Adult Female Survival Rates Research Articles

Changes in landscape composition influence the decline of a threatened woodland caribou population

1. Large-scale habitat loss is frequently identified with loss of biodiversity, but examples of the direct effect of habitat alterations on changes in vital rates remain rare. Quantifying and understanding the relationship between habitat composition and changes in vital rates, however, is essential for the development of effective conservation strategies. 2. It has been suggested that the decline of woodland caribou Rangifer tarandus caribou populations in North America is precipitated by timber harvesting that creates landscapes of early seral forests. Such habitat changes have altered the predator-prey system resulting in asymmetric predation, where predators are maintained by alternative prey (i.e. apparent competition). However, a direct link between habitat condition and caribou population declines has not been documented. 3. We estimated survival probabilities for the threatened arboreal lichen-feeding ecotype of woodland caribou in British Columbia, Canada, at two different spatial scales. At the broader scale, observed variation in adult female survival rates among 10 distinct populations (range = 0.67-0.93) was best explained by variation in the amount of early seral stands within population ranges and population density. At the finer scale, home ranges of caribou killed by predators had lower proportions of old forest and more mid-aged forest as compared with multi-annual home ranges where caribou were alive. 4. These results are consistent with predictions from the apparent competition hypothesis and quantify direct fitness consequences for caribou following habitat alterations. We conclude that apparent competition can cause rapid population declines and even extinction where changes in species composition occur following large scale habitat change.

Toxicity of Spirodiclofen to the Predatory Mite, Amblyseius womersleyi (Acari: Phytoseiidae), and its Prey, Tetranychus urticae (Acari: Tetranychidae)

The relative toxicity of spirodiclofen to the predatory mite, Amblyseius womersleyi Schicha (Acari: Phytoseiidae), and its prey, Tetranychus urticae Koch (Acari: Tetranychidae), was evaluated in laboratory bioassays. Spirodiclofen was much less toxic to A. womersleyi than to T. urticae. Although the survival rate of adult females of A. womersleyi tended to decrease with increasing concentrations of spirodiclofen, 62–96% of the predators survived at concentrations of 22.5–180 ppm. Reproduction of adult female predators was only significantly affected at high concentrations (90 and 180 ppm). Spirodiclofen did not affect the hatch of A. womersleyi eggs at any concentration tested. Survival of immature predators was significantly decreased with increasing spirodiclofen concentration, however, 30–78% of immature predators reached adulthood at 22.5–45 ppm. Adult female predators survived on a diet of spider mites treated with spirodiclofen, and their fecundity was not significantly affected. Moreover, immature predators developed normally on prey treated with spirodiclofen. Spirodiclofen at selective sublethal concentrations (i.e., 22.5–45 ppm) could be of value in adjusting the prey/predator ratio in integrated management of T. urticae.

Does Life History Predict Risk-Taking Behavior of Wintering Dabbling Ducks?

AbstractLife-history theory predicts that longer-lived, less fecund species should take fewer risks when exposed to predation than shorter-lived, more fecund species. We tested this prediction for seven species of dabbling ducks (Anas) by measuring the approach behavior (behavior of ducks when approaching potential landing sites) of 1099 duck flocks during 37 hunting trials and 491 flocks during 13 trials conducted immediately after the 1999–2000 waterfowl hunting season in California, USA. We also experimentally manipulated the attractiveness of the study site by using two decoy treatments: (1) traditional, stationary decoys only, and (2) traditional decoys in conjunction with a mechanical spinning-wing decoy. Approach behavior of ducks was strongly correlated with their life history. Minimum approach distance was negatively correlated with reproductive output during each decoy treatment and trial type. Similarly, the proportion of flocks taking risk (approaching landing sites to within 45 m) was positively correlated with reproductive output. We found similar patterns of approach behavior in relation to other life-history parameters (i.e., adult female body mass and annual adult female survival rate). Thus, species characterized by a slower life-history strategy (e.g., Northern Pintail [A. acuta]) were more risk-averse than species with a faster life-history strategy (e.g., Cinnamon Teal [A. cyanoptera]). Furthermore, although we were able to reduce risk-averseness using the spinning-wing decoy, we were unable to override the influence of life history on risk-taking behavior. Alternative explanations did not account for the observed correlation between approach behavior and life-history parameters. These results suggest that life history influences the risk-taking behavior of dabbling ducks and provide an explanation for the differential vulnerability of waterfowl to harvest.

