Incubation behavior, embryonic heart rate, and developmental variation within and among altricial bird species
The incubation period of an egg is a critical stage that has multiple implications in subsequent life stages, therefore understanding the processes within the egg during the incubation period are important for a broader understanding of avian development and life history strategies. I examined embryonic heart rate (EHR) within 14 sympatrically breeding grassland and shrubland bird species in east-central Illinois from April to August of 2019 and 2020. Specifically, I aimed to investigate 1) the factors that impact EHR across species, 2) how parental incubation behaviors impact EHR, 3) rates of hatching failure across species, and 4) the factors that drive variation in hatching failure across species. EHR was positively related to both the age of the embryo, as well as egg temperature. Additionally, EHR increased as the breeding season progressed and was negatively associated with clutch size. The EHR across the incubation period were similar across focal species, however, the two cavity nesting species, Eastern Bluebirds (Sialis sialis) and Tree Swallows (Tachycineta bicolor), exhibited lower EHR than the other species, while Dickcissels (Spiza americana) exhibited higher EHR than other species. Eastern Bluebirds also displayed greater nest temperature variation and a lower percent of time on the nest. Hatching failure was more common in cavity nesting species and nests with greater clutch sizes. A majority of embryonic death occurred before or shortly after the onset of incubation. The high rates of embryonic death in large clutches and early stages suggest the rates of mortality may be due to the delayed onset of incubation or the inability of females to adequately incubate large clutches. Overall, differences in life-history strategies across species may lead to differences in EHR and hatching failure.
avian embryonic heart rate, bird parental care, incubation behavior, hatching failure, embryonic mortality, embryonic development
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign