Variation in northern bobwhite demography along two temporal scales

Quantification and understanding of demographic variation across intra- and inter-annual temporal scales can benefit from the development of theoretical models of evolution and applied conservation of species. We used long-term survey data for northern bobwhites (Colinus virginianus) collected at the northern and southern extent of its geographic range to develop matrix population models which would allow investigation of intra- and inter-annual patterns in bobwhite population dynamics. We first evaluated intra-annual patterns in the importance of a seasonal demographic rate to asymptotic population growth rate with prospective perturbation analysis (elasticity analysis). We then conducted retrospective analysis (life table response experiments) of inter-annual patterns in the contribution of observed changes in demography to the observed change in population growth rate. Survival in the earliest age class during the nonbreeding season had the greatest potential influence in both the northern and southern populations. Examination of inter-annual variation in demography indicated that variation in nonbreeding season survival in the earliest age class contributed the most to observed changes in population growth rate in the northern population. In contrast, changes in fertility in the earliest age class in the southern population had the greatest influence on changes in population growth rate. Prospective elasticity analyses highlight the similarities in bobwhite demography throughout different parts of its geographic range, while retrospective life table response experiments revealed important patterns in the temporal differences of bobwhite life history at the northern and southern extent of its geographic range.     

Reproductive success of wild Lesser Rheas (Pterocnemia -Rhea- pennata pennata) in north-western Patagonia, Argentina

We studied the reproductive success of a wild Lesser Rhea population (Pterocnemia -Rhea- pennata pennata) during two reproductive seasons (2004/2005 and 2005/2006) in north-western Patagonia, Argentina. The parameters recorded included population and nest density, clutch size, hatching success, chick survival (up to 3 months of age) and percentage of chicks that reached the juvenile stage after the winter. We also estimated the percentage of males that attempted to nest and of those that were successful (those producing at least one chick), daily nest mortality rates (DNMR) at different stages of the nesting cycle and the probability that an egg that has been recently laid will produce a chick. On average, both years pooled, the density of this population of Lesser Rheas was 1.55 ± 0.2 individuals/km² (SE), nest density was 0.17 ± 0.04 per km ² , clutch size was 20.8 ± 6.4 eggs, hatching success was 74.4% ± 11.3, Mayfield’s probability of an egg that will produce a chick was 0.64, chick survival was 65.4% ± 14.5 and percentage of chicks that reached the juvenile stage was 26.3%. Nearly a quarter of Lesser Rhea males in the population attempted to nest during a breeding season, and the DNMR was significantly higher during the laying stage (most nest failures were due to anthropogenic disturbances related to livestock raising activities). Nesting success, hatching success, and chick survival of Lesser Rheas were higher than those of their most closely related species, the Greater Rhea (Rhea americana), whereas the percentage of chicks that reached the juvenile stage was similar due to high winter mortalities of chicks. We suggest that the increase in reproductive effort is a strategy of this species to overcome environmental constraints.     

Effects of Landscape-Scale Environmental Variation on Greater Sage-Grouse Chick Survival

Effective long-term wildlife conservation planning for a species must be guided by information about population vital rates at multiple scales. Greater sage-grouse (Centrocercus urophasianus) populations declined substantially during the twentieth century, largely as a result of habitat loss and fragmentation. In addition to the importance of conserving large tracts of suitable habitat, successful conservation of this species will require detailed information about factors affecting vital rates at both the population and range-wide scales. Research has shown that sage-grouse population growth rates are particularly sensitive to hen and chick survival rates. While considerable information on hen survival exists, there is limited information about chick survival at the population level, and currently there are no published reports of factors affecting chick survival across large spatial and temporal scales. We analyzed greater sage-grouse chick survival rates from 2 geographically distinct populations across 9 years. The effects of 3 groups of related landscape-scale covariates (climate, drought, and phenology of vegetation greenness) were evaluated. Models with phenological change in greenness (NDVI) performed poorly, possibly due to highly variable production of forbs and grasses being masked by sagebrush canopy. The top drought model resulted in substantial improvement in model fit relative to the base model and indicated that chick survival was negatively associated with winter drought. Our overall top model included effects of chick age, hen age, minimum temperature in May, and precipitation in July. Our results provide important insights into the possible effects of climate variability on sage-grouse chick survival.     

