In Chapter 2, I examined female-male relationships across reproductive states to ask whether females can better gain benefits and avoid costs by affiliating promiscuously with all males, or by investing in relationships with preferred males. Finally, I analyzed metabolites of reproductive hormones using urine samples from pregnant females in both populations to build a hormonal profile of postconception swellings. Swellings during pregnancy increase female-male association, and are caused by the same basic hormonal mechanism as preconception swellings, though they occur in a very different hormonal milieu. Females at greater risk of infanticide and intrasexual aggression swell more during pregnancy. Females mate promiscuously before conception, but during pregnancy and lactation, preferentially groom with males that are likely to protect them from aggression and infanticide. Based on these and other findings, I conclude that postconception swellings in chimpanzees are an adaptive response to sexual conflict.