Temporal Patterns of Territorial Behavior and Circulating Testosterone in the Lapland Longspur and Other Arctic Passerines

Abstract

We studied territorial aggression in relation to circulating testosterone levels in free-living birds of four species in northern Alaska. The Lapland longspur, Calcarius lapponicus , is an abundant breeding passerine on the arctic tundra. Unlike many passerines at lower latitudes, male Lapland longspurs do not defend a “multiple-purpose territory” that serves to provide nest sites, food and shelter. Rather, after arrival on the breeding grounds, they perform aerial display flights over a loosely denned “nest area” for a very brief period of two days or so, showing tolerance of other males. This song display may be involved in courtship. During this phase, male longspurs show a brief and pronounced peak in circulating testosterone levels, and are not aggressive toward simulated territorial intrusions (STIs). Males then “guard” their sexually receptive mates for about ten days, during which they are highly aggressive toward STIs, but do not sing as much. During the next phase, incubation, the males become very tolerant of conspecific males. Their circulating testosterone levels decline to baseline levels, and they generally do not sing or display aggression in response to STIs. Three other passerines, the white-crowned sparrow, Zonotrichia leucophrys gambelii , American tree sparrow, Spizella arborea , and savannah sparrow, Passerculus sandwichensis , show patterns of territorial aggression typical of species studied at lower latitudes. Welldefined territories are defended for several weeks, during which there is a prolonged peak in plasma concentrations of testosterone. These three species continue to sing and display aggression even late in the season, unlike the longspurs. The peak of testosterone in the longspurs occurs simultaneously with the peak in song display, while in mid-latitude species it occurs with the peak in reproductive aggression. These data suggest that the interrelationship of testosterone and aggression in Lapland longspurs may be different from that of passerines with multiple-purpose territories, and may be related to the constraints of breeding in the open arctic tundra.