Feeding Ecology of Ring-Necked Pheasant and Northern Bobwhite Chicks in Conservation Reserve Program Fields

ABSTRACT Gamebird chick survival is dependent on invertebrate availability, and the ability to access insect prey is an important characteristic defining brood habitat quality. Different mixes of warm-season grasses and forbs were established to improve the habitat quality of fields enrolled in the Conservation Reserve Program (CRP) for gamebirds in the Southern Plains. We analyzed the feeding ecology of human-imprinted, 4- to 10-day-old ring-necked pheasant (Phasianus colchicus) and northern bobwhite (Colinus virginianus) chicks in wheat fields and 4 types of conservation practices (CP) fields enrolled in CRP (CP10, improved CP10, CP2, and CP25) in western Kansas, USA, during June and July, 2004 and 2005. Foraging rates were greatest for bobwhite chicks in improved CP10 and CP25 fields and greatest for pheasant chicks in CP10 and CP25 fields. Vegetation characteristics such as bare ground cover appear to have a significant impact on insect selection, because the diet was more diverse for both species in fields with more bare ground. The CP25 fields provided the best combination of mobility and diet breadth for both species. Although herbicide-treated wheat fields had low feeding rates, we determined non-herbicide-treated fields (i.e., weedy wheat) provided easy mobility and feeding rates similar to CRP fields. We suggest that management of vegetation to benefit gamebirds does not affect species equally. Feeding rates of bobwhite chicks were sensitive to vegetation-influenced mobility. Management of CRP fields for both pheasant and bobwhite chicks can be reconciled by practices that permit more open space at ground level, such as light disking or burning, to permit easier movement for chicks.     

Estimating Duration of Short-Term Acute Effects of Capture Handling and Radiomarking

ABSTRACT Radiotelemetry is used extensively in zoographic studies of wildlife species, including northern bobwhite (Colinus virginianus). These studies assume that radiomarking does not affect survival of marked individuals. However, most researchers implicitly acknowledge that capture, handling, and radiomarking may have short-term deleterious effects on individuals and, therefore, include in analyses only animals that survive an adjustment period of arbitrary length (often 7 days) following capture and marking. Length of adjustment period is rarely empirically based and may potentially bias survival estimates. We outline an analytical approach to determine an appropriate adjustment period and illustrate this approach by examining effects of time-since-marking on survival of 410 northern bobwhite captured during winter from 1997 to 2001, in Mississippi, USA. We modeled daily survival rates using time-since-marking as a covariate in the nest-survival model of Program MARK. Although survival varied among and within years, we found no evidence to suggest that standard adjustment periods of 7–14 days were appropriate for our sample. If adjustment periods are used in radiotelemetry studies, those that are empirically based may be more appropriate than arbitrarily set periods.     

Demographic Sensitivity of Population Change in Northern Bobwhite

Abstract: The northern bobwhite (Colinus virginianus) is an economically important gamebird that is currently undergoing widespread population declines. Despite considerable research on the population ecology of bobwhites, there have been few attempts to model population dynamics of bobwhites to determine the contributions of different demographic parameters to variance of the finite rate of population change (Λ). We conducted a literature review and compiled 405 estimates of 9 demographic parameters from 49 field studies of bobwhites. To identify demographic parameters that might be important for management, we used life-stage simulation analyses (LSA) to examine sensitivity of Λ to simulated variation in 9 demographic parameters for female bobwhites. In a baseline LSA based on uniform distributions bounded by the range of estimates for each demographic parameter, bobwhite populations were predicted to decline (Λ = 0.56) and winter survival of adults made the greatest contribution to variance of Λ (r² = 0.453), followed by summer survival of adults (r² = 0.163), and survival of chicks (r² = 0.120). Population change was not sensitive to total clutch laid, nest survival, egg hatchability, or 3 parameters associated with the number of nesting attempts (r²<0.06). Our conclusions were robust to alternative simulation scenarios, and parameter rankings changed only if we adjusted the lower bounds of winter survival upwards. Bobwhite populations were not viable with survival rates reported from most field studies. Survival rates may be depressed below sustainable levels by environmental conditions or possibly by impacts of capture and telemetry methods. Overall, our simulation results indicate that management practices that improve seasonal survival rates will have the greatest potential benefit for recovery of declining populations of bobwhites.     