DOES LIFE HISTORY PREDICT RISK-TAKING BEHAVIOR OF WINTERING DABBLING DUCKS?

Life-history theory predicts that longer-lived, less fecund species should take fewer risks when exposed to predation than shorter-lived, more fecund species. We tested this prediction for seven species of dabbling ducks (Anas) by measuring the approach behavior (behavior of ducks when approaching potential landing sites) of 1099 duck flocks during 37 hunting trials and 491 flocks during 13 trials conducted immediately after the 1999–2000 waterfowl hunting season in California, USA. We also experimentally manipulated the attractiveness of the study site by using two decoy treatments: (1) traditional, stationary decoys only, and (2) traditional decoys in conjunction with a mechanical spinning-wing decoy. Approach behavior of ducks was strongly correlated with their life history. Minimum approach distance was negatively correlated with reproductive output during each decoy treatment and trial type. Similarly, the proportion of flocks taking risk (approaching landing sites to within 45 m) was positively correlated with reproductive output. We found similar patterns of approach behavior in relation to other life-history parameters (i.e., adult female body mass and annual adult female survival rate). Thus, species characterized by a slower life-history strategy (e.g., Northern Pintail [A. acuta]) were more risk-averse than species with a faster life-history strategy (e.g., Cinnamon Teal [A. cyanoptera]). Furthermore, although we were able to reduce risk-averseness using the spinning-wing decoy, we were unable to override the influence of life history on risk-taking behavior. Alternative explanations did not account for the observed correlation between approach behavior and life-history parameters. These results suggest that life history influences the risk-taking behavior of dabbling ducks and provide an explanation for the differential vulnerability of waterfowl to harvest.

SURVIVAL PROBABILITY ESTIMATES FOR LARGE JUVENILE AND ADULT GREEN TURTLES (CHELONIA MYDAS) EXPOSED TO AN ARTISANAL MARINE TURTLE FISHERY IN THE WESTERN CARIBBEAN

The largest remaining green turtle (Chelonia mydas) population in the Atlantic is potentially threatened by the resurgence of a commercial artisanal green turtle fishery in Nicaragua. Nicaragua is the site of the principal feeding ground for adults from the Tortuguero, Costa Rica, rookery. Little is known about the life history parameters of this population away from the nesting beach. To better understand the potential impact of harvesting in Nicaragua on the Tortuguero population, we estimated survival rates of adult females tagged on the nesting beach at Tortuguero, and a mixed group of large juveniles and adults tagged at turtle fishing sites in Nicaragua. Based on band recovery analysis, large juvenile and adult green turtles tagged at Nicaragua turtle fishing sites have a very low annual survival probability, 0.55. Adult females tagged on the nesting beach, which may forage at a broad range of Caribbean feeding grounds, had an annual survival probability of 0.82. These survival rate estimates are likely too low to sustain the population and have important implications for the future of the Tortuguero rookery.

Morphology and Population Characteristics of Vancouver Island Cougars, <em>Puma concolor vancouverensis</em>

Cougars are a management concern on Vancouver Island because they are a top predator and because there have been frequent attacks on humans on the island. However, little is known about Cougar ecology in the Pacific Northwest of North America. We studied Cougar morphology and population characteristics as part of a larger study in two areas on Vancouver Island. We derived a multivariate measure of body size to describe changes with age and sex. Body size was similar in the two study areas. Survival rates for adult females were higher than those reported elsewhere; however, hunters avoided shooting females in general, and radio-collared Cougars in particular. Litter size at first detection was lower than reported in many other studies and may be related to food availability.Includes erratum for a figure in this article.

Females Delay Dispersal and Breeding in a Solitary Gerbil, Meriones tamariscinus

We studied dispersal and breeding patterns in a solitary gerbil, Meriones tamariscinus, from 1995 to 1999 in Kalmykia, southern Russia. The females of this species delay breeding far beyond the age of maturation. We suggest that delayed breeding in young females is associated with delayed emigration from the natal site. Most young female M. tamariscinus showed strong natal philopatry that resulted in female kin clustering. Proximity to adult females suppressed their maturation and restricted breeding opportunities. Breeding rate of young females correlated negatively with the survival rate of adult females. Therefore, dispersal and breeding patterns in this solitary species appear similar to those in social (group living) species of gerbils. Results are discussed in terms of ecological, demographic, and life-history traits of this species that set constraints on dispersal and breeding in young females.

