Howard M. Wight

Population Status of River Otter in Western Oregon

Population status of the river otter (Lutra canadensis) in western Oregon was evaluated by using structural population modeling. Survival and recruitment rates for the female segment of the population were estimated from the age structure of a sample of 113 female otters obtained from trappers during the 1970-71 and 1971-72 trapping seasons. Age was determined from cementum annuli in canine teeth. Annual survival rates were estimated to be 68, 46, and 73 percent for age-classes 0, 1, and 2-11, respectively. Recruitment was 1.14 female pups per adult female at the beginning of trapping season. Comparison of estimated survival and recruitment rates, by the modeling approach, revealed that the population was stationary. J. WILDL. MANAGE. 41(4):692-699 The reported harvest of river otters by fur trappers in Oregon declined 39 percent from the 1966-67 to the 1969-70 trapping seasons (Oregon State Game Commission 1967, 1968, 1969, 1970), indicating a possible decline in otter numbers. The reduced harvest may not have reflected population change because factors other than density may have influenced significantly the size of the otter catch. Preliminary investigation of the relation between fur prices and number of otters harvested in Oregon showed a positive correlation. Also, trappers who were interviewed stated that adverse weather conditions during the trapping seasons (primarily flooding and ice) reduced trapping effort and success. This paper reports a study we began in fall of 1970 to evaluate the status of the otter population in western Oregon, using a method other than the index based on harvest. A method for estimating population trends by evaluating the balance between population recruitment and survival through the use of a structural population model (Henny et al. 1970) was chosen for evaluating the status of the otter population examined in this study. This method appeared well suited to this population for which no census methods existed and available indices were not reliable, but for which a sample of harvested animals was readily available. MATERIALS AND METHODS Carcasses of 113 female otters harvested by trappers in Oregon during the 1970-71 a d 1971-72 trapping seasons (15 Novemb r-15 February) provided material for study. All otters in the sample were harvested in the western half of the state (Fig. 1). Determination of Age Layering in the cementum of an upper canine tooth was used to determine age of otters. Root portions of canines were decalcified in either buffered formic acid (Luna 1960) or 5 percent nitric acid, sectioned with a cryostat, stained in Papanicolaou Hemotoxylin Stain Solution (Fisher Scientific Company), and examined under a microscope (Tabor 1974). Thin, darkstained bands in the cementum could be 1 Study conducted under the auspices of the Oregon Cooperative Wildlife Research Unit: Oregon Department of Fish and Wildlife, Oregon State University, U.S. Fish and Wildlife Service and Wildlife Management Institute cooperating. Oregon State University Agricultural Experiment Station Technical Paper No. 4210. 2 Deceased 7 July 1975. 692 J. Wildl. Manage. 41(4):1977 This content downloaded from 207.46.13.33 on Sun, 20 Nov 2016 04:21:46 UTC All use subject to http://about.jstor.org/terms OREGON RIVER OTTER * Tabor and Wight 693

Weather Influences on the Onset of Breeding in Missouri Cottontails

The purpose of this paper is to report the effect on breeding in Missouri cottontails of a period of abnormally high snowfall and prolonged cold in February and March of 1960. In most years, central Missouri cottontails (Sylvilagus floridanus) begin breeding about the end of February. Schwartzs (1942) data for 1939 and 1940 showed first conception dates about March 1, and our own data for 1958 and 1959 show a median first conception date of February 26. The uniformity of the onset of breeding in these 4 years suggests a photoperiod effect governing the onset of breeding. Lyman (1943) demonstrated that altering the duration of illumination may modify greatly both the sexual and molting cycle in the varying hare. Bissonette (1938) and Bisson-

