Role of landscape composition and geographical location on breeding philopatry in grassland passerines : a stable isotope approach

Grassland bird populations in North America are in steady decline.Despite declining faster and more consistently than any other group of birds, grassland songbird populations are relatively understudied and little is known about factors driving breeding-site philopatry and dispersal.Landscape and habitat composition may influence fidelity of grassland songbirds to a breeding area.As predicted by the theory of the Ideal Free Distribution, high-quality sites are likely to have a higher percentage of return breeders than low-quality sites because higher quality sites should have more or better-quality resources birds need for improved fitness.Using stable hydrogen isotope (D) analysis, I approximated minimum fidelity rates of two grassland songbirds to two landscape (grass-vs crop-dominated landscapes) and two habitat (native grass vs planted grass) types.I hypothesized that grassland songbirds would return more readily to higher quality sites.For Sprague's Pipit (Anthus spragueii), a habitat specialist, this would mean returning more readily to native grass habitat in grass dominated landscapes.I expected no difference in return rate of Savannah Sparrow (Passerculus sandwichensis), a habitat generalist, to either habitat or landscape.However, I found that the proportion of non-returning breeders was not influenced by landscape or habitat for either species.Furthermore, I examined attributes (distance from capture point to nearest crop and to the nearest road, as well as the percentage of native grass, planted grass, water and woody vegetation within landscape and territory buffers around the capture point) of the landscape and territory of each individual to determine if specific landscape or territory characteristics influenced their return rate to a breeding area.Neither species showed an affinity or aversion to any of the landscape or territory characteristics considered.At a larger scale, geographical position within the breeding range may influence dispersal rates of migratory songbirds.Given that environmental factors often change in a clinal manner, data, respectively.Many thanks to the staff of the Last Mountain Lake National Wildlife Area for their assistance and interest in

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