Water as a Habitat Cue for Breeding Swamp and Song Sparrows

Russell Greenberg
1988 The Condor  
Habitat use by Song (Melospiza melodia) and Swamp (M georgiana) sparrows was studied along 1.2 km of contact between the species in northwestern Pennsylvania. The two species had only narrowly overlapping territories (4 to 5%). Several lines of evidence suggest that the opposite response of territorial sparrows to the presence of surface water accounts for this spatial segregation. The presence or absence of water was a nearly perfect predictor of which species was defending a particular area
more » ... a particular area (95% correct), whereas a stepwise discriminant function based on 10 vegetative variables categorized the territories by species with only 74% accuracy. An area drained of water by the destruction of a beaver dam changed from containing five Swamp Sparrow territories to supporting five partial Song Sparrow territories; local densities of the two species were otherwise similar. During record rainfall and flooding in June of the second year of the study, male Swamp Sparrows were opportunistically defending newly developed flooded areas. Aggression between the species was not common and males did not respond to playbacks of heterospecific songs. These observations suggest that major changes in habitat distribution can occur through a change in response to a single habitat cue. The later arriving Swamp Sparrows are smaller and socially subordinate to Song Sparrows. Song Sparrows settle on dry territories leaving the wetlands to the Swamp Sparrows.
doi:10.2307/1368570 fatcat:oh6ch3fw6venronczpxctrsreu