In order to prevent species extinctions, conservation strategies need to incorporate the identification and mitigation of the root causes of population decline with an assessment of vulnerability to genetic and stochastic factors affecting small populations. Species or populations with small ranges, such as those on islands, are particularly vulnerable to extinction, and deficient knowledge of these species often impedes conservation efforts. The Bahama Swallow (Tachycineta cyaneoviridis) is an endangered secondary cavity-nester that only breeds on three islands in the northern Bahamas: Abaco, Grand Bahama, and Andros. I investigated questions related to population size and distribution, genetic diversity and population structure, breeding biology, and ecological interactions of the swallow, with the goal of informing the conservation and management of the species. Using several population survey methods on Abaco, I found that swallow site occupancy and density is higher in southern Abaco, especially near roads and pine snags. Future research should prioritize identifying the causes of variable and low population densities in parts of the swallow's range. I used microsatellite markers and morphometrics to assess differences between populations on Abaco and Andros. We found a lack of genetic differentiation (G'ST = 0.03) between populations, but differences in morphology suggest that gene flow might be low enough to enable traits under selection to diverge. By locating and monitoring nests, I found that swallows rely on woodpecker-excavated cavities in pine snags and utility poles, and that swallows nesting in pine snags had higher fledging success (92%) than those nesting in utility poles (50-62%). Using a cavity nest-web approach, I assessed how swallows interact with cavity-nesting birds and resources on Abaco. Hairy Woodpeckers (Dryobates villosus) primarily excavated pine snags, while West Indian Woodpeckers (Melanerpes superciliaris) excavated utility poles in non-pine habitat. Only swallows and La Sagra's Flycatchers (Myiarchus sagrae) used nest sites in the pine forest. Swallows in non-pine habitat face competition for cavities with American Kestrels (Falco sparverius), and non-native House Sparrows (Passer domesticus) and European Starlings (Sturnus vulgaris). These results highlight the importance of pine forest and the Hairy Woodpecker for the persistence of the swallow. / Doctor of Philosophy / In order to prevent species extinctions, conservation strategies need to identify and resolve the problems that cause species to decline, as well as address issues characteristic of small populations. Species or populations with small ranges, such as those on islands, are particularly vulnerable to extinction, and lack of knowledge of these species often impedes conservation efforts. The Bahama Swallow is an endangered species that only breeds on three "pine islands" in the northern Bahamas. The swallow is a secondary cavity-nester, which means that it nests in a cavity, usually either a natural tree hole or a hole created by another bird species. In this study, I investigated where swallows are found on the islands, the genetics and body sizes of populations, nesting biology, and connections with other species, with the goal of providing information for the conservation and management of the species. On Abaco, I found that there are more swallows in the southern part of the island, especially near roads and the dead standing pine trees (pine snags) used for nesting. Future research should assess why there are fewer birds in other parts of the swallow's range. I tested whether the genetics and body sizes of populations on Abaco and Andros are different from each other. Populations were genetically similar, but may be separated enough to result in body size differences. I located swallow nests on Abaco, and found that swallows rely on cavities made by woodpeckers in pine snags and utility poles. By visiting some nests repeatedly, I found that swallows nesting in pine snags were more successful than those nesting in utility poles. I also assessed how swallows interact with the other bird species that create and use nesting cavities. Hairy Woodpeckers usually create cavities in pine snags, while West Indian Woodpeckers use utility poles outside of the pine forest. Swallows nesting in the pine forest compete with fewer bird species for cavities than swallows nesting in other habitats. These results show that managing the forest to retain pine snags and Hairy Woodpeckers is important for the conservation of the swallow.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/96264 |
| Date | 02 January 2020 |
| Creators | Wilson, Maya |
| Contributors | Biological Sciences, Walters, Jeffrey R., Catlin, Daniel H., Karpanty, Sarah M., Mims, Meryl C., McGlothlin, Joel W. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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