Dispersal, Overwinter Mortality, and Recruitment of Spruce Grouse
1979; Wiley; Volume: 43; Issue: 3 Linguagem: Inglês
10.2307/3808750
ISSN1937-2817
Autores Tópico(s)Rangeland and Wildlife Management
ResumoDispersal and autumn to spring mortality of juvenile spruce grouse (Canachites canadensis franklinii) were studied in southwest Alberta in 1970-73. Changes in breeding population size primarily resulted from changes in numbers of yearlings recruited. Dispersal in autumn did not change the size or sex ratio of the juvenile cohort. The reduction in total juveniles during autumn and winter averaged 12%. Survival over winter for all age and sex classes averaged 88%. Ninety percent of the loss of juveniles during autumn through spring was attributed to emigration. Among spring emigrants, known survival into summer was at least 64% and survival for 1 year was at least 54%. Dispersal in spring was more variable than in autumn and was important for changing numbers of potential recruits. Density did not appear to affect the magnitude of dispersal. J. WILDL. MANAGE. 43(3):717-727 Among Tetraonidae, losses of young during autumn and winter presumably are most responsible for changes in size of the breeding population (Boag 1966; Bendell and Elliott 1967; Zwickel and Bendell 1967a; Rusch and Keith 1971; Bendell 1972a,b; Weeden and Theberge 1972). However, there has been some recent modification of that conclusion. Bendell et al. (1972) and Zwickel (1972) emphasized the importance of behavioral interaction in early spring to recruitment of new birds. With few exceptions (Watson 1965, Jenkins et al., 1967, Rusch and Keith 1971) little has been done to study losses of birds in autumn and winter and the effect of those losses on recruitment (Bendell 1972b). The objectives of my study were to monitor changes in numbers of juvenile spruce grouse caused by dispersal and mortality from autumn through spring, and to evaluate impact of the changes on recruitment into a breeding population. Franklin's spruce grouse were chosen for study because McCourt (1969) and McLachlin (1970) indicated that they could be captured and observed easily, and that turnover rates were low. Spruce grouse were suspected to be less migratory than some other tetraonids, thus facilitating year-round work at a single site. I express thanks to D. A. Boag and F. C. Zwickel, University of Alberta, for their interest and stimulation, for their many arguments about interpretations, and for their reviews of early drafts of the manuscript. I thank the following students for field assistance in summer: the late W. Etherington, A. Garbutt, M. Henderson, R. Salter, K. Smith, and D. Thompson. STUDY AREA AND METHODS The study area of 5.2 km2 at an elevation of 1,500-2,000 m was adjacent to Gorge Creek (50'39'N, 114'39'W), near the R. B. Miller Biological Station, 27 km west of Turner Valley, Alberta. About 70% of the area was dominated by lodgepole pine (Pinus contorta), 25-35 years 1 Financial support was provided by Postgraduate Scholarships from the National Research Council of Canada (1971-74), a Conservation Education Grant (1972-73) from the National Wildlife Federation, and the University of Alberta. D. A. Boag, University of Alberta, provided funds for equipment and assistants through a N.R.C. Operating Grant. The University of New Brunswick partially supported publication costs. 2 Present address: Departments of Forest Resources and Biology, University of New Brunswick, Fredericton E3B 5A3, Canada. J. Wildl. Manage. 43(3):1979 717 This content downloaded from 207.46.13.169 on Sun, 03 Jul 2016 06:07:40 UTC All use subject to http://about.jstor.org/terms 718 SPRUCE GROUSE IN ALBERTA *Keppie old and mostly 7-13 m tall. Small patches of mature white spruce (Picea glauca), quaking aspen (Populus tremuloides), and balsam fir (Abies balsamea) occurred on the area. Most understory tree growth was white spruce, with alder (Alnus crispa) and willow (Salix spp.) as common shrubs. Grouse occupied immediately contiguous forest on half of the perimeter of the study area. Grouse were located with pointing dogs and censused repeatedly by searching subsections of the study area on a rotation basis during a continuous 40month period between May 1970 and September 1973. Grouse were captured with an extendable snare pole (Zwickel and Bendell 1967b) and were marked with individual color combinations of leg bands. Sex and age of grouse over 40 days old were determined from plumage (Zwickel and Martinsen 1967, Ellison 1968). The classification for age was: juvenile, from hatch in year x to 1 April of x + 1; yearling, to 1 April of x + 2; adult, after 1 April of x + 2. April 1 was the dividing date because it approximated breakup of winter flocks and beginning of dispersal. The breeding population was the adult and yearling grouse on the study area between 15 May and 15 August. This interval excluded migrants. Courtship occurred before 15 May but nearly all breeding occurred after that date. Yearlings present by 15 May were considered recruited because they were present during primary breeding activity and likely were an important component in the social system even if they did not mate. Autumn was from 1 September to the start of winter. Winter started with permanent snow cover, beginning 10 November 1970, 17 December 1971, and 1 December 1972. Winter ended 31 March, approximately at the beginning of loss of snow cover. Spring refers to 1 April to 15 May. Dispersal is normally considered as movement from birth to 1st breeding site (Dice and Howard 1951, Haukioja 1971). In this study, movement to potential breeding sites occurred in autumn or spring; some juveniles moved at both times, others only once, and others not at all. For juveniles moving in both seasons the autumn move to a winter site was considered to be a part of their total dispersal movement because most habitat used in winter was potential breeding habitat. Juveniles that moved from brood range or winter range without leaving the study area are, herein, not termed dispersers. The dispersal process was measured numerically as the net of numbers of emigrants and immigrants. Most emigrants moved far enough that they had little or no contact with remaining residents during the breeding period. Therefore, emigration was distinct from local
Referência(s)