Influence of adult and egg predation on reproductive success of Epirrita autumnata (Lepidoptera: Geometridae)

We studied the effects of predation and oviposition activity on reproductive success of a late‐season moth, Epirrita autumnata by exposing adult females and eggs to predation in their natural habitat in two successive years. Daily survival rates of adult females ranged from 0.4 to 0.8, average being 0.7. Most predation occurred during nights and was caused by harvestmen and other invertebrate predators. Avian predation did not have an effect on adult survival rates, most likely because of the lateness of E. autumnata flight season. Eggs were also preyed upon by invertebrate predators, although a notable proportion of egg mortality was attributable to causes other than predation. Daily survival rates of eggs were more than 0.99. Using modeling based on empirical data on eclosion of female adults, their oviposition behavior and survival rates of adults and eggs, the daily survival rates were translated into population level consequences. Adult predation was estimated to decrease reproductive success of non‐outbreaking E. autumnata by 60–85 percent and egg mortality by 20–40 percent. Predation on adult lepidopterans is a mortality factor potentially as relevant as predation in any other life history stage and thus, should not be ignored in studies of population regulation.

Population Dynamics of the Wandering Albatross Diomedea Exulans at Marion Island: Longline Fishing and Environmental Influences

The subantarctic Prince Edward Islands (Marion and Prince Edward) support the largest breeding population of the Vulnerable wandering albatross Diomedea exulans. The number of birds breeding at Marion Island has fluctuated over the past three decades apparently as a result of both real changes in the size of the population and changes in the proportion of the population that attempts to breed in a given year. Changes in several demographic parameters that appear to be influenced by both environmental and anthropogenic effects are described. From 1994–2001, the proportion of first-time breeders in the population was positively correlated with the maximum ENSO (Niño 3) index, whereas from 1984–2000 the annual survival rates of breeding adults were negatively correlated with Japanese pelagic longline fishing effort in the southern Indian Ocean. Adult survival rates were significantly correlated with those on neighbouring Possession Island, Crozet Islands, but differed from those at South Georgia, suggesting common factors operating at an ocean-basin scale. The average survival rate of adult females was lower than that of males. Males who lost partners took 40% longer than females to find a new mate, suggesting a male-biased population. Survival rates of juvenile males and females did not differ. The age distribution of first-time breeders shifted progressively towards younger birds during the 1990s. Higher than expected survival rates of breeding adults during the late 1990s may be linked to large amounts of supplementary food being made available by the initiation of a longline fishery for Patagonian toothfish Dissostichus eleginoides close to the islands at this time. Overall, breeding success was better than recorded at other localities, indicating that breeding conditions at Marion Island were comparatively favourable. The early implementation of both international and national conservation initiatives to reduce the impact of longline fishing on this species and improve its conservation status is encouraged.

Modelling the influence of demographic parameters on group structure in social species with dispersal asymmetry and group fission

Female philopatry characterizes many mammal populations subdivided into social groups. Fission of these social groups is a relatively discrete event in the life of groups or of individuals, leading to the distribution of females among several newly formed groups. Fission is an important event because it can be a way for females to disperse. Group fissions have rarely been observed and their modalities generally remain poorly known, the best-documented species being primates. Most group fissions occur along lines of maternal relatedness, but the death of a matriarch may disrupt the cohesion within a matriline, inducing separation of sisters, accompanied by their descendants, when a group splits. Our model shows that the numbers and sizes of matrilines within groups depend on the precise demographic parameters and age structure of a population and not only on its rate of increase. For comparable population-growth periods, high survival rates of adult females induce an increase in the sizes of matrilines, whereas high survival rates of immature individuals induce an increase in the numbers of matrilines. Following fission, groups of a given size included, in the first case, only a few large matrilines, whereas in the second case, they consisted mainly of many small matrilines. The present study constitutes a preliminary stage, before modelling consequences of demographic structure of groups or populations on their genetic structure.

