Date of Award
Michael T. Murphy
Towhees -- Nests -- Oregon -- Portland, Towhees -- Behavior -- Oregon -- Portland, Habitat selection -- Oregon -- Portland
Nest site choice of birds has the potential to affect predation rates on nests and reproductive success for many bird species, and is thus tied closely to fitness. Vegetation at a particular site influences concealment (and predation rate as a result). Research has shown that birds of various species base nest site choice on variables like nest height, and especially vegetation cover within the microhabitat around a site. I studied nest site choice in ground-nesting birds, which tend to experience high predation rates near the nest site, and therefore might be expected to be particular choosy about vegetation near the nest. I used Spotted Towhees (Pipilo maculatus) nesting in Lesser Park in Portland, OR, as a model species for ground-nesting birds. I compared Spotted Towhees nest sites (n = 15) to both randomly-chosen sites within 10 m of the nests (n = 15; random territory sites) and other randomly-chosen locations throughout the park (n = 25; random park locations) to test whether vegetation structure and floristic composition differed. I measured (1) vegetation height and density near the nest, (2) size and spacing of trees around nests, and (3) floristic composition of vegetation near nests. I found that nest sites and both categories of random sites had dense and equal amounts of vegetation near ground level (0-20 cm above ground), but that nest sites had more vegetation between 21-40 cm and 61-100 cm above ground than random locations. However, there was no evidence that the structure of the tree community or species composition differed between nest sites and random locations. Towhees thus appear to prefer to place nests in locations with greater vertical cover directly over the nest.
Allen, Jazzmine, "Nesting Microhabitat Use by a Ground-nesting Songbird: Strict Preferences or Random Choice?" (2016). University Honors Theses. Paper 348.