Brett K. Sandercock

Genetic similarity between mates and extra-pair parentage in three species of shorebirds

Matings between close relatives often reduce the fitness of offspring, probably because homozygosity leads to the expression of recessive deleterious alleles. Studies of several animals have shown that reproductive success is lower when genetic similarity between parents is high, and that survival and other measures of fitness increase with individual levels of genetic diversity. These studies indicate that natural selection may favour the avoidance of matings with genetically similar individuals. But constraints on social mate choice, such as a lack of alternatives, can lead to pairing with genetically similar mates. In such cases, it has been suggested that females may seek extra-pair copulations with less related males, but the evidence is weak or lacking. Here we report a strong positive relationship between the genetic similarity of social pair members and the occurrence of extra-pair paternity and maternity (‘quasi-parasitism’) in three species of shorebirds. We propose that extra-pair parentage may represent adaptive behavioural strategies to avoid the negative effects of pairing with a genetically similar mate.

Estimation of Demographic Parameters from Live-Encounter Data: a Summary Review

Abstract Estimation of demographic parameters is central to research questions in wildlife management, conservation, and evolutionary ecology. I review the 7 major classes of mark–recapture models that investigators can use to estimate apparent survival and other parameters from live-encounter data. Return rates are the product of 4 probabilities: true survival (S), site fidelity (F), site propensity (δ), and true detection (p*). Cormack-Jolly-Seber (CJS) models improve upon return rates by separating apparent survival (φ = S × F) from the probability of encounter (p = δ × p*). The main drawback to mark–recapture models based on live-encounter data is that the complement of apparent survival (1 − φ) includes losses to mortality and to permanent emigration, and these 2 ecological processes are difficult to disentangle. Advanced mark–recapture models require additional sampling effort but estimate apparent survival with greater precision and less bias, and they also offer estimates of other useful demographic parameters. Time-since-marking or transient models control for individuals not encountered after the occasion they are first marked, a common feature of wildlife populations. Temporal symmetry models combine forward- and reverse-time modeling to estimate recruitment (f) and the finite rate of population change (λ). Multi-strata models include dynamic categorical information and offer state-specific estimates of apparent survival and encounter rates, as well as probabilities of changing states (Ψ). Robust design models subdivide sampling occasions into shorter periods, and they partition encounter rates (p) into estimates of temporary emigration (γ = 1 − δ) and true detection (p*). Joint models combine live encounters with other sources of information, including dead-recovery data, and decompose apparent survival into estimates of true survival (S) and site fidelity (F). Cormack-Jolly-Seber and multi-strata models have a large literature, but many of the advanced models have not yet received widespread use. In the future, wildlife ecologists should design field studies that take advantage of the best possible statistical procedures now that a range of alternative models and software tools are available.

Is hunting mortality additive or compensatory to natural mortality? Effects of experimental harvest on the survival and cause‐specific mortality of willow ptarmigan

1. The effects of harvest on the annual and seasonal survival of willow ptarmigan Lagopus lagopus L. were tested in a large-scale harvest experiment. Management units were randomly assigned to one of three experimental treatments: 0%, 15% or 30% harvest. Seasonal quotas were based on the experimental treatment and estimates of bird density before the hunting season. Survival rates and hazard functions for radio-marked ptarmigan were then estimated under the competing risks of harvest and natural mortality. 2. The partially compensatory mortality hypothesis was supported: annual survival of ptarmigan was 0·54 ± 0·08 SE under 0% harvest, 0·47 ± 0·06 under 15% harvest, and was reduced to 0·30 ± 0·05 under 30% harvest. Harvest mortality increased linearly from 0·08 ± 0·05, 0·27 ± 0·05 and 0·42 ± 0·06 from 0% to 30% harvest, whereas natural mortality was 0·38 ± 0·08, 0·25 ± 0·05 and 0·28 ± 0·06 under the same treatments. 3. Realized risk of harvest mortality was 0·08-0·12 points higher than our set harvest treatments of 0-30% because birds were exposed to risk if they moved out of protected areas. The superadditive hypothesis was supported because birds in the 30% harvest treatment had higher natural mortality during winter after the hunting season. 4. Natural mortality was mainly because of raptor predation, with two seasonal peaks in fall and spring. Natural and harvest mortality coincided during early autumn with little potential for compensation during winter months. Peak risk of harvest mortality was 5× higher than natural mortality. Low natural mortality during winter suggests that most late season harvest would be additive mortality. 5. Environmental correlates of natural mortality of ptarmigan included seasonal changes in snow cover, onset of juvenile dispersal, and periods of territorial activity. Natural mortality of ptarmigan was highest during autumn movements and nesting by gyrfalcons Falco rusticolus L. Mortality was low when gyrfalcons had departed for coastal wintering sites, and during summer when ptarmigan were attending nests and broods. 6. Our experimental results have important implications for harvest management of upland gamebirds. Seasonal quotas based on proportional harvest were effective and should be set at ≤ 15% of August populations for regional management plans. Under threshold harvest of a reproductive surplus, 15% harvest would be sustainable at productivity rates ≥ 2·5 young per pair. Impacts of winter harvest could be minimized by closing the hunting season in early November or by reducing late season quotas.