Demography of barren-ground grizzly bears

Between May 1995 and June 1999, we equipped 81 barren-ground grizzly bears (Ursus arctos) with satellite radio collars within a study area of 235 000 km2, centred 400 km northeast of Yellowknife, Northwest Territories, Canada. We used data from radiotelemetry to estimate survival rates, reproductive parameters, and the finite rate of increase of the population (λ). The annual survival rate of adult females was estimated at 0.979 (95% confidence intervals (CI) = 0.955–0.998), while the survival rate of adult males was 0.986 (95% CI = 0.942–1.0). The cub survival rate was 0.737 (95% CI = 0.600–0.844) and the yearling survival rate was 0.683 (95% CI = 0.514–0.821). Cub litter size averaged 2.23 (SE = 0.13, n = 35), while yearling litter size decreased to a mean of 1.86 (SE = 0.12, n = 35). The mean litter size of females with 2-year-olds was 1.85 (SE = 0.15, n = 20). The mean birth interval was 2.8 years (SE = 0.3 years, n = 17). The mean reproductive interval, which is calculated by excluding the loss of whole litters from the sample, was 3.9 years (SE = 0.4 years, n = 9). Mean litter size divided by mean birth interval yielded an annual natality rate of 0.81 cubs per adult female per year. The mean age at first parturition was 8.1 years (SE = 0.5 years, n = 10). We believe the population to be currently stable or slightly increasing (λ = 1.033, 95% CI = 1.008–1.064).

Nesting area fidelity and survival of female Common Goldeneyes Bucephala clangula: are they density‐dependent?

The breeding histories of 218 female Common Goldeneyes Bucephala clangula were recorded between 1971 and 2000 in a study area in Schleswig‐Holstein, northern Germany. Females were first recorded breeding at a median age of 2 years usually in their area of hatching (philopatry). One hundred and two of 140 females (73%) re‐nested only in one of the 13 nesting areas (clusters of nestboxes) for all their known life of up to 13 breeding seasons. The remaining 38 individuals moved between different nesting areas at least once between breeding attempts. The two oldest females were still breeding at a minimum age of 15 years (i.e. 13 years between first and last recorded breeding attempt). Temporal variations in annual survival rates of adult females could best be explained by a model with annual survival rate varying independently and randomly about a mean of 0.830 (se = ±0.023) with an estimated sd of ±0.092 (95% CI = 0.064, 0.138). No trend in the annual survival rate was detected over the study period of 30 years, although the presence of a moderate trend could not be ruled out. The absence of any discernible trend in survival at a time when the population size increased substantially indicates little, if any, density‐dependence in survival of female Goldeneyes during this study.

Proximate Factors Limiting Population Growth of White-Tailed Deer in Nova Scotia

White-tailed deer (Odocoileus virginianus) densities in Nova Scotia, Canada, declined during the late 1980s and early 1990s. We estimated population change, survival, and relative importance of mortality factors for deer in 2 geographic areas of Nova Scotia from February 1994 to January 1999. Pellet-group surveys indicated that deer densities in both study areas increased slowly (λ was approx. 1.07 and 1.05 in the Queens County and Cape Breton study areas, respectively) during the study. Annual survival rates of adult deer did not differ among years or between the study areas. Annual survival rates for adult females averaged 93.9 ± 4.3% (SE) and 80.4 ± 3.1% within and outside of Kejimkujik National Park, respectively, where harvest did not occur. Annual survival rates of adult males and fawns outside of the park, where hunting occurred, were 50.7 ± 7.6% and 36.9 ± 7.4%, respectively. No marked adult males or fawns died within the park during the study (winter only for fawns). Annually, hunting (34.2 ± 8.2% and 8.2 ± 2.4% for adult males and females, respectively) and predation (7.2 ± 5.3% and 7.5 ± 2.3% for adult males and females, respectively) were the largest mortality factors for adult deer. Coyote (Canis latrans) predation (27.5 ± 8.7% during Dec-May only) was most influential for fawns. Monte Carlo simulations involving a model of adult survival and fawn recruitment supported the results of the deer pellet-group inventories and suggested low but positive rates of increase for both populations. Although predation and the unregistered harvest of adult females probably slowed the growth of deer populations following the decline, the recent establishment of a zone-based antlerless harvest quota system should allow managers to regulate deer numbers by annually adjusting the number of antlerless permits in response to estimates of hunting and nonhunting losses.

