Emigration Behavior of Clark's Nutcracker

Abstract

-Eruptive movements of the Clark's Nutcracker (Nucifraga columbiana) were observed during the late summer and fall of 1977, 1978 and 1979 in northern Utah and adjacent states. Over 2,000 emigrating nutcrackers were seen during these periods. Eruptions began in mid to late August, about the time nutcrackers began foraging on developing conifer cones, and continued until early October. Nearly all nutcrackers traveled in small, loose flocks (i = 10.1 individuals). During 1977-1978, most emigrating nutcrackers appeared to winter in pihnon-juniper woodlands of Utah and adjacent states and no nutcrackers were reported outside their normal breeding range. A northward movement of nutcrackers, presumably the same population observed emigrating southward in fall 1977, was noted in summer 1978. Evidence for breeding of nutcrackers on their wintering areas is presented. A compartmental model summarizes current knowledge on the temporal and spatial aspects of nutcracker emigration. Clark's Nutcracker (Nucifraga columbiana) inhabits montane coniferous forests of western North America from Arizona and New Mexico to central British Columbia (A.O.U. Check-list 1957). At irregular intervals, nutcrackers leave their usual breeding range to winter in lowland deserts, plains and coastal areas. Davis and Williams (1957, 1964) concluded that these eruptions are caused by poor conifer seed crops, an important food for Clark's Nutcrackers during the fall, winter and breeding seasons (Mewaldt 1956, Vander Wall and Balda 1977, Giuntoli and Mewaldt 1978, Tomback 1978). Population densities of nutcrackers at the time of cone crop failure may influence the magnitude of eruptions (Davis and Williams 1957, 1964). Populations of the Eurasian Nutcracker (N. caryocatactes) also erupt during years of low conifer seed production (Formosof 1933). In this paper we describe eruptions of the Clark's Nutcracker through the mountains of northern Utah and adjacent states. Specifically we: 1) describe timing of fall and summer eruptive movements; 2) contrast behavior and flock structure of emigrant versus resident nutcrackers; 3) describe probable wintering areas of the emigrants; 4) discuss conditions which may influence the decision of emigrating nutcrackers to settle in an area for the winter; and 5) present evidence for breeding of emigratory nutcrackers on their wintering areas during the spring. Based on data presented here and elsewhere (primarily Davis and Williams 1957, 1964) we construct a compartmental model relating temporal and spatial patterns of Clark's Nutcracker eruptions. The nutcrackers seen moving through n rthern Utah did not originate there but from areas to the north. Resident nutcracker populations in northern Utah did not participate in the eruption. Throughout this paper, nutcrackers observed moving through Utah and adjacent states and these birds on their wintering areas are referred to as emigrants (i.e., we describe nutcracker movements with respect to their area of origin). Nutcrackers that did not participate in an eruption are referred to as residents. STUDY AREA AND METHODS Emigrating flocks of Clark's Nutcrackers were studied at three places in northern Utah and one in eastern Nevada (Fig. 1). Most of the information on behavior and flock structure was taken at a site (elev. 2,560 m) in the Wellsville Mountains (elev. 2,850 m) in northern Utah (Fig. 1, number 1). The Wellsville Mountains are a steep, narrow range with a north-south axis. Observations were made in late summer and fall of 1977 (6, 14 and 19 August and 27 August through 25 October), 1978 (27 August, 3 and 4 September and 6 September through 20 October) and 1979 (6 September through 10 October and 12 through 17 October) from approximately 11:00 to 16:30. Additional observations at elevations of 2,560 and 2,000 m in the nearby Bear River (Fig. 1, number 2) and Promontory (Fig. 1, number 3) mountains, respectively, were made irregularly from 28 August to 15 October 1977. In 1979, emigrating flocks of nutcrackers were observed from 19 to 24 September and 4 to 11 October in the Goshute Mountains, Nevada (elev. 2,750 m; Fig. 1, number 9). In the sum-