Annual production of a cottontail population

Adult females in a cottontail (Sylvilagus floridanus) population produced seven or eight litters during the 1961 breeding season. A synchrony of the conception dates was maintained throughout the breeding season. Data about ovulation rate, prenatal mortality, and litter size for each litter are presented. The first litter was smallest, averaging about three young, and the remaining litters ranged between five and six young. The last four litters may be slightly smaller than the second and third litters of the season. The total annual production of young by an adult female would be approximately 35. The purpose of this paper is to present information about the number of litters per year and litter size in a cottontail population. The number of litters produced annually by a female cottontail has been estimated variously from two (Allen 1938) to six (Schwartz 1942). The latter author concluded that in Missouri the average number of litters per female was 3.8. Figures for average litter size have also been given by various workers. Schwartz (1942) showed that litters were smallest at the beginning of the breeding season and largest during May and June. Lord (1961) also noted seasonal variation in litter size. Barkalow (1962) and Lord (1960) have reported that smaller litter size is a characteristic of the cottontail in the southern portions of its range. We wish to acknowledge the assistance provided by Faye Grogan and Leroy Heman in making collections of material at the James A. Reed Memorial Wildlife Area. Joan Clifford aided in preparation of laboratory materials. METHODS During 1961, rabbits were collected by shooting from wild populations on the Missouri Conservation Commissions James A. Reed Memorial Wildlife Area. This is a 1,800-acre management area in Jackson County near Kansas City, Missouri. It has a very productive soil and is intensively managed for upland game. During the late winter of 1960 this population suffered heavy mortality, and the onset of the reproductive season was delayed until late March (Wight and Conaway 1961). The population at the beginning of the breeding season in 1961 was still low. An initial collection of 15 female cottontails was made on March 17, 1961. All of these animals were lactating and had conceived again in a postpartum estrus. At the time of collection, 13 were in unimplanted stages and 2 in early implanted stages of their postpartum pregnancy. A second collection of 17 females was made on April 3 to obtain a sample in late gestation of the second pregnancy of the season. Fifteen of the 17 were between 20 days gestation and term. Periodic collections were made throughout the remainder of the year, as follows: (1) May 2, 17 pregnant females of which 1 This study is part of a cooperative project between the Department of Zoology, University of Missouri, and the Missouri Conservation Commission, supported in part by funds under Pittman-Robertson Project, Missouri 13-R-15. 2 Present address: Fish and Wildlife Service, Patuxent Wildlife Research Center, Laurel, Maryland.

Mortality Estimates of an Adult Band-Tailed Pigeon Population in Orgeon

In the period 1952-65, 3,140 band-tailed pigeons (Columba fasciata) were banded at Nehalem, Oregon, during each May and June when the birds were in prebreeding flocks of adults. These banding efforts averaged 56 new captures per trap-day over the 14-year period. The average annual mortality rate based on 262 recoveries was 28.7 percent. When return data were used to calculate mortality, 687 records indicated a rate of 29.1 percent. Productivity of this population, assuming that the population has remained relatively stable in size, was estimated to be about one young per pair when a 40 percent immature mortality rate was assumed. The purpose of this paper is to present estimates of adult mortality rates and deductions on the probable productivity of a population of band-tailed pigeons banded at Nehalem, Oregon. The band-tailed pigeon is a migratory game bird of the western states and provinces of the United States, Canada, and Mexico. It is a species of low productivity. Various authors (Bent 1932, Neff 1947, Morse 1949, and Glover 1953) report one egg per clutch and only one brood per year as normal. However, MacGregor and Smith (1955) in a study in Monterey County, California, found evidence of multiple nesting. One marked pair fledged three broods in 1954. One egg per clutch was considered normal in all studies. For the purpose of this paper, a recovery is defined as a banded bird shot or found dead and reported. A direct recovery is a recovery that occurs in the year of banding or more specifically during the hunting season that immediately follows the banding period. A return is a recapture of a bird from our bandings that occurs at the trap site one or more years following the year of banding. We wish to acknowledge the editorial assistance and statistical advice of W. Scott Overton, Department of Statistics, Oregon State University.

Characteristics of Wintering Flocks of Mourning Doves in Missouri

The purpose of this paper is to report on the sex and age composition, flock size and stability of wintering flocks of mourning doves (Zenaidura macroura) in north-central Missouri. Also included are data about doves collected in winter that were banded on the study area during preceding summers, suggesting the presence of a nonmigratory segment of this dove population. Summer banding of doves was begun by personnel of the Missouri Conservation Commission at the Fountain Grove Wild-