Demographic processes in colonizing populations of isard (Rupicapra pyrenaica) and ibex (Capra ibex)

AbstractRates of increase, survival and reproduction were studied in two re‐introduced populations of mountain ungulates, the Pyrenean chamois (also named isard, Rupicapra pyrenaica) and the ibex (Capra ibex) in the French Alps. The populations were monitored from 1983 to 1998 (ibex) or 1984 to 1999 (isard) using capture, marking and resighting of individuals. Population rates of increase were estimated during the colonizing phase from: (1) a time series of estimates of population size; (2) projection matrices based on rates of survival and fecundity. Both populations had exponential rates of increase, with annual multiplication rates of 1.28 for isard and 1.30 for ibex. Age of first reproduction was 2 years in both species, with 77% of females breeding at this age in isard and 43% in ibex. From 3 years of age onwards, 90% of isard and 87% of ibex females bred each year. Survival rates of adult females, estimated using capture–recapture models, equalled 0.94 for isard and 0.98 for ibex, whatever the age and year. The projection matrix led to a slightly lower asymptotic multiplication rate than the time series of population size. Despite adult body size of the ibex being about twice that of the isard, no difference was detected in the intrinsic rate of increase between the two species. This supported the hypotheses of homogeneous life‐history traits among ungulates, varying little with body size.

Moose (Alces alces) survival in three populations in northern Norway

We used radio-collared individuals to examine the seasonal, annual, and regional variation in age-specific survival of moose (Alces alces) in three populations (Vega, Beiarn, and Troms) in northern Norway. In the two populations subject to a regular hunt, the annual mortality from hunting was higher, on average, than that from natural mortality for adult cows. In these study areas, the hunting mortality rate was higher for calves than for cows. For both age groups there was significant annual variation in hunting mortality, which was associated with differences in quota size among years. The survival rate of adult cows was high outside the hunting season (96%). There was seasonal variation in survival among calves, the highest significant mortality being found among neonates during summer in Vega and Troms and significantly higher mortality being found during winter in Beiarn. The natural mortality of calves differed significantly among regions during both summer and winter. The combined effects of density dependence, changes in age structure, and environmental stochasticity may explain this variation in calf-survival rate. In contrast, no significant seasonal or regional variation occurred in the survival rate of adult females.

Fragment size and the demography of an area‐sensitive songbird

Summary 1. Many songbird species are absent from small forest fragments. One possible explanation for this finding is that populations in small fragments decline to extinction because reproductive success is too low to compensate for adult mortality (λ < 1). I tested this hypothesis from 1995 to 1997 by measuring reproductive success, adult survival, and population viability for four banded populations of the Eastern yellow robin (Eopsaltria australis, White), an area‐sensitive songbird. The populations inhabited two small (55 ha, termed S1, S2) and two large (500–1000 ha, termed L1, L2) forest fragments set within an agricultural landscape. 2. Females produced more fledglings but a similar number of independent young per capita in the small compared to the large fragments. Local female survival did not vary with fragment size. 3. Population models were used to calculate the finite rate of increase (λ) from the number of young produced (female yearlings per female per year) and adult female survival rates. Combining data from all four populations, λ = 0·96, indicating that robins produced 4% fewer female young per year than were needed to compensate for adult losses. Combining data from the two small fragments, λ = 1·02, suggesting that populations in small fragments were viable on average. In contrast, λ = 0·85 for the two large fragments combined, indicating that, on average, 15% fewer young were produced than were needed to replace missing adults each year. Averaging across fragments within the same size class masked the variability in population dynamics that existed between the replicates. Considering each of the four fragments separately, there was one potential demographic source (S2, λ = 1·12; L2, λ = 1·23) and one demographic sink (S1, λ = 0·90; L1, λ = 0·46) within each of the fragment size categories. 4. Observed changes in population sizes were similar to those predicted by the population models. Combining all populations, recruitment replaced most but not all missing females, and the observed population size declined by 8% per year. In both the small and large fragments, observed recruitment was insufficient to replace missing females and population sizes declined 5% and 8% per year, respectively. Within each of the fragment size categories, there was one stable population (S2 and L2) and one population that declined in size (S1 and L1, respectively, declined by 14% and 20% per year). 5. Reproductive success, adult survival, and population viability did not vary with fragment size. To explain area‐sensitivity, I suggest that a threshold in fragment size exists below which populations are never viable, but above which populations may or may not be viable depending on factors unrelated to fragment size, such as nest predation rates.

Spatial explicit demography: The effects habitat patch isolation have on vole matrilines

Populations of many species are spatially structured in matrilines, and their dynamics may be determined by matriline specific demographic processes. We examined whether the isolation of habitat patches (i.e. interpatch distance) affected the demography of matrilines in 14 experimentally fragmented populations of the root vole. Matrilines inhabiting the most isolated patches decreased in size over the breeding season, while matrilines in less isolated patches increased. The survival rate of adult females was the main factor underlying the variation in growth rates among matrilines. Low survival when patches were isolated seemed to be due to long‐distance interpatch movements exposing females to increased predation rate.The differential success of matrilines in patchy populations with variable interpatch distances acted to decrease the matrilineal diversity at the population level. Furthermore, isolated patches may function as sinks. Thus spatially explicit landscape features may affect both population demography and genetics.

