Flushing distances of ferruginous hawks nesting in rural and exurban New Mexico

As natural environments become increasingly modified by humans, land managers should devise plans to protect sensitive species from human activities that disturb these species. We explored behavioral responses of nesting ferruginous hawks (Buteo regalis) to an approaching human in areas where the level of human activity on the landscaped varied. Contrary to other reports, hawks were aggressive in nest defense and female hawks defended nests more aggressively than male hawks. Adult hawks decreased nest-defense intensity as nestling age increased but increased intensity with consecutive human visits to the nest. Flushing distance was considerably higher than that documented in other studies and was negatively related to degree of urbanization. We found that a distance of 650 m prevented 95% of nest-attending ferruginous hawks from flushing in response to human intruders; thus we recommend establishing a spatial buffer of this distance or greater to minimize adverse effects of human activities on hawks nesting in New Mexico. © 2011 The Wildlife Society.     

Correlates of survival in Swainson's hawks breeding in northern California

We used a 30-year study of breeding Swainson's hawks (Buteo swainsoni) in northern California to examine correlates of adult apparent survival using multistate models in Program MARK. Specifically, we examined age-related patterns in adult apparent survival and how adult survival was correlated with average annual nest productivity, annual reproductive output, western juniper (Juniperus occidentalis) density around nest sites, distance to agriculture, and amount of agriculture within a territory. Annual estimates of adult survival varied from 0.85 to 0.9 (SE = 0.02). There were no indications of senescence or other patterns of age-related changes in adult apparent survival. Adult survival was inversely correlated with average reproductive output, with individuals producing >2 offspring having decreased survival, reflecting a possible trade-off between reproduction and survival. Conversely, reproduction in any year was positively correlated with survival, providing evidence of individual quality influencing adult survival. The distance an individual had to travel to agriculture, where most individuals forage, was negatively related to survival. Primary productivity within the average Swainson's hawk territory was positively correlated with adult survival. Our results indicate that individuals may have higher survival and fitness in areas with high proportions of irrigated agriculture that provides high prey densities, particularly alfalfa. © 2011 The Wildlife Society.     

Light grazing of saltmarshes is a direct and indirect cause of nest failure in Common Redshank Tringa totanus

The Common Redshank Tringa totanus breeding population on British saltmarshes has declined by over 50% since 1985, with declines linked to changes in grazing management. Conservation initiatives have encouraged low‐intensity grazing of less than one cattle per hectare, but Redshank have continued to decline, even in regions where light grazing was predominant. This study quantified effects of grazing intensity on Redshank nest survival over six lightly grazed saltmarshes with livestock densities between 0 and 0.82 cattle per hectare, in the Ribble Estuary, northwest England. We assessed whether grazing resulted in nest mortality directly through cattle trampling and/or indirectly through grazer modification of habitat that accelerates predation risks. Cattle density was recorded both during the Redshank breeding season and for 1 year prior to the study, to account for both short‐term trampling effects and the longer term effects on vegetation. Results showed that risk of nest loss to trampling increased from 16% at 0.15 cattle per hectare to 98% at 0.82 cattle per hectare in the breeding season. The risk of a nest being predated increased from 28% with no grazing to 95% at 0.55 cattle per hectare based on all year grazing data. These results suggest that even light conservation grazing at less than one cattle per hectare can reduce Redshank nest survival rates to near zero. It may therefore be appropriate to reduce saltmarsh grazing intensities, or change the timing of saltmarsh grazing to reduce the number of livestock present during the Redshank breeding season.     