Combining Breeding Bird Survey and Christmas Bird Count Data to Evaluate Seasonal Components of Population Change in Northern Bobwhite

Abstract Annual surveys of wildlife populations provide information about annual rates of change in populations but provide no information about when such changes occur. However, by combining data from 2 annual surveys, conducted in different parts of the year, seasonal components of population change can be estimated. We describe a hierarchical model for simultaneous analysis of 2 continent-scale monitoring programs. The Christmas Bird Count is an early winter survey, whereas the North American Breeding Bird Survey is conducted in June. Combining information from these surveys permits estimation of seasonal population variance components and improves estimation of long-term population trends. The composite analysis also controls for survey-specific sampling effects. We applied the model to estimation of population change in northern bobwhites (Colinus virginianus). Over the interval 1969–2004, bobwhite populations declined, with trend estimate of −3.56% per year (95% CI = [−3.80%, −3.32%]) in the surveyed portion of their range. Our analysis of seasonal population variance components indicated that northern bobwhite populations changed more in the winter and spring portion of the year than in the summer and fall portion of the year. (JOURNAL OF WILDLIFE MANAGEMENT 72(1):44–51; 2008)     

Use of Implanted Radiotransmitters to Estimate Survival of Greater Sage-Grouse Chicks

ABSTRACT Reduced chick survival has been implicated in declines of greater sage-grouse (Centrocercus urophasianus) populations. Because monitoring survival of unmarked sage-grouse chicks is difficult, radiotelemetry may be an effective technique to estimate survival rates, identify causes of mortality, and collect ecological data. Previous studies have used subcutaneous implants to attach radiotransmitters to hatchlings of several species of birds with precocial young. Previous researchers who used subcutaneous implants in free-ranging populations removed chicks from the capture location and implanted transmitters at an alternate site. Because logistics precluded removing newly hatched greater sage-grouse chicks from the field, we evaluated a method for implanting transmitters at capture locations. We captured 288 chicks from 52 broods and monitored 286 radiomarked chicks daily for 28 days following capture during May and June 2001–2002. Two (>1%) chicks died during surgery and we did not radiomark them. At the end of the monitoring period, 26 chicks were alive and 212 were dead. Most (98%, 207/212) radiomarked chick mortality occurred < 21 days posthatch and predation (82%, 174/212) was the primary cause of death. Necropsies of 22 radiomarked chicks did not indicate inflammation or infection from implants, and they were not implicated in the death of any chicks. Fate of 48 chicks was unknown because of transmitter loss (n = 16), radio failure (n = 29), and brood mixing (n = 3). Overall, the 28-day chick survival rate was 0.220 (SE = 0.028). We found that mortalities related to the implant procedure and transmitter loss were similar to rates reported by previous researchers who removed chicks from capture sites and implanted transmitters at an alternate location. Subcutaneous implants may be a useful method for attaching transmitters to newly hatched sage-grouse chicks to estimate survival rates, identify causes of mortality, and collect ecological data.     