Extended parental care in marine amphipods: II. Maternal protection of juveniles from predation

Many terrestrial invertebrate parents effectively protect their offspring from predation. In this study, I examined whether marine amphipods that engage in extended parental care are able to provide protection from predation for their offspring. Two species, Leptocheirus pinguis and Casco bigelowi, host their juveniles in burrows while the epibenthic Dyopedos monacanthus cares for its offspring on mud whips. The size of amphipod dwellings was positively correlated with their body size, with large individuals of the burrow-dwelling L. pinguis and C. bigelowi inhabiting deeper burrows. The survival rates of adult females of L. pinguis and C. bigelowi exposed to sand shrimp ( Crangon septemspinosa) predators were very high, while those of D. monacanthus females were relatively low. Juveniles of L. pinguis (filter-feeder), C. bigelowi (deposit-feeder) and D. monacanthus (suspension-feeder) in presence and absence of their mothers were exposed to predators. In the filter-feeding species L. pinguis, the effects of predators on juvenile survival was significantly reduced by maternal protection. In the experiment with C. bigelowi, juvenile survival was significantly affected by predation but not by maternal protection. Many C. bigelowi juveniles that left the burrows of their mothers during the experiment were severely affected by predation, but smaller juveniles that remained in the maternal burrows survived in the predator treatments. Juvenile D. monacanthus were significantly affected by predation but not by maternal care. Juvenile D. monacanthus that remained on the maternal mud whip during the experiment survived exposure to predators, while those that had already built their own mud whips did not. Despite the experiments for C. bigelowi and D. monacanthus revealed parental protection only at a closer look, it is concluded that extended parental care in all three amphipod species is an effective mechanism to protect juveniles from predation. The results indicate that maternal dwellings are important structures where juveniles find protection. While protection from predation may be one of the most important benefits of extended parental care in these amphipods from shallow subtidal soft-bottoms, juveniles may also benefit in other ways as is suggested by reports on maternal food-provisioning and grooming.

Mule Deer Survival in Colorado, Idaho, and Montana

We examined survival rates of mule deer (Odocoileus hemionus) fawns (1 Jan-31 May) and adult (≥1 vr old) females (1 Jun-31 May) from Colorado, Idaho and Montana to assess the influence of survival on population dynamics over a broad geographic area. Survival rates were estimated from 1,875 radiocollared fawns and 1.536 radiocollared adult female-vears. We found significant year-to-year differences in overwinter survival rates of fawns among states (P < 0.001), while annual survival rates of adult females showed less variation across vears (P < 0.256). Sampling distributions of survival rates by age class were modeled with the beta-binomial distribution (BBD) and not found different among states (ad F: P = 0.118; fawns: P = 0,856), The mean overwinter survival rate for fawns was 0.444 (SE = 0.033), with SD = 0.217 (SE = 0.019). The mean annual survival rate for adult females was 0.853 (SE = 0.011), wiht SD = 0.034 (SE = 0.014). All 3 states exhibited differences in body size of fawns at the start of winter across years, and body size was a predictor of overwinter survival (P < 0.001). Fawn sex ratios in December at time of capture were not different from 50;50 (P = 0.729). However, a sex differential in overwinter survival of fawns was observed (P = 0.002), but beta-binomial models of survival distributions were not different between sexes (P = 0.458). Frequencies of 3 categories of proximal causes of fawn mortality predation, winter malnatrution other) differed among states (X 2 4 = 41.24, P < 0.001 ). A deterministic model with a mean winter survival rate of 0.444 for fawns and an annual rate of 0.853 for adult females predicted December fawn:doe ratios would have to be at least 66: similar processes regulate these populations hence results from specific study areas are generally more applicable than commonly thought.

Survival estimates for the northern spotted owl

An analysis of capture-recapture data is tailored to the biological characteristics of the female northern spotted owl (Strix occidentalis caurina) by conditioning female capture on capture of paired males. This procedure is relevant for animals such as the northern spotted owl where field studies indicate that capture of females generally is dependent on capture of their mates. Application of the method to data collected in Washington State suggests that survival rates for adult females have remained constant over the time span of our data, 1990-1997.