Factors Affecting Nest Survival of Greater Sage-Grouse in Northcentral Montana

Abstract: We studied greater sage-grouse (Centrocercus urophasianus) in northcentral Montana, USA, to examine the relationship between nest success and habitat conditions, environmental variables, and female sage-grouse characteristics. During 2001-2003, we radiomarked 243 female greater sage-grouse, monitored 287 nests, and measured 426 vegetation plots at 4 sites in a 3,200-km² landscape. Nest survival varied with year, grass canopy cover, daily precipitation with a 1-day lag effect, and nesting attempt. In all years, daily survival rate increased on the day of a rain event and decreased the next day. There was temporal variation in nest success both within and among years: success of early (first 28 d of nesting season) nests ranged from 0.238 (SE = 0.080) in 2001 to 0.316 (SE = 0.055) in 2003, whereas survival of late (last 28 d of nesting season) nests ranged from 0.276 (SE = 0.090) in 2001 to 0.418 (SE = 0.055) in 2003. Renests experienced higher survival than first nests. Grass cover was the only important model term that could be managed, but direction and magnitude of the grass effect varied. Site, shrub and forb canopy cover, and Robel pole reading were less useful predictors of nest success; however, temporal and spatial variation in these habitat covariates was low during our study. We note a marked difference between both values and interpretations of apparent nest success, which have been used almost exclusively in the past, and maximum-likelihood estimates used in our study. Annual apparent nest success (0.46) was, on average, 53% higher than maximum-likelihood estimates that incorporate individual, environmental, and habitat covariates. The difference between estimates was variable (range = +8% to +91%). Management of habitats for nesting sage-grouse should focus on increasing grass cover to increase survival of first nests and contribute to favorable conditions for renesting, which should be less likely if survival of first nests increases.     

Sources and Patterns of Wolverine Mortality in Western Montana

ABSTRACT We instrumented 36 wolverines (Gulo gulo) on 2 study areas in western Montana and one study area on the Idaho-Montana (USA) border: 14 (9 M, 5 F) on the Pioneer study area, 19 (11 M, 8 F) on the Glacier study area, and 3 (2 M, 1 F) on the Clearwater study area. During 2002–2005, harvest from licensed trapping accounted for 9 (6 M, 3 F) of 14 mortalities, including individuals from all 3 study areas. Based on Akaike's Information Criterion adjusted for small sample sizes (AIC_c) rankings of 8 a priori models, a trapping model and a trapping-by-sex interaction model were equally supported (ΔAIC_c < 2) in explaining wolverine survival. Estimated annual survival was 0.80 when we did not consider harvest, whereas additive mortality from harvest reduced annual survival to 0.57. Glacier National Park in the Glacier study area provided some refuge as evidenced by an annual survival rate of 0.77 compared to 0.51 for the Pioneer Mountain study area. We incorporated these survival rates into a simple Lefkovitch stage-based model to examine rates of population change. The finite rate of population change (Λ) for the Glacier study area was 1.1, indicating a stable to slightly increasing population, whereas Λ for the Pioneer study area was 0.7, indicating a 30% annual population decrease during our study. Changes in Λ for both study areas were most sensitive to adult survival. In 2004, we used a Lincoln Index to estimate that 12.8 ± 2.9 (95% CI) wolverines resided in the 4 mountain ranges comprising the Pioneer study area, suggesting that small, island ranges in western Montana supported few individuals. Our results suggest that if wolverines are harvested, they should be managed within individual mountain ranges or small groupings of mountain ranges to limit mortality to within biologically defined limits in recognition of the increased vulnerabilities owing to low fecundity and low population numbers in small mountain ranges. We found that refugia, such as Glacier National Park, were important by reducing trap mortality and providing immigrants to the surrounding population, but even large parks were inadequate to provide complete protection to wolverines from trapping as they ranged outside park borders.     

Demographic Parameters of Rural and Urban Adult Resident Canada Geese in Georgia

ABSTRACT In many urban metropolitan areas, resident Canada goose (Branta canadensis) populations have grown to nuisance levels in spite of increasing harvest opportunity. To document differences in demographic parameters between urban and rural geese, I estimated probabilities of survival, recapture, recovery, and fidelity for adult resident Canada geese between 2001 and 2006 using banding, live recapture, and dead recovery data from 2 distinct banding locations in Georgia, USA. Adult survival rates were higher for urban geese (0.958, SE = 0.020) than for rural geese (0.682, SE = 0.049). Using estimated recovery probabilities of 0.505 (SE = 0.107) for urban and 0.463 (SE = 0.045) for rural geese, along with current estimates of crippling loss and reporting rate, the estimated mean harvest rate for urban geese was 0.029 (SE = 0.006) and for rural geese was 0.202 (SE = 0.020). Fidelity rates were similar between urban (0.730, SE = 0.033) and rural geese (0.713, SE = 0.069). This information suggests that urban segments of the Canada goose population have substantially higher survival than rural geese and are harvested at a very low rate, and that liberalizing hunting regulations may have little impact on Georgia's urban goose population. Wildlife managers may need to consider options other than sport hunting to control nuisance goose populations in urban areas.     

