Biology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2749
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Item MOVING THE GOALPOSTS: MIGRATORY BIRDS IN A CHANGING WORLD(2023) Nemes, Claire E.; Cohen, Emily B; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Billions of birds undertake migratory movements each year, traveling distances that range from several hundreds to tens of thousands of kilometers. Migratory birds must be flexible enough to cope with the fluctuating conditions they encounter during these journeys and at their destinations. However, humans are rapidly and dramatically changing the environment across all portions of migratory species’ ranges through habitat destruction and conversion, introduction of invasive species, climate change, and other alterations. My dissertation research seeks to understand the constraints and threats facing birds during two understudied phases of the annual cycle: migration and the non-breeding stationary period. In Chapter 1, I explore how human activities may nonlethally affect birds during migration. I reviewed the scientific literature for evidence of nonlethal effects and of interacting threats that may compound fitness costs to migrating birds. In general, I found that scientific understanding of nonlethal effects during migration lags behind research on direct mortality. Because birds migrate through increasingly anthropogenic landscapes and airspaces, I identify this knowledge gap as a hindrance to effective conservation of migratory birds. In Chapter 2, I investigate if individual songbirds adjust the rate and timing of spring migration based on the vegetation phenology they encounter within North America which may allow them to keep pace with advancing spring phenology under climate change. In the spring, migrating birds must quickly reach their breeding grounds to secure territories and mates ahead of the competition, but individuals that arrive too early may encounter inclement weather or food shortages. Using the Motus automated radio telemetry network, I tracked individual songbirds as they traveled from the southern U.S. towards their breeding areas in spring. I used estimates of spring onset timing at different points on their migration routes to determine if birds traveled in sync with the “green wave” of emerging vegetation or if they used a different strategy. I found that birds migrating from their non-breeding areas arrived in the southern U.S. well after local spring onset, but were able to catch up to the wave of emerging spring vegetation as they traveled northwards, following a “catching up” strategy rather than a “surfing” one. In Chapter 3, I examine how individual songbirds respond to the threat of predation during migratory stopover, when they must balance conflicting demands of refueling and avoiding predators. Migrating birds must contend with both native avian predators such as hawks (Accipiter sp.) and abundant introduced predators such as free-roaming domestic cats (Felis catus), yet their behavioral responses to cats have been little studied during migration. Using an aviary experiment, I exposed wild Gray Catbirds Dumetella carolinensis to either a hawk or a domestic cat and observed their behaviors before and after exposure to determine if they responded appropriately to the threat posed by each predator. When compared with a control group, Catbirds responded differently to both types of predators in the short term, but I detected no differences in their behavior after release. This study provides novel insights into the possible nonlethal effects of introduced predators that birds may encounter during migration. In Chapter 4, I shift focus to explore the threat that free-roaming domestic cats pose to birds in the Caribbean within a Neotropical city. Urban regions are increasingly recognized to provide valuable wildlife habitat but may also contain hazards such as introduced predators, and we currently lack information on the effects of free-roaming cats on migratory and resident bird species during non-breeding seasons. I designed a camera trapping project in San Juan, Puerto Rico to estimate free-roaming cat densities across a gradient of urbanization as a step towards understanding their potential impacts on wildlife. I deployed cameras across 16 trapping grids at three levels of urbanization and used photographic captures of cats to build spatial capture-recapture models. Estimated cat densities ranged from 48 8 (SE) cats/km2 in exurban areas to 473 40 cats/km2 in the most heavily urbanized parts of the city. These data may prove useful for conservation practitioners in San Juan deciding where to target cat management efforts for the benefit of urban wildlife and public health.Item SOCIAL STRUCTURE OF ASIAN ELEPHANTS (ELEPHAS MAXIMUS) IN SRI LANKA(2015) Samy, Julie Marie; Wilkinson, Gerald S; Thompson, Katerina; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Asian