Master of Science (MS)
Semester of Degree Completion
Jill L. Deppe
Chapter I. Full-service hotels, convenience stores or fire escapes? Evaluating function of stopover sites for Neotropical migrants in the northern Yucatan Peninsula
Nearctic-Neotropical migratory songbirds incur the highest mortality rates during their annual migrations. Migratory songbirds use a network of stopover sites to rest, refuel, or seek refuge during times of poor weather conditions; and the time and energy expended at these sites exceeds that of migratory flight. In order to conserve stopover sites with the highest value to Neotropical migrants, a conceptual framework was developed to classify stop over sites into three functional categories based on their function for migratory landbirds, but there have been few attempts to empirically validate this framework. We evaluated the stopover site conservation framework using two protected areas hypothesized to lie at opposite ends of the framework. We use capture data and radio-tracking data to examine patterns in daily capture rates, body condition, rates of mass gain, stopover duration, and departure behavior with a focus on four species; Swainson's Thrush (Catharus ustulatus), Red-eyed Vireo (Vireo olivaceus), Gray Catbird (Dumetella carolinensis), and Prothonotary Warbler (Protonotaria citrea). Our results indicate that variance in daily capture rates, energetic condition, and rates of mass gain are reliable metrics by which to evaluate stopover site function for migratory landbirds. In addition to these metrics, departure direction may provide additional information regarding landscape-scale stopover site use by migratory landbirds. This conservation framework should be used to facilitate stopover site conservation for Neotropical migratory songbirds, and can be applied at sites in the United States as well as tropical regions.
Chapter II. Coastal habitat use by four species of migratory songbird at a stopover site in the Northern Yucatan Peninsula, Mexico
Migratory songbirds use a network of stopover sites along their migratory routes to rest, refuel, and replenish lost energy reserves. In order for songbirds to quickly refuel and acquire sufficient energy for the next leg of their migration, birds must find suitable stop over sites that provide necessary food, shelter, and safety. Determining en-route habitat quality is particularly challenging, as birds use multiple unfamiliar sites distributed over thousands of miles and their energetic needs vary along the migration route. Stopover sites located along the edges of large geographic features such as the Gulf of Mexico may be especially important, as these areas serve as either the first or last stops before an overwater crossing, and these areas are threatened by population growth and sea level rise. We examined the foraging behavior (attack rate and movement rate) and used automated radio-telemetry data to examine activity rates between two primary habitats (coastal scrub and mangrove) at a stopover site located on the southern coast of the Gulf of Mexico during autumn migration for four focal songbird species; Swainson's Thrush (Catharus ustulatus), Red-eyed Vireo (Vireo olivaceus), Gray Catbird (Dumetella carolinensis), and Prothonotary Warbler (Protonotaria citrea). We also examine the relationship between activity rates and stopover duration and departure direction. Our results indicate that each species has distinct habitat preferences; Gray Catbirds and Swainson's Thrushes spend more time, are more active, and displayed lower movement rates in coastal scrub, and also demonstrated a stronger positive relationship between activity rate and stopover. Prothonotary Warbler and Red-eyed Vireo demonstrated a weaker relationship between activity and stop over. Red-eyed Vireos also displayed lower movement rates in mangrove, although activity was not different between habitat types. Our data show that migratory songbirds use coastal scrub and mangrove based on species-specific differences, and all coastal habitats near ecological barriers should be preserved for migratory songbirds.
Solomon, Lauren E., "Stopover Ecology of Neotropical Migratory Songbirds in the Northern Yucatan Peninsula, Mexico" (2016). Masters Theses. 2511.