Quantifying density dependence in a bird population using human disturbance

Although density dependence has long been recognised as vital to population regulation, there have been relatively few studies demonstrating it spatially in wildlife populations, often due to the confounding effects of variation in habitat quality. We report on a study of woodlarks Lullula arborea, a species of European conservation concern, breeding on lowland heath in Dorset, England. We take the novel approach of utilising the birds’ response to human disturbance, which resulted in much of the variation in density but had no direct impact on demographic rates. Within years, in sites with greater density there were smaller mean chick masses, lower post-fledging survival, and higher rates of nestling mortality attributed to starvation. The effects on clutch size and fledging success were confounded by the area of grassland within a site. There was no effect on brood size. Density dependence also operated within sites between years: as density increased there were reductions in mean chick mass and post-fledging survival, while nestling mortality attributed to starvation increased. Density-dependent effects on clutch size were only weakly regulatory, whereas density-dependent starvation and post-fledging mortality rates contributed strongly to differences in overall breeding output. Heavier chicks (when 7 days old) were significantly more likely to fledge and less likely to starve. Broods with heavier chicks were more likely to supply recruits to the breeding population. Nestling mass was not a factor in survival in the immediate post-fledging period, suggesting that density-dependent processes act independently on this stage. We conclude that the number of birds per hectare of suitable habitat is a valid means of expressing density, and that habitat acts as a surrogate for food abundance through which density dependence operates on the woodlark population.     

Achieving Better Estimates of Greater Sage-Grouse Chick Survival in Utah

Abstract: Declining sage-grouse (Centrocercus urophasianus) populations may be characterized by poor recruitment largely attributed to low chick survival. However, few published studies have explicitly examined factors that influence chick survival. We used a suture method to radiomark 1-2-day-old sage-grouse chicks (n = 150) in 2005-2006 on Parker Mountain in south-central Utah, USA, and monitored their survival to 42 days. We modeled effects of year, hatch date, chick age, brood-female age, brood-mixing, and arthropod abundance on chick survival. Our best model revealed an average survival estimate of 0.50 days to 42 days, which is the highest level ever documented for this long-lived species. Brood-mixing occurred in 21% (31/146) of chicks and 43% (18/42) of broods we studied. Moreover, yearling females had more chicks leave their broods than did adults. We found that survival may be higher among chicks that switch broods compared to those that stayed with their natal mother until fledging. Thus, brood-mixing may be an adaptive strategy leading to increased sage-grouse chick survival and higher productivity, especially among chicks born to yearling females. Our findings also indicate that arthropod abundance may be an important driver of chick survival, particularly during the early brood-rearing period and, therefore, sage-grouse populations may benefit from a management strategy that attempts to increase arthropod abundance via brood habitat management.     

Climate change and annual survival in a temperate passerine: partitioning seasonal effects and predicting future patterns

Predicting climate change impacts on population size requires detailed understanding of how climate influences key demographic rates, such as survival. This knowledge is frequently unavailable, even in well‐studied taxa such as birds. In temperate regions, most research into climatic effects on annual survival in resident passerines has focussed on winter temperature. Few studies have investigated potential precipitation effects and most assume little impact of breeding season weather. We use a 19‐year capture–mark–recapture study to provide a rare empirical analysis of how variation in temperature and precipitation throughout the entire year influences adult annual survival in a temperate passerine, the long‐tailed tit Aegithalos caudatus. We use model averaging to predict longer‐term historical survival rates, and future survival until the year 2100. Our model explains 73% of the interannual variation in survival rates. In contrast to current theory, we find a strong precipitation effect and no effect of variation in winter weather on adult annual survival, which is correlated most strongly to breeding season (spring) weather. Warm springs and autumns increase annual survival, but wet springs reduce survival and alter the form of the relationship between spring temperature and annual survival. There is little evidence for density dependence across the observed variation in population size. Using our model to estimate historical survival rates indicates that recent spring warming has led to an upward trend in survival rates, which has probably contributed to the observed long‐term increase in the UK long‐tailed tit population. Future climate change is predicted to further increase survival, under a broad range of carbon emissions scenarios and probabilistic climate change outcomes, even if precipitation increases substantially. We demonstrate the importance of considering weather over the entire annual cycle, and of considering precipitation and temperature in combination, in order to develop robust predictive models of demographic responses to climate change. Synthesis Prediction of climate change impacts demands understanding of how climate influences key demographic rates. In our 19‐year mark‐recapture study of long‐tailed tits Aegithalos caudatus, weather explained 73% of the inter‐annual variation in adult survival; warm springs and autumns increased survival, wet springs reduced survival, but winter weather had little effect. Robust predictions thus require consideration of the entire annual cycle and should not focus solely on temperature. Unexpectedly, survival appeared not to be strongly density‐dependent, so we use historical climate data to infer that recent climate change has enhanced survival over the four decades in which the UK long‐tailed tit population has more than doubled. Furthermore, survival rates in this species are predicted to further increase under a wide range of future climate scenarios.     