elephants (Elephas maximus) are critically endangered and live in fragmented populations spread across 13 countries. Yet in comparison to the African savannah elephant (Loxodonta africana), relatively little is known about the social structure of wild Asian elephants because the species is mostly found in low visibility habitat. A better understanding of Asian elephant social structure is critical to mitigate human-elephant conflicts that arise due to increasing human encroachments into elephant habitats. In this dissertation, I examined the social structure of Asian elephants at three sites: Yala, Udawalawe, and Minneriya National Parks in Sri Lanka, where the presence of large open areas and high elephant densities are conducive to behavioral observations. First, I found that the size of groups observed at georeferenced locations was affected by forage availability and distance to water, and the effects of these environmental factors on group size depended on site. Second, I discovered that while populations at different sites differed in the prevalence of weak associations among individuals, a core social structure of individuals sharing strong bonds and organized into highly independent clusters was present across sites. Finally, I showed that the core social structure preserved across sites was typically composed of adult females associating with each other and with other age-sex classes. In addition, I showed that females are social at all life stages, whereas males gradually transition from living in a group to a more solitary lifestyle. Taking into consideration these elements of Asian elephant social structure will help conservation biologists develop effective management strategies that account for both human needs and the socio-ecology of the elephants.Item ECOLOGY AND DEMOGRAPHY OF GOLDEN-HEADED LION TAMARINS (Leontopithecus chrysomelas) IN CABRUCA AGROFOREST, BAHIA STATE, BRAZIL.(2010) Oliveira, Leonardo de Carvalho; Dietz, James M; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Understanding how species use the matrix of habitat that surrounds forest fragments can contribute to conservation strategies in fragmented landscapes. In this dissertation, I evaluate the effects of habitat structure and resource availability on group characteristics, use of space, and predation risk for the endangered golden-headed-lion tamarins in shaded cocoa plantations locally known as cabruca agroforest. In the first chapter I present a list of tree species that provide key foods and sleeping sites used by lion tamarins. Families Myrtaceae and Sapotaceae are the most commonly used by lion tamarins for both food and sleeping sites. Fifty-five tree species were ranked as extremely valuable for the tamarins. Cabruca management that retains the species listed in this study may improve the long-term survival of lion tamarins. In the second chapter, I compare ecological and demographic data of lion tamarins in cabruca and other vegetation types. In contrast with my prediction that food resources would be scarce in cabruca, the exotic and invasive jackfruit (Artocarpus heterophyllus) was an abundant food resource for tamarins in cabruca while bromeliads were the favorite substrate for animal prey foraging. Group size and composition were similar in all vegetation types. Males in cabruca were heavier than those in primary forest. Density of lion tamarins in cabruca was the highest and home range size the smallest reported for the species. This is the first study to show that lion tamarins can live and reproduce exclusively in cabruca and has important implications for conservation of the species. In my third chapter, I test two hypotheses explaining the association between lion tamarins and Wied's marmoset (Callithrix kuhlii): foraging benefits and predation avoidance. I found no evidence to support the hypothesis that interspecific associations provide foraging benefits for lion tamarins. However, several findings support the predation avoidance hypothesis: associations occurred in areas where predation risk was higher, and during the part of the day in which predation risk was highest, and following birth events when the tamarins were more susceptible to predation. Despite the importance of cabruca to lion tamarins, they are more exposed to predation in this habitat.Item Elucidating the Macro- and Micro-evolutionary Relationships of the Federally Listed Endangered Species Agalinis acuta (Orobanchaceae)(2010) Pettengill, James Beaton; Neel, Maile C; Behavior, Ecology, Evolution and Systematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Agalinis acuta (Orobanchaceae) is a federally listed endangered plant species native to the mid-Atlantic and northeastern coastal plains of the United States. Due to morphological ambiguity and molecular similarity between A. acuta and Agalinis tenella and Agalinis decemloba a conservation priority is to