Mean Annual Survival Rate Research Articles

Dynamics of a Black‐capped Chickadee Population, 1958‐1983

The dynamics of a wintering population of Black—capped Chickadees (Parus atricapillus) were studied from 1958—1983 using capture—recapture methods. The Jolly—Seber model was used to obtain annual estimates of population size, survival rate, and recruitment. The average estimated population size over this period was °160 birds. The average estimated number of new birds entering the population each year and alive at the time of sampling was °57. The arithmetic mean annual survival rate estimate was °0.59. We tested hypothesis about possible relationships between these population parameters and (1) the natural introduction of Tufted Titmice (Parus bicolor) to the area, (2) the clear—cutting of portions of nearby red pine (Pinus resinosa) plantations, and (3) natural variations in winter temperatures. The chickadee population exhibited a substantial short—term decline following titmouse establishment, produced by decreases in both survival rate and number of new recruits. Survival rate decline somewhat after the initiation of the pine clear—cutting, but population size was very similar before and after clear—cutting. Weighted least squares analyses provided no evidence of a relationship between survival rate and either of two winter temperature variables.

Survival of Coyotes in Southern Texas

Survival patterns of coyotes (Canis latrans) in southern Texas were studied from 1974 to 1982. Three estimates of annual survival rates of adult (?1.5-year-old) coyotes ranged from 0.68 to 0.70. A mean annual survival rate of 0.42 for juveniles from 0.5 to 1.5 years of age was estimated by the product-limit method. Juvenile survival was lower (P < 0.01) than adults during the cool season (Nov-Feb). Fifty-seven percent of 35 mortalities of radio-collared coyotes were attributed to human-related factors (shooting, trapping, road fatalities). A greater proportion of juvenile females egressed from marking sites than juvenile males or either sex of adults. Comparison of autumn and spring population age ratios implicated an age bias in sampling. J. WILDL. MANAGE. 49(2):301-307 Management strategies to alleviate depredation by coyotes on livestock or game animals must be developed from knowledge of population processes in different environments. Knudsen (1976), Davison (1980), and Tzilkowski (1980) provided data on survival rates and mortality factors in coyote populations affected by intensive human exploitation. Additional information on coyote survival is available from Knowlton (1972), Nellis and Keith (1976), and Andrews and Boggess (1978). Coyote abundance has been continuously high in southern Texas since estimates were begun in 1965 (Knowlton 1972, Bean 1981). Human exploitation of coyotes has been light in the region (Knowlton 1972) because control efforts for livestock protection were limited and sport hunting and trapping were sporadic. The objective of our study was to quantify survival rates and patterns and to determine mortality causes in this lightly exploited, high-density coyote population. We thank W. M. Stephensen, B. G. Wagner, Jr., and C. D. Mitchell for capturing coyotes. K. R. Quackenbush and K. L. Brown assisted with monitoring instrumented coyotes. W. E. Dusenberry provided assistance with data analysis. J. B. Finley, Jr., R. Killam, and G. S. Walker, Sr., generously cooperated by providing access to their private lands for this study. We thank F. F. Knowlton for advice and administrative support during the study. Constructive reviews of the manuscript were provided by F. F. Knowlton, L. C. Stoddart, A. W. Todd, and W. M. Tzilkowski.

Estimated survival rates for immature red drum in northwest Gulf of Mexico bays

A mean annual survival rate of 15 ± 2% (S.E.) was estimated for tagged red drum ( Sciaenops ocellatus) for the period November 1975–April 1979 in bays of the northwest Gulf of Mexico. Annual survival estimates were calculated as the product of four seasonal estimates. Seasonal survival estimates were based on tags recovered from recreationally and commercially harvested red drum. Seasonal red drum survival rates were lower for a 3-month summer period (36 ± 8% May–July) than for any other quarter (81 ± 9%) during the year. Survival rates were similar for two different size-groups (190–400 mm and 401–950 mm total length). Annual survival rates for red drum were as low or lower than any other exploited fish population for which survival rates have been published. The annual fishing mortality was estimated to be 46.5%.

