Annual return rates of breeding grassland songbirds

Abstract

We used reobservation of color-banded birds to index annual breeding site fidelity of four species of songbirds that nest in the northern mixed-grass prairie of northcentral Montana (1996-2005). Territorial males of Sprague's Pipits (Anthus spragueii), and Savannah (Passerculus sandwichensis). Grasshopper (Ammodramus savannarum), and Baird's (A. bairdii) sparrows were located on five permanent study sites (1998-2004) and lured into mist-nets using tape broadcasts of conspecific songs and calls. The proportion reobserved was 5.3% (n = 247) across all banded adult males. Grasshopper Sparrows had the highest proportion of returns (8.9%), followed by Savannah Sparrows (5.4%), Baird's Sparrows (5.1%), and Sprague's Pipits (2.1%). Three nestling Savannah Sparrows were reobserved in subsequent years (n = 193), while no nestlings of the other species were reobserved (n = 401). Our return rates were low for all adults in comparison with typical reports of return rates for songbird species of woodland and shrubland habitats. Migratory nomadism may explain this phenomenon, where grassland migrants are opportunistic in site selection, rather than faithfully returning to potentially uninhabitable former breeding sites.