González Crespo, Jean Paul

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    Spatial ecology of the yellow-shouldered blackbird during the post-fledgling period and its implication on population growth
    (2023-12-05) González Crespo, Jean Paul; Puente Rolón, Alberto R.; College of Arts and Sciences - Sciences; Santos Flores, Carlos J.; López Ortiz, Ricardo; Department of Biology; Barriga Burgos, Alicia
    In this thesis I showcase the results of a two-year study, conducted in Pitahaya mangrove forest and “Bahía Sucia” in southwestern Puerto Rico, focusing on estimating survival of the Yellow-shouldered Blackbird during the post-fledging period during the 2019 and 2020 breeding seasons. In this study, a total of 51 fledglings were tagged with radio-transmitters. The wing chord (p=0.005) and tarsus (p=0.035) were longer in 2019 than in 2020, but no significant difference was found in mass (p=0.94). Size disparity within nests revealed older siblings larger and more developed than younger ones, with significant mass differences (p=0.01). Older siblings also displayed superior flight capabilities, with 81% reaching the edge of the mangrove forest when fledging, compared to only 18% of younger ones. Survival rates between the two years showed little variation, with six deaths occurring among the tagged fledglings, resulting in survival rates of 0.897 (2019) and 0.870 (2020) – a non-significant difference (p=0.80). Initial post-fledging behavior had fledglings perched low, begging for food. However, by day 20, their plumage resembled that of adults, but they could still be identified by their begging behavior. Parental feeding decreased after 30-40 days but continued up to 62 days post-fledging. Mean, home range size for the 2019 and 2020 groups, using the MCP method, was 65 ha and 265 ha, respectively, and using KDE was 228 ha and 391 ha. However, these differences were not statistically significant. The morphological traits of wing chord length, and tarsus length showed significant relationship with home range size, while weight did not. This study also included the use of a seasonal population matrix model to determine the influence of each life stage on population growth, adjusting for species-specific sex ratios and using clutch sizes from the two years. Using stage transition matrices, the analysis identified adult survival as a critical factor in the species' population growth. Emphasizing the reproductive value of adults due to their ability to survive, this study also highlighted the importance of clutch and nestling survival, implying vulnerability to both density-dependent and non-density-dependent factors. The results indicate that the YSBL population in southwestern Puerto Rico is currently declining at a rate of approximately 42% per year. Furthermore, the multiple factors identified underscore the need for adaptive conservation and suggest a comprehensive approach to understanding the reproductive patterns and survival determinants of the Yellow-shouldered Blackbird.