| dc.description.abstract | Behavioral changes are necessary for an individual to adjust to the environment to avoid fitness loss and death. Understanding how behaviors change based on environmental cues is important in their local management and supports conservation. Therefore, the dissertation has focused on how environmental conditions influence behavioral changes.
The first chapter investigated the flocking behaviors of a wintering passerine in Oklahoma. Birds often aggregate into more dense groupings during nonbreeding than breeding periods. This includes large flocks of wintering grassland birds, such as the Chestnut-collared Longspur (Calcarius ornatus). Understanding what drives flocking behavior in the nonbreeding period is essential for guiding their management. The spatial scale at which membership flocks remain consistent can inform the management of the winter habitats of these migrant birds. Therefore, the first chapter focused on the social behaviors of wintering Chestnut-collared Longspurs in Oklahoma. We captured and tracked individual longspurs during two winters between 2018 and 2020 and analyzed their social network structure. We found that this population consistently clustered into social communities rather than being associated with resource clustering alone. In the winter seasons we studied, 66.1% (2018-19) and 92.5% (2019-20) of individuals had associations solely within their community, while 33.3% (2018-19) and 7.5% (2019-20) of individuals had at least 60% of their associations within the community. The number of associations an individual experienced did not depend on sex or age. Since Chestnut-collared Longspurs occur in flocks in winter, managers should consider the spatial requirements of flocks, ranging from 38.3ha to 2468.4ha, rather than individual spatial requirements. Apparent thresholds for flock cohesion in the species differ across years and are likely driven by the availability of resources, such as seeds and surface water, rather than individual spatial requirements.
The second chapter investigated the activities of a wintering passerine around a standing livestock pond using automated telemetry, which monitored marked birds’ presence in the vicinity of the pond. We used Chestnut-collared Longspur as the study species because they are often detected visiting open water sources in grasslands. We captured adult Chestnut-collared Longspurs (Calcarius ornatus) from January to March 2021 at Rita Blanca National Grasslands and attached solar-powered radio tags (“Life tags”). Node units installed around the pond detected radio-tagged birds. We analyzed their activity in the vicinity of the pond relative to weather conditions (e.g., Overnight minimum dewpoint temperature, dewpoint temperature at sunrise, wind speed, and day length). Our results imply that Chestnut-collared Longspurs adjust their daily activity in response to environmental conditions to balance their water needs with water accessibility. The timing of the first visit depended on the overnight minimum dewpoint temperature and dewpoint temperature at sunrise. The first detection of the bird in the vicinity of the pond occurred significantly earlier when the overnight minimum dewpoint temperature was below -15.86°C (cold and dry conditions). However, if dewpoint temperature at sunrise was below -7.2°C, the first visit was delayed until surface water is likely to be available. The number and duration of daily visits changed across the winter season. As birds approached migration, they increased the number of shorter visits to the pond, leading to an overall increase in total duration spent in the vicinity of the pond.
The third chapter focused on the distribution of Yellow-eared bulbul in Sri Lanka. Species’ distributions may change in response to climate change as individuals seek to remain within preferred climatic niches. Migration options for island mountain species such as the Sri Lankan-endemic Yellow-eared bulbul (Pycnonotus penicillatus) may be limited. Considering the uncertain future this presents for the species, we used the correlative habitat suitability model Maxent to parameterize Yellow-eared Bulbul’s current climate niche and project its range shifts under three global climate change models (CNRM-C6, CNRM-ESM-2, and MIROC5), specifically scenario ‘SSP126’ every 20 years from 2030-2090. Our models fit each of two inter-monsoonal breeding seasons (area under curve > 0.95), with variation best explained by mean temperature of the driest quarter and minimum temperature of the coldest month. Relative to current distributions, our models predicted that the highly suitable Yellow-eared Bulbul niche area would increase by 10.1% by 2030 but decrease by 14.8% by 2070. This would coincide with a northward shift of suitable niche space, with severely reduced populations in the southwestern Sinharaja area. Although climatically suitable habitats in Sri Lanka are not projected to disappear by 2090, this does not guarantee Yellow-eared Bulbul’s future. Its northward migration cannot continue indefinitely on this island nation, and areas of putatively suitable climates may not have necessary habitat characteristics (e.g., canopy height or species diversity). Therefore, although Yellow-eared Bulbul may not be immediately imperiled by climate change, it may have limited abilities to adapt and persist without pre-emptive habitat management.
Keywords: Spatial, Winter, Passerines, Sri Lanka | en_US |