The Effects of Landscape Characteristics on Northern Bobwhite Density

The northern bobwhite (Colinus virginianus) is an ecologically and economically valuable species in the United States. Managers rely on autumn density estimates to set harvest regulations, balancing the interests of hunters and long-term bobwhite population viability. Spatial capture-recapture (SCR) is a useful framework for estimating population size and modeling spatial variation in density. We used SCR to quantify the effect of landscape structure on spatial variation in density for a population of bobwhites on the Di-Lane Wildlife Management Area in Waynesboro, Georgia, USA. Without additional telemetry or nesting data, we were also able to estimate a spatially explicit metric of productivity. To sample the population, we deployed a fixed array of 395, 262, and 268 funnel traps in 2016, 2017, and 2018, respectively. We estimated age structure, with the highest density of juveniles (0.32 birds/ha, 95% CI = 0.28–0.37) and adults (0.10 birds/ha, 95% CI = 0.08–0.12) estimated in 2016. In our top model, density was negatively related to the proportion of closed canopy hardwoods. To increase bobwhite density on the landscape, managers should reduce the amount of closed canopy hardwood forest. Furthermore, the spatially explicit age ratio we estimated could be used to target management towards increasing the recruitment of chicks into the autumn population. An SCR approach may require additional logistical and financial resources relative to other data collection methods, but it makes modeling spatial variation in density straightforward and can be used to gather data to simultaneously understand population structure, vital rates, and movement. © 2021 The Wildlife Society.     

Impact of weather and climate variation on Hoopoe reproductive ecology and population growth

Preserving peripheral populations is a key conservation issue because of the adaptive potential to environmental change they provide for the species as a whole. Yet, peripheral populations are often small and isolated, i.e. more vulnerable to stochastic events and prone to extinction. We studied a peripheral population of Hoopoe (Upupa epops), a rare insectivorous farmland bird, in the Swiss Alps. We first investigated the effect of weather variation on food provisioning to chicks by Hoopoe parents. Second, while accounting for density-dependence, we tested the extent to which breeding success is governed by weather circumstances and assessed the possible consequences of climate variation on population growth. Provisioning rate and provisioned prey biomass were negatively affected by adverse weather (cool, rainy days), were higher in males and also increased with brood size. Much smaller proportions of molecrickets (Gryllotalpa gryllotalpa; the most profitable prey locally, constituting 93% of chicks’ food biomass) were provisioned on days with adverse weather, irrespective of brood size. Rainfall prior to hatching and during the first days of chick life had a negative impact on their survival, and there was a positive effect of temperature on chick survival just before fledging. Reproductive output was negatively affected by precipitation during the hatching period, but was enhanced by warm temperature just before hatching and in the last days before fledging. Our model showed that the variable reproductive output has a strong impact on the population growth: a succession of adverse, rainy springs would cause a rapid decline of the population. This case study confirms that conservation efforts may be obliterated if risks linked to increasing climate variability are not properly accounted for in the management of small peripheral populations.     

Exclusion of ground predators improves Northern Lapwing Vanellus vanellus chick survival

Many farmland‐breeding wader species have declined across Europe, probably due to reductions in reproductive output caused by high nest losses as a result of agriculture or predation, or low chick survival between hatching and fledging. Most studies have focused on nest failures, and the factors affecting post‐hatching survival of chicks are poorly known. In an experimental approach, we fenced parts of the arable foraging areas of Northern Lapwing Vanellus vanellus families to quantify chick survival simultaneously in the presence and absence of ground predators. Lapwing chicks were radiotagged to estimate survival probabilities by daily locations, applying multistate capture–recapture models. During the night, chick survival was considerably lower outside fenced plots than within. During the day, chick survival was higher than at night and did not differ between protected and unprotected plots. This suggests that nocturnal ground predators such as Red Foxes Vulpes vulpes were responsible for a significant proportion of chick mortality. Cumulative survival probability from hatching to fledging was 0.24 in chicks within fenced plots, but virtually zero in chicks outside fenced plots. In farmland, temporary electric fences can be effective in minimizing the impact of ground predators and offer a promising short‐term method to increase fledging success of precocial birds.     