LIFE HISTORY STRATEGIES IN EXTREME ENVIRONMENTS: COMPARATIVE DEMOGRAPHY OF ARCTIC AND ALPINE PTARMIGAN

Arctic and alpine habitats are extreme environments characterized by short breeding seasons, cold temperatures, limited food availability, and potentially high predation rates. Stringent ecological conditions are likely to have important consequences for the evolution of life history traits, but direct empirical tests are few. We compare the demog- raphy of three populations of ptarmigan on an environmental gradient spanning alpine, subalpine, and arctic habitats. Female Willow Ptarmigan (Lagopus lagopus) and White- tailed Ptarmigan (L. leucurus) breeding at subalpine and alpine sites had smaller clutches and lower probabilities of nesting success, fledging success, and renesting than Willow Ptarmigan nesting at a low-elevation arctic site. Annual fecundity, measured as female fledglings per breeding female, did not overlap among the three populations and was ranked: alpine (0.40 6 0.08, mean 6 SE, 95% CI 5 0.26-0.58) , subalpine (1.33 6 0.10, 1.13- 1.54) , arctic (2.04 6 0.18, 1.68-2.39). There was a nonsignificant trend for apparent survival rates (f) of breeding females to vary in the opposite direction: alpine (0.46 6 0.04) . subalpine (0.43 6 0.03) . arctic (0.37 6 0.06). Population growth rates predicted significant declines for the alpine population ( l5 0.65 6 0.07, 95% CI 5 0.52-0.79), but not the subalpine ( l5 1.00 6 0.07, 0.86-1.14) or arctic populations ( l5 1.13 6 0.20, 0.78-1.54). The adjusted estimates of survival necessary to sustain a stationary population indicated that actual variation in female survival was more pronounced than the observed rates: alpine (0.71) . subalpine (0.43) . arctic (0.33). Together, the fecundity and survival values provide evidence that even congeneric populations can exhibit a continuum between high reproductive and survivor life history strategies. Variation in ptarmigan life history traits was consistent with population differences in predation rates on eggs and breeding females, and it was not related to duration of the breeding season, climatic conditions, or food availability. Ptarmigan demography also covaried with body size, but not in the predicted pattern. Overall, the life history strategies of ptarmigan are consistent with our current understanding of the impacts of environmental factors upon life history variation in passerine songbirds.

