William D. Wishart

EFFECTS OF AGE, SEX, DISEASE, AND DENSITY ON SURVIVAL OF BIGHORN SHEEP

Longitudinal studies of survival are valuable because age-specific survival affects population dynamics and the evolution of several life history traits. We used capture–mark–recapture models to assess the relationship between survival and sex, age, population, year of study, disease, winter weather, and population density in two populations of bighorn sheep (Ovis canadensis) in Alberta, Canada. The Ram Mountain population, monitored for 20 yr, more than doubled in density; the Sheep River population, monitored for 13 yr, experienced a pneumonia epizootic. Yearling survival varied among years and was lower than that of older sheep of the same sex, except for yearling males at Ram Mountain. Yearling females at Ram Mountain were the only sex-age class exhibiting density dependence in survival. Senescence was evident for both sexes in both populations. Female survival from age 2 to age 7 was very high in both populations, but males aged 2 and 3 yr enjoyed better survival than males aged 4–6 yr. Our data support the suggestion that where hunters remove many males older than 5 yr of age, the natural mortality of males increases at 3–5 yr, possibly because young males suffer a mortality cost of participating in rutting activity. The decline in survival for sheep older than 7 yr was greater for males than for females. Survival was lower for males than for females, both among prime-aged sheep (0.896 vs. 0.939 at Sheep River; 0.837 vs. 0.945 at Ram Mountain) and among older sheep (0.777 vs. 0.859 at Sheep River; 0.624 vs. 0.850 at Ram Mountain), but not among yearlings. Survival of sheep aged 2–7 yr was not significantly different between the two populations. Winter weather did not affect survival. Survival of sheep 2 yr of age and older did not vary significantly between years, except at Sheep River where survival of prime-aged sheep of both sexes was lower in the year of the pneumonia epizootic. Studies of survival of mountain sheep based upon skull collections may have overestimated survival of young rams. Our results underline the need for accurate information on age-specific survival.

Life History Consequences of Variation in Age of Primiparity in Bighorn Ewes

We investigated the life history consequences of age at primiparity in two marked populations of bighorn sheep (Ovis canadensis), studied for 19 and 12 yr. Some ewes first lambed at 2 yr of age, others at 3 or 4 yr. Lambs of 2-yr-old ewes were smaller and less viable than lambs of older ewes. Lactation at 2 yr did not affect survival to 3 yr, but in one population it was associated with reduced survival from 3 to 4 yr. Two yr olds that weaned lambs gained less mass during summer than other 2 yr olds. Overwinter mass loss from 2 to 3 yr was correlated with autumn body mass, and was lower for parous than for nonporous ewes. Reproductive success at 3 yr was independent of reproductive status at 2 yr. At 4 yr, ewes that lactated as 2 yr olds were smaller than ewes that had not lactated as 2 yr olds. In one population, negative effects of early maturation upon mass gain and subsequent reproductive success became evident at high density, and very few 2 yr olds lambed when population density was high. The lifetime reproductive success of early- maturing ewes was not lower than that of late-maturing ewes. To account for individual variation in initial reproductive potential, we controlled body mass as a yearling, a variable that affected reproductive success. Mass as a yearling, however, did not interact with age of primiparity to affect survival, growth, or reproductive success. Uncertainties about re- source availability and possible effects of genotype and body fat may explain why many ewes postponed their first reproduction despite apparently low life history costs of early maturation.

Harvesting bighorn ewes: consequences for population size and trophy ram production

We wanted to test whether ewe hunting would cause a decline in population size or in trophy ram production, and whether a reduction in ewe density would increase the size of ram horns. Thus, we examined the consequences of a bighorn sheep (Ovis canadensis) ewe hunting season through an experimental manipulation of an isolated population in Alberta, 1972-91. The number of ewes remained stable during 9 years despite yearly removals of 12-24% of the total ewe population. The removals did not affect (P>0.5) ewe mortality due to other causes, lamb production by adult ewes, or lamb survival

