Territory, Breeding Density, and Fall Departure in Cassin's Finch
TERRITORY, BREEDING DENSITY, AND FALL DEPARTURE IN CASSIN'S FINCH FRED B. S^•rSON WHETHERterritory during the breeding seasonacts as a mechanism to regulate breeding density or total numbers within a population of birds has aroused much interest (Hinde 1956, Wynne-Edwards 1962, Lack 1966, Brown 1969, Klomp 1972, Von Haartman 1972, Watson 1973), but controversyremains. Kluyver (1970), after studying Great Tit (Parus major) populationson the Dutch Island of Vlieland in the North Sea, indicatedthat tit numbersare regulatedin early autumn after breed- ing. In the presentinvestigation, different populationsof Cassin'sFinch (Carpodacuscassinii) were studiedduring the breedingseason and early autumn of 3 years, to determinefactors influencing breeding density and population numbers. I selectedCassin's Finch to study becauselittle is known of its breed- ing biology or postbreedingbehavior. Published descriptionsof repro- ductive activities are few, most often by residentnaturalists or those engagedin faunistic surveys (Ridgway 1877, Henshaw 1879, Grinnell 1908, Taylor 1912, Dawson 1923, Bailey 1928, Grinnell and Miller 1944• Jones and Baylot 1969), presumablybecause accessibility to montane breeding populationsis limited. Fall studies are restricted to noting numbersseen or distributionallists (Orr 1968). The breedingrange for Cassin'sFinch extendsfrom southernBritish Columbia,Alberta, and Manitoba into northernArizona and Baja Cali- fornia (Bailey and NeJdtach 1965). These authors suggestedthat Cas- sin's Finch, like the crossbill(Loxia spp.), breed whereveran abundance of food exists within their range, with specificlocations changing from year to year. For breeding, Cassin'sFinch prefers a mixed forest habitat of the alpine meadow zone generally above 1500 m (Salt 1952). Most nests are located on ends of upper branchesin tall pines (Orr 1968), and pairs may nest in coloniesor singly (Lack 1968).
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