ANNUAL SURVIVAL RATES OF WINTERING SPARROWS: ASSESSING DEMOGRAPHIC CONSEQUENCES OF MIGRATION

Abstract The demographic consequences of migration have important implications for both evolutionary ecology and conservation biology. We investigated local survival rates for six populations of sparrows at a wintering site. Recent developments in mark–recapture statistics were applied to a 13 year dataset with large numbers of marked individuals (n = 1,632 to 4,394). The study taxa were closely related, and included one resident species (Song Sparrow [Melospiza melodia gouldii]), one short-distance migrant (“Puget Sound” White-crowned Sparrow [Zonotrichia leucophrys pugetensis]), two moderate-distance migrants (Lincolns [Melospiza lincolnii] and Fox [Passerella iliaca] sparrow), and two long-distance migrants (“Gambels” White-crowned [Zonotrichia leucophrys gambelii] and Golden-crowned [Zonotrichia atricapilla] sparrow). A literature review demonstrated a cline in fecundity among these sparrows: resident and short-distance migrants laid multiple clutches of few eggs, whereas long-distance migrants tended to produce one large clutch. Annual rates of local survival were low in the interval after first capture (<0.35), possibly because of variation in true survival, site-fidelity, presence of transients and heterogeneity of capture. Estimates of local survival among birds that returned at least once were more robust and were comparable among Song (0.558 ± 0.054 SE), Puget Sound White-crowned (0.461 ± 0.026), Lincolns (0.456 ± 0.066), Fox (0.352 ± 0.0), Golden-crowned (0.422 ± 0.023) and Gambels White-crowned (0.432 ± 0.0) sparrows. Estimates of survivorship for Lincolns and Fox sparrows are among the first values available for those species. Local survival was not higher among resident than migratory taxa, nor did it covary with migration distance among migratory species. These results did not support the time-allocation hypothesis of Greenberg (1980), but are consistent with aspects of bet-hedging theory. While these analyses have potential implications for conservation of migratory birds, further work is required to establish whether these patterns are applicable to Neotropical migrants.

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.

The effects of age and sex on the apparent survival of Kentish Plovers breeding in southern Turkey

Abstract Accurate estimates of annual survival are necessary for conservation of threatened species of migratory birds. We studied a large, stable population of Kentish Plovers (Charadrius alexandrinus) breeding in southern Turkey (36°43′N, 35°03′E) for five breeding seasons (1996–2000). Kentish Plovers of Eurasia and the conspecific Snowy Plover of North America are a species of conservation concern. We captured 2077 birds, and used time since marking models to estimate apparent survival (ϕ) and encounter rates (p) for juvenile and adult plovers. Return rates of young banded in their natal year were low (4%, 52 of 1176) and most philopatric young were recaptured as yearlings (69%, 36 of 52). Low return rates of shorebird young can be attributed to post-hatching mortality if apparent survival rates are ranked: chicks < fledglings = adults. We were unable to separate mortality from dispersal because apparent survival was ranked: chicks (ϕ̂1 = 0.08) < fledglings (ϕ̂1 = 0.15) < adults after banding (ϕ̂1 = 0.59) < adults in later intervals (ϕ̂2+ = 0.64). Time since marking models gave improved estimates of the apparent survival of adults that were higher than return rates in other populations of Kentish Plovers, but lower than estimates of apparent survival for other Charadrius plovers. Sex-biased mating opportunities in Kentish Plovers were not explained by biased sex ratios at hatching or differential apparent survival among adults. Instead, male-biased adult sex ratios were explained, in part, by differential survival of juveniles and by higher encounter rates among adult males (p̂ = 0.84) than females (p̂ = 0.74). Our baseline estimates of apparent survival will assist assessments of population viability for Kentish and Snowy Plovers throughout their geographic range. Efectos de la Edad y del Sexo sobre la Supervivencia Aparente de Charadrius alexandrinus en Áreas de Cría en el Sur de Turquía Resumen. Contar con estimaciones exactas de la supervivencia anual es necesario para la conservación de las aves migratorias amenazadas. Estudiamos una población grande y estable de Charadrius alexandrinus en un área de cría del sur de Turquía (36°43′N, 35°03′E) durante cinco épocas reproductivas (1996–2000). Charadrius alexandrinus es una especie con un estado de conservación preocupante tanto en Eurasia como en Norte América. En este estudio capturamos 2077 aves y empleamos modelos del tiempo transcurrido desde el marcado para estimar las tasas de supervivencia aparente (ϕ) y de encuentro (p) para individuos juveniles y adultos. Las tasas de regreso de juveniles anillados a su área de nacimiento fueron bajas (4%, 52 de 1176), y la mayoría de los individuos filopátricos fueron recapturados cuando tenían un año de edad (69%, 36 de 52). Las bajas tasas de regreso de los pichones de aves playeras pueden deberse a mortalidad post-eclosión si las tasas de supervivencia aparente son menores en los pichones que en los volantones y adultos, y si estos dos últimos tienen tasas de supervivencia similares. No estuvimos en capacidad de distinguir entre mortalidad y dispersión debido a que la supervivencia aparente fue mínima en los pichones (ϕ̂1 = 0.08) y subsecuentemente mayor en volantones (ϕ̂1 = 0.15), en adultos luego de ser marcados (ϕ̂1 = 0.59) y en adultos en intervalos posteriores (ϕ̂2+ = 0.64). Los modelos basados en el tiempo transcurrido desde el marcado arrojaron mejores estimados de la supervivencia aparente de los adultos. Estos estimados fueron mayores que las tasas de regreso estimadas para otras poblaciones de C. alexandrinus, pero menores que la supervivencia aparente estimada para otras especies de Charadrius. Las oportunidades de apareamiento sesgadas de acuerdo al sexo observadas en C. alexandrinus no se explicaron por cocientes de sexos sesgados al momento de la eclosión, ni por diferencias en la supervivencia aparente de individuos adultos. En cambio, los cocientes de sexos sesgados hacia los machos evidentes en los adultos se explicaron en parte por diferencias en la supervivencia de los juveniles y por tasas de encuentro mayores entre machos adultos (p̂ = 0.84) en comparación con las hembras (p̂ = 0.74). Nuestros estimados de la supervivencia aparente representan una base que contribuirá a examinar la viabilidad de las poblaciones de C. alexandrinus a través de su rango de distribución.