Simulating northern bobwhite population responses to nest predation,nesting habitat,and weather in south Texas

Nest predation is thought to be one of the major factors limiting northern bobwhite (Colinus virginianus) populations. We examined the relative impact of altering nest-predation rate, nesting habitat, and weather (i.e., temp and precipitation) on northern bobwhite population dynamics in a hypothetical 15,000-ha subtropical-rangeland ecosystem in south Texas using a simulation model. The systems model consisted of a 3-stage (i.e., eggs, juv, and ad) bobwhite population with dynamics influenced by variables affecting production, recruitment, nest predation, and mortality. We based model parameters on data collected from a 3-yr nest-predator study employing infrared-camera technology, from ongoing field research using a radio-marked population of wild bobwhites, and from the literature. The baseline simulated bobwhite population dynamics corresponded closely to empirical data, with no difference between medians of simulated (n = 30 yr) and observed bobwhite age ratios over a 28-yr period. Similarly, a time-series comparison of simulated and observed age ratios showed most (89%) observed values fell within the 5th and 95th percentiles of the simulated data over the 28-yr period. We created simulated population scenarios representing 1) baseline historical conditions, 2) predator control, 3) low precipitation, 4) low precipitation with predator control, 5) high temperature, 6) high temperature with predator control, 7) reduced nest-clump availability, and 8) reduced nest-clump availability with predator control that resulted in considerably different median bobwhite densities over 10 yr. For example, under simulated predator control, populations increased by about 55% from the baseline scenario, whereas under simulated reduced nest-clump availability, populations decreased by about 75% from the baseline scenario. Comparisons of time-series for each scenario showed that reduced nest-clump availability, low precipitation, and high temperature reduced bobwhite densities to a larger degree compared to a natural nest predation rate. Reduced nest-clump availability resulted in the most substantial decline of simulated bobwhite densities. Simulations suggested that management efforts should focus on maintaining adequate nest-clump availability and then possibly consider nest predator control as a secondary priority. © 2010 The Wildlife Society     

Golden Plover Pluvialis apricaria breeding success on a moor managed for shooting Red Grouse Lagopus lagopus

Capsule The best estimate of breeding success was a mean of 0.57 fledglings per pair, which when combined with adult survival rates, successfully explained the observed population trend.

Aims To quantify Golden Plover breeding success on a moor managed for shooting Red Grouse Lagopus lagopus.

Methods An intensive study recorded the fate of individual Golden Plover nests and, using radiotelemetry, chicks. The factors associated with mortality were examined, allowing the construction of a model of breeding success. Adult survival was estimated from return rates of colour-ringed birds.

Results Estimated rates of daily nest survival during laying (0.8636) were significantly lower than during incubation (0.9913). The daily survival rate of chicks less than nine days (0.8868) was significantly lower than for older chicks (0.9792). A population model based on these parameters overestimated the rate of nest losses, but accurately described brood survival and fledging success. Although predation rates were low, poor survival of young chicks through starvation or exposure suggest other factors were limiting breeding success at the study site.

Conclusions Predation rates of Golden Plover nests and chicks can be low on moorlands managed for shooting Red Grouse. However, in the absence of predation, other factors may still reduce chick survival and limit breeding success.     

长白山花尾榛鸡繁殖成功率的研究

１９８６～１９９５年,对长白山花尾榛鸡的繁殖率进行了研究。无线电遥测的结果表明,花尾榛鸡的孵化率为６５５％（ｎ＝５）,繁殖成功率为２０９％（ｎ＝４）,幼鸟成活率３７５％（ｎ＝３）。花尾榛鸡家族群的幼鸟数随日龄增加而减少,幼鸟日龄为０～２５日时死亡率较高,２５日龄后的死亡率显著减少。１０年花尾榛鸡的繁殖成功率指数的变化与６月的降水量及＞１ｍｍ的降水天数呈显著的负相关（Ｐ＜００５,Ｐ＜００２５）,说明育雏初期降水对幼鸟成活率的影响较大。     