Demography of the Pacific walrus (Odobenus rosmarus divergens) in a changing Arctic

The Pacific walrus (Odobenus rosmarus divergens) is a candidate to be listed as an endangered species under United States law, in part, because of climate change‐related concerns. While the population was known to be declining in the 1980s and 1990s, its recent status has not been determined. We developed Bayesian models of walrus population dynamics to assess the population by synthesizing information on population sizes, age structures, reproductive rates, and harvests for 1974–2015. Candidate models allowed for temporal variation in some or all vital rates, as well as density dependence or density independence in reproduction and calf survival. All selected models indicated that the population underwent a multidecade decline, which began moderating in the 1990s, and that annual reproductive rate and natural calf survival rates rose over time in a density‐dependent manner. However, selected models were equivocal regarding whether the natural juvenile survival rate was constant or decreasing over time. Depending on whether juvenile survival decreased after 1998, the population growth rate either increased during 1999–2015 or stabilized at a lesser level of decline than seen in the 1980s. The probability that the population was still declining in 2015 ranged from 45% to 87%.     

Demography of the Pacific walrus (Odobenus rosmarus divergens): 1974–2006

Global climate change may fundamentally alter population dynamics of many species for which baseline population parameter estimates are imprecise or lacking. Historically, the Pacific walrus is thought to have been limited by harvest, but it may become limited by global warming‐induced reductions in sea ice. Loss of sea ice, on which walruses rest between foraging bouts, may reduce access to food, thus lowering vital rates. Rigorous walrus survival rate estimates do not exist, and other population parameter estimates are out of date or have well‐documented bias and imprecision. To provide useful population parameter estimates we developed a Bayesian, hidden process demographic model of walrus population dynamics from 1974 through 2006 that combined annual age‐specific harvest estimates with five population size estimates, six standing age structure estimates, and two reproductive rate estimates. Median density independent natural survival was high for juveniles (0.97) and adults (0.99), and annual density dependent vital rates rose from 0.06 to 0.11 for reproduction, 0.31 to 0.59 for survival of neonatal calves, and 0.39 to 0.85 for survival of older calves, concomitant with a population decline. This integrated population model provides a baseline for estimating changing population dynamics resulting from changing harvests or sea ice.     

Factors affecting the abundance of introduced hedgehogs (Erinaceus europaeus) to the Hebridean island of South Uist in the absence of natural predators and implications for nesting birds

Introduced hedgehogs Erinaceus europaeus are a known threat to ground-nesting birds on many islands. Spring hedgehog density and sex ratio were measured over a 5-year period at four plots on the 315 km² Hebridean island of South Uist. The mean instantaneous density on the sandy-soiled machair plots (31.8 hedgehogs km⁻², se 2.95) was over twice that on the peaty-soiled blackland plots (15.4 hedgehogs km⁻², se 3.46), a difference reflecting the amount of preferred foraging habitat (mainly pasture). Plot population densities fluctuated approximately in unison. Year-to-year density changes were strongly correlated with temperature in the preceding winter and previous year's spring/summer, indicating that warmer conditions promote both survival and breeding success. The mean spring sex ratio of sub-adults (animals born in the previous calendar year) was not significantly different from 1M:1F. However, the 1.8M:1F ratio observed for adults was significantly male biased, probably a result of female mortality associated with rearing young. The study estimates that in an average year the South Uist hedgehog population numbers c . 2750 (95% confidence limit±800) adults and sub-adults and these produce around 3000 young. Compared with the native range, hedgehog densities on South Uist are shown to be unusually high, probably because their natural predators are absent. High hedgehog densities have led directly to high rates of egg predation of ground-nesting shorebirds and subsequent declines in bird populations. The results suggest that over the past 20 years egg losses have become more severe and control of hedgehogs more difficult because climate warming has resulted in generally more favourable conditions for hedgehogs on the islands.     

