BEHAVIOUR OF THE ALEUTIAN GREY‐CROWNED AND BROWN‐CAPPED ROSY FINCHES LEUCOSTICTE TEPHROCOTIS

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SummaryVisual and vocal displays of Brown‐capped Rosy Finches Leucosticte tephrocotis australis, observed in Rocky Mountain National Park, Colorado, and of Aleutian Grey‐crowned Rosy Finches L. t. griseonucha on Adak Island, Alaska, are compared and contrasted with general behaviour among the Fringillidae.Visual display behaviour of the two subspecies is very similar. Vocal displays, as shown by sonagrams, are by comparison divergent. Most of the sound energy in the flock call of griseonucha is concentrated in a single band of frequencies. The range of these frequencies is small, and the call is whistle‐like to the human ear. The flock call of australis, more like that of other finch species, consists of three major bands of frequencies. Based on this difference, it is hypothesized that the flock call of griseonucha may be specialized for penetration of high background noise, which characterizes the windy environment of the Aleutians. In ambient noise that extends across the frequency range of the flock calls, the narrow‐range flock call of griseonucha is relatively high in signal/noise ratio. Some divergence in vocal display may also result from social mimicry in the respective habitats. The flight call of australis is click‐like, and more like the flight call of the 8ympatric Violet‐green Swallow Tachycineta thallasinea than that of griseonucha or of descriptions of the flight call of other finches.The two races differ also in general breeding habits. The breeding season, from first sexual chasing to fledging of young, in griseonucha spans nearly seven months; the study population was sedentary. In australis, individuals migrate in summer to alpine breeding grounds, and the events of breeding occur within about two months. Males were observed to feed their mates during the nesting period, in both races. Male and female fed the young and removed excreta from the nest, with about equal frequency.Both australis and griseonucha have marked excesses of males in the mature populations, but both are monogamous. It is considered that the unbalanced sex ratio may have selective effects on the behaviour associated with reproductive activity.