Effects of range position,inter-annual variation and density on demographic transition rates of <Emphasis Type="Italic">Hornungia petraea</Emphasis> populations

The central-marginal model assumes unfavourable and more variable environmental conditions at the periphery of a species’ distribution range to negatively affect demographic transition rates, finally resulting in reduced population sizes and densities. Previous studies on density-dependence as a crucial factor regulating plant population growth have mainly focussed on fecundity and survival. Our objective is to analyse density-dependence in combination with the effect of inter-annual variation and range position on all life stages of an annual plant species, Hornungia petraea, including germination and seed incorporation into the seed bank. As previous studies on H. petraea had revealed a pattern opposite to existing theory with lower population densities at the distribution centre in Italy than at the periphery in Germany, we hypothesised that (1) demographic transition rates are lower, (2) the inter-annual variation in demographic transition rates is higher and (3) the intensity of density-dependence is weaker in Italy than in Germany. To analyse demographic transition rates, we used an autoregressive covariance strategy for repeated measures including density and inter-annual variation. All the three hypotheses were confirmed, but the impact of range position, density-dependence and inter-annual variation differed among the transition steps. All transition rates except fecundity were higher in the German populations than in the Italian populations. Germination rate and incorporation rate into the seed bank were strongly density-dependent. Central populations showed a larger inter-annual variation in fecundity and winter survival rate. Winter survival rate was the only transition step with a stronger density-dependence in peripheral populations. In most cases, these differences between distribution centre and periphery would not have emerged without taking density-dependence and inter-annual variation into account. We conclude that including range position, inter-annual variation and density-dependence in one single statistical model is an important tool for the interpretation of demographic patterns regarding the central-marginal model. Electronic Supplementary Material Supplementary material is available for this article at     

Costs and benefits of colony size vary during the breeding cycle in Black-headed Gulls Chroicocephalus ridibundus

We studied the effects of colony size on individual reproductive success in a multi-site population of Black-headed Gulls Chroicocephalus ridibundus where colony size ranged from 10 to 5,000 pairs. By focusing on family size, the number of chicks attended by individually marked parents, and accounting for between-individual variation, we detected a negative colony-size effect during the very first days of life of the chicks that was compensated by a subsequent increase in the proportion of surviving chicks with colony size. We suggest that this result originates in the interplay between overcrowding costs acting on hatching success, and benefits of colonial breeding, most probably more efficient food-searching (foraging enhancement), acting on chick survival. However, the frequency of complete colony failure increased with decreasing colony size. Taking this hazard risk into account yielded a corrected estimate of the effect of colony size on breeding success, and indicated that the largest colonies were the most productive. This pattern is congruent with the previous finding that larger colonies are more attractive to dispersing breeders.     

Precipitation and Reproduction are Negatively Associated with Female Turkey Survival

Understanding how reproductive tradeoffs act in concert with abiotic elements to affect survival is important for effective management and conservation of wildlife populations, particularly for at-risk or harvested species. Wild turkeys (Meleagris gallopavo) are a high-interest species for consumptive and non-consumptive uses, and female survival is a primary factor influencing turkey population dynamics. We radio-tracked and collected survival data on 140 female Merriam's wild turkeys (M. g. merriami) in the northern Black Hills, South Dakota, USA, 2016–2018. We developed and compared a set of candidate models to evaluate how nest incubation, brood rearing, and precipitation could be associated with female survival. Increased time spent incubating was associated with reduced female survival. Additionally, daily precipitation was associated with reduced survival of incubating females. Seasonal survival was lowest during spring and winter. A female that did not incubate a nest was predicted to have a higher rate of annual survival (0.53, 85% CI = 0.48–0.59) than a female that incubated a single nest (0.47, 85% CI = 0.42–0.53). Despite the relative proximity of population segments, we estimated that annual survival for nesting and non-nesting females was lower in the northern Black Hills compared to annual female survival in the southern Black Hills, underscoring the need for region-specific data when possible. © 2020 The Wildlife Society.