Effects of population density on horn development in bighorn rams

Trophy hunting is a management goal for many populations of ungulates and has important implications for conservation because of the economic value of trophy males. To determine whether population density affected horn growth of males, a marked population of bighorn sheep (Ovis canadensis) in Alberta, Canada, was studied for 27 years. For the first 9 years, population density was kept stable by removing adult females; afterwards, the numbers of ewes and yearlings tripled before beginning to decline. Horns were measured during repeated captures of marked rams. As the number of adult ewes and yearlings increased, ram horns were shorter and thinner because of decreased horn growth before 4 years of age. Some compensatory horn growth may have occurred at 5 years of age. The effects of population density on horn growth ceased when rams left the nursery groups to join all-male groups. Doubling of male numbers had no detectable effect on net annual horn growth of males ≥4 years old. Spring precipitation had no apparent effect on horn growth of males 3-4 years old, and had a minor positive effect on horn base circumference for rams 5-6 years old. The proportion of rams 6-7 years old that attained 4/5 of a curl decreased from 61-73% at low density to 33-35% at high density. When bighorn sheep populations increase to a density where intraspecific competition in nursery herds affects horn development of young rams, limited ewe harvests may prevent a decrease in size of horns of mature males.

Age Determination of Pheasants by Measurement of Proximal Primaries

A technique is described for separating adult from juvenile ring-necked pheasants (Phasianus colchicus), from measurements of the shaft diameter and total length of the first primary. The pheasant is one of a few Galliformes to molt all ten primaries during their postjuvenal molt (Petrides 1942:323). Most other gallinaceous game birds retain the outer two juvenal primaries and these feathers are commonly used for separating adults from juveniles. The complete molt of primaries in pheasants has apparently caused investigators to abandon the wing and look elsewhere for age separation between adults and immatures. Ideally, an age criterion should be quantitative and have no overlap between ageclasses. Stokes (1957), and Gates (1966) have shown, for example, that age determination from spurs of male pheasants does not meet either of these standards. Not only do spur lengths overlap, but there is overlap in qualitative characteristics as well. The bursal-depth technique (Linduska 1943) has remained the most reliable aging method for pheasants described to date. However, one of the main weaknesses of both the spur and the bursa as aging criteria is that their reliability becomes questionable after midwinter, that is, the length of the spur of This content downloaded from 157.55.39.210 on Sat, 30 Jul 2016 05:19:26 UTC All use subject to http://about.jstor.org/terms AGING PHEASANTS BY PROXIMAL PRIMARY MEASUREMENT * Wishart 715 Table 1. Comparison of post-juvenal primary 1 measurements of male and female ring-necked pheasants sampled at 16-18 weeks in October, and 48-50 weeks in May. DIAMETER OF PRIMARY 1 (MM) LENGTH OF PRIMARY 1 (MM) AGE-SEX CLASS N x SE Range N x SE Range Male (16-18 wks) 109 3.06 ? 0.01 2.76-3.38 108 163.5 ? 0.42 153-175 Male (48-50 wks) 76 3.05 +0.01 2.84-3.29 62 164.1 + 0.56 155-176 Female (16-18 wks) 100 2.79 0.01 2.60-3.03 100 148.7 ? 0.50 138-161 Female (48-50 wks) 100 2.77 + 0.01 2.40-3.00 82 149.0 ? 0.52 139-160 juveniles progressively continues to increase and the depth of the bursa of juveniles continues to decrease as the bird becomes older. The purpose of this study was to investigate the use of proximal primaries as age criteria in pheasants. The proximal primaries were selected because, as post-juvenal feathers, they are completely grown at about 10-11 weeks and are retained for approximately 1 year (Westerskov 1957:2627). Although the proximal post-juvenal primaries are adultiform, their growth is completed by a bird that is approximately one-half adult size (Westerskov 1957:29). Thus, the proximal post-juvenal primaries are unlikely to be as large as the proximal postnuptial primaries which are grown by adults about the same time of year. I am indebted to J. Pelchat, Alberta Fish and Wildlife Branch, for the care and maintenance of the experimental birds. I wish to thank R. Finegan, B. C. Fish and Wildlife Branch, B. Murray and E. Ewaschuk, University of Alberta, and Janis Hall, formerly of the Alberta Fish and Wildlife Branch, for their assistance in taking several thousand wing measurements. I am grateful to F. C. Zwickel, University of Alberta, for his critical reading of the manuscript.