determine whether A. acuta represents an evolutionarily distinct entity worthy of protection under the Endangered Species Act. To resolve this question, a phylogenetic study was first conducted based on seven chloroplast DNA loci and the nuclear DNA locus ITS from 79 individuals representing 29 Agalinis species. A study evaluating the utility of those cpDNA loci and three analytical techniques for the purpose of DNA barcoding was also conducted. The phylogenetic study indicated that A. acuta was perhaps evolutionarily indistinct from A. decemloba and A. tenella. Based on the results of subsequent analyses of 21 microsatellite loci and morphological data evaluated under myriad species concepts, A. acuta, A. decemloba, and A. tenella best represent a single species with two subspecies; the former two putative species would constitute a subspecies called A. decemloba ssp. decemloba and A. tenella would be A. decemloba ssp. tenella. With evolutionary distinct entities described, a phylogeographic study was conducted to determine the extent to which historical processes rather than contemporaneous events can explain extant patterns of genetic and phenotypic diversity within A. decemloba. The dispersal of a few individuals out of southern refugial populations likely represents the process through which northern populations were established; however, recent anthropogenic effects that disproportionately affected northern populations may have also contributed to extant patterns of diversity. Neutral or adaptive explanations for phenotypic variation among populations are also investigated. The conservation implications of population genetic analyses were assessed for members of A. decemloba ssp. decemloba. Despite the evidence that this taxon is self-compatible, the high levels of inbreeding and low levels of heterozygosity are of such a magnitude in certain populations that genetic factors may be negatively impacting fitness. Because of the small effective population sizes and degree of isolation, all populations should be managed to reduce the risk of extinction associated with demographic and environmental stochasticity.Item MATRIX EFFECTS ON INDIVIDUAL AND COMMUNITY-LEVEL RESPONSES OF BIRDS TO FOREST FRAGMENTATION IN JAMAICA(2009) KENNEDY, CHRISTINA MARIE; Neel, Maile C; Fagan, William F; Behavior, Ecology, Evolution and Systematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Land cover between habitat patches ("matrix") can impact species persistence in fragmented landscapes by altering resource availability, edge effects, or inter-patch movement. This thesis examines how the matrix affects the Neotropical bird community in central Jamaica in landscapes where forest is embedded in three human-dominated matrix types (agriculture, peri-urban development, and bauxite mining) and one natural "matrix" (continuous forest). First, I examine whether richness, community composition, and abundances of resident birds differ in ~100 forest patches within the four matrix types, and relate species responses to traits influencing dispersal, resource acquisition, and/or population growth. Agricultural landscapes were found to retain avian diversity and community assemblages most similar to intact forest relative to peri-urban and bauxite landscapes. Traits related to resource acquisition best predicted species responses, indicating that resource limitation driven by the matrix may be a primary factor driving bird responses to fragmentation. Next, I determine the relative influence of patch area, isolation, vegetation structure, and matrix type on the occupancy dynamics of resident insectivorous birds. Within-patch vegetation and matrix type were the most important determinants of colonization and extinction, but the effects of patch area, isolation, and vegetation on occupancy dynamics were matrix- and species-dependent. Across the community, the matrix influenced extinction probabilities more than colonization, indicating that extinction processes likely drive population dynamics. Finally, I examine the relative permeability of peri-urban, bauxite, and forested landscapes on the movement of the migrant American Redstart (Setophaga ruticilla) and the resident Jamaican Tody (Todus todus) by experimentally translocating > 140 birds 0.6-4 km from their territories across landscape treatments. Redstarts returned with greater success and faster speed than Todies. Return success was not impacted by landscape treatment, but both species returned more rapidly in forest relative to bauxite matrix, with return times intermediate in a peri-urban matrix. These findings indicate that bird mobility in fragmented landscapes is mediated by the landscape matrix. This research is among few empirical studies to discern the impacts of different matrix types on species patterns and processes. These results inform theory on fragmentation as well as bird conservation in an understudied system.