Territory Size in Mixed-grass Prairie Songbirds

I estimated breeding territory size in mixed-grass prairie songbirds, and explored how it varied among bird species, time-of-season, and year. The study was conducted at Bowdoin National Wildlife Refuge in north-central Montana during 2007-2009. Across all species, months and years, mean breeding territory size was estimated at 0.43 ha (SE = 0.03, n = 129). Estimates were nearly identical across study species: Sprague's Pipits (Anthus spragueii), Grasshopper (Ammodramus savannarum), and Baird's (A. bairdii) sparrows. There was no significant variation in territory size across months, suggesting little to no dependence on nest phase. In contrast, I found significant variation in territory size among years (P = 0.034), that did not interact meaningfully with species (R-2 = 0.02, P = 0.603). This suggests that factors that vary annually appear to be affecting all bird species in a similar manner, which could be related to differences in vegetation structure and/or site quality (perhaps as a function of weather) or less likely, variation in population density.