Survival and Cause-Specific Mortality of Male Mule Deer Under Different Hunting Regulations in the Bridger Mountains,Montana

Abstract: We selected 2 adjacent populations of mule deer (Odocoileus hemionus hemionus) in the Bridger Mountains, Montana, USA, to measure effects on survival rates and causes of mortality of 2 hunting regulations designed to enhance representation of mature males. We compared male survival between the West Slope and South 16 Mile populations considering both hunting and nonhunting sources of mortality with respect to age (fawn, yearling, and mature), month (Jun-May), and year (1990-1995). Harvest rates of mature males were greater than for yearlings, demonstrating hunter preferences. We found no differences in yearling monthly survival rates between October and November or between areas or years. In contrast, we found survival of mature males differed between October and November and across years and study areas. During these months, survival rates of mature males averaged 0.602 on the West Slope under the 2-point regulation and 0.762 on South 16 Mile under the outfitted hunt. Monthly survival during summer also differed by age class, but not area, with estimates of 0.963 for yearling males, and corresponding mature male survival estimates of 0.991, demonstrating greater yearling summer mortality. Winter survival rates of yearlings and matures were similar for both areas with a monthly estimate of 0.986. We found differences in spring monthly survival estimates for the 2 areas, mainly for matures. Yearling male monthly survival estimates were 0.959 and 0.958 for the 2 areas, whereas corresponding mature male estimates during spring were 0.991 and 0.936 on the West Slope and South 16 Mile, respectively. Fawn survival rates varied from 0.101 to 0.770 among years and between areas overwinter. Cumulative effects of nonhunting mortality among all age classes reduced the effectiveness of 2 hunting regulations designed to enhance survival of males to age classes ≥4 years associated with maximum antler development despite accomplishing reductions in harvest rates. Low and variable fawn survival and relatively high nonhunting-related losses of yearling and mature males might be typical of many populations in the Northern Rocky Mountains. Deer managers should avoid populations coexisting with a diversity of large predators in environments with strong year effects when considering opportunities for implementing harvest regulations to improve representation of mature males.     

Separating Components of Variation in Survival of Mule Deer in Colorado

ABSTRACT Survival is an important parameter for understanding population dynamics of mule deer (Odocoileus hemionus) and other large herbivores. To understand long-term dynamics it is important to separate sampling and biological process variation in survival. Moreover, knowledge of correlations in survival across space and between young and adults can provide more informed predictions of survival in unsampled areas. We estimated survival of fawn, yearling, and adult mule deer from 4 spatially separated regions of Colorado, USA, from 1997 to 2008. We also estimated process variance in survival across time for each age and site using Markov chain Monte Carlo (MCMC) methods. Finally, we estimated correlations in survival among sites and ages with MCMC methods. Average winter fawn survival was 0.721 (SD = 0.024) for the 4 regions. Average winter adult female survival was 0.935 (SD = 0.007). Annual adult female survival ranged from 0.803 (SD = 0.017) to 0.900 (SD = 0.028) for the 4 regions, excluding hunting mortality. The correlation between fawn and adult female survival was high, 0.563 (SD = 0.253). Correlations in winter fawn survival were higher between populations at the same latitude than they were for populations to the north and south. We used survival estimates from our analysis to inform prior distributions for a Bayesian population dynamics model from one population in Colorado and compared that model to one with noninformative prior distributions. Population models including informative prior distributions based on our results performed better than those noninformative prior distributions on survival, providing more biologically defensible results when data were sparse. Knowledge of process distributions of survival can help wildlife managers better predict future population status and understand the likely range of survival rates.     

The population ecology of Rattus exulans on Tiritiri Matangi Island,and a model of comparative population dynamics in New Zealand

Abstract

On Tiritiri, a small predator-free island in northern New Zealand, kiore (Rattus exulans) were live and snap trapped in grassland and forest. In both habitats, kiore abundance peaked in late summer/autumn. The increase followed a 3 month breeding season during which females produced two to three litters, each averaging 7 young. During the population decline in autumn and winter, animals lost weight. Few bred in the breeding season of their birth and none lived to breed in a second breeding season, so the population consisted of distinct age cohorts. These patterns may relate to a highly seasonal food supply.

Kiore elsewhere in New Zealand show seasonal breeding, but the length of breeding, sexual maturation, and litter size vary. Other studies of kiore in the Pacific show less marked seasonal fluctuations, longer breeding seasons, and smaller litters. We propose a model to explain the variation in rodent demography in New Zealand. The model is based on the seasonal availability of food, along with the modifying influences of predation and dispersal.