Population Dynamics of Central Canadian Arctic Island Polar Bears

The range, abundance, and population dynamics of a hunted population of polar bears (Ursus maritimus) in the central Canadian Arctic Islands is described. Range was determined by tag returns and abundance by mark-recapture analysis. Population dynamics were based on family-group observations and life-table analysis using age samples obtained from teeth of live and killed bears. Based on 528 captures, including 60 recaptures, the abundance estimate was 1,100 animals with a mean annual survival rate of 0.87 and an overall annual natality rate of 0.47 cubs/reproductive age female/year. The population inhabits an area of approximately 45,000 km2 and exists in four semidiscrete subgroups between which exchange occurs.

The responses of a perch, Perca fluviatilis L., population to eutrophication and associated changes in fish fauna in a small lake

A number of parameters were measured in a population of perch whose numbers had declined steeply in a habitat subjected to increasing eutrophication, and these measurements were compared with those taken before the population decline. Contrary to expectation, no adaptive responses were identified. The growth rate of perch up to the age of III had only declined slightly, and there was a marked preponderance of young fish. Relative growth rate was consistent despite the population decline. No dominant year class was apparent. Mean instantaneous mortality rate and annual survival rate were calculated, and the length‐weight relationship was analysed. Feeding strategy had not altered since an earlier study. A decline was seen in the percentage of perch maturing at early age. Ripeness coefficients and fecundity estimates were calculated. A previously documented spawning migration was confirmed. The absence of the expected adaptive changes is discussed.

Effects of Elevated Temperature on Growth and Survival of Smallmouth Bass

Abstract The long-term effects (November 1977-October 1978) of elevated temperature on smallmouth bass, Micropterus dolomieui (age 0+ at stocking) were evaluated in outdoor channels located on the Tennessee River in Alabama, the southern limit of the native range of this species. Temperature treatments, with three channels per treatment, were at the ambient regime of the Tennessee River and 3, 6, and 9 C above ambient. Actual temperatures ranged from 1 to 30 C in the ambient channels and from 10 to 38 C in the +9 C channels. Under extreme summer conditions there was a 10% (by volume) refuge zone of 35 C water in the +9 C channels. Mean annual survival rates ranged from 84% in the +3 C regime to 92% in the +6 C regime; survival was 87% in both the ambient and +9 C treatments. Substantial growth occurred throughout the range 20 to 32 C. After 322 days, net biomasses of smallmouth bass in the four thermal regimes were not significantly different (range, 85–105 kg/hectare). Reproduction at age I occurred in a...

The Little Penguin Eudyptula Minor in Victoria, I: Mortality of Adults

The Little Penguin Eudyptula minor has been studied at Phillip Island, Vic., for nine seasons. The mean annual survival rate of breeding adults is estimated at 85.8 per cent, giving a mortality rate of 14.2 per cent per annum and a life expectancy of 6.5 years. Estimates for males and for females do not differ significantly. Birds that moved from the study area after breeding once have not been taken into account. Places, times and causes of mortality are given, where known.

MORTALITY AND KILL AMONGST BRITISH‐RINGED TEAL ANAS CRECCA.

Summary. 11,500 Teal were ringed in England and Wales between 1945 and June 1955. Most were caught in traps at Abberton Reservoir, Essex, or in duck decoys in Pembrokeshire and Northamptonshire. Cage traps seem to select older birds, rather than those in their first year of life, and males rather than females. Duck decoys show no sex bias, and no clear selectivity by age in late autumn and winter, when most British ringing has been done The mean annual survival rate of male Teal ringed in Britain 1949–1955 is 0±507±0·019 and that of females 0·430±0·021. Survival in the year following the first September of life may be rather less Teal of both sexes ringed in Pembrokeshire in 1934–1938 had an annual survival‐rate of 0·357±0·020, compared with 0·511±0·040 for birds ringed there in 1945–1948 and 0·350±0·029 for those ringed there in 1949–1953. In the later years of the 1939–1945 War, from 1941 onwards, the survival rate rose to 0·606±0·043 Reported causes of death of ringed Teal suggest that nearly all deaths are due to man, particularly in the months September to March. These reports exaggerate the proportion due to man, and the magnitude of winter losses, because losses due to man are nearly ten times as likely to be reported as those from other causes. The true proportion of losses attributable to man is probably about three‐fifths for males and one‐half for females. Losses from September to March account for about two‐thirds of the annual total for males and rather more than a half of the female casualties Losses in the summer are inversely proportional to those in the preceding winter: an unusually heavy winter kill is offset by a reduction in summer casualties, which include many “natural deaths”.