Age‐Specific Survival and Probable Causes of Mortality in Female Lesser Prairie‐Chickens

Abstract Long-term population declines and habitat reductions have increased concern over the status of the lesser prairie-chicken (Tympanuchus pallidicinctus). Robust estimates of demographic parameters are essential for identifying population declines and planning effective management. We evaluated the effects of age and season on the survival of female lesser prairie-chickens at 2 sites in southwestern Kansas, USA. Using telemetry data from a 7-year field study (from 1997 to 2003), we estimated seasonal (Apr–Sep) and annual (Apr–Mar) survival. We also examined daily survival rates of females attending nests during the 26-day incubation period and young during the 14-day early brood-rearing period. We evaluated the probable mortality causes of radiomarked birds by examining evidence at recovery sites. We captured 227 female lesser prairie-chickens (87 yearlings, 117 ad, and 23 age undetermined) and fitted them with radiotransmitters. Estimates of 12-month survival were lower among yearlings (Ŝ12 = 0.429, SE = 0.117) and adults at site I (Ŝ12 = 0.302, SE = 0.080) than among yearlings (Ŝ12 = 0.588, SE = 0.100) and adults at site II (Ŝ12 = 0.438, SE = 0.083). The patterns in timing of mortality and age-specific 6-month survival were consistent with those of 12-month estimates at site I from 1998 to 2002, with a peak in mortality during May and June. Females tending to nests or to prefledged chicks had lower daily survival (DŜRtend = 0.993, SE = 0.001) than females not involved in these activities (DŜRfailed-breeder = 0.997, SE = 0.002). We recorded 92 mortalities from April 1997 to March 2003, and 59% and 11% were attributed to predation by mammals and raptors, respectively. Our research suggests that predation during the nesting season can have a major impact on lesser prairie-chicken demography, and conservation efforts should focus on enhancing female survival during the nesting and brood-rearing seasons.

Optimizing Radio Retention and Minimizing Radio Impacts in a Field Study of Upland Sandpipers

Abstract Two challenges in wildlife telemetry are optimizing the duration of transmitter attachment and minimizing the impacts of radios on the behavior and demography of the study animal. We tested 4 methods of radio attachment for a breeding population of upland sandpipers (Bartramia longicauda) under natural conditions at a tallgrass prairie site in Kansas, USA. To estimate radio retention and weekly survival rates, we used the nest survival model of Program MARK. Radio retention was lowest at the start and the end of the breeding period. The expected duration of radio retention was 1.8 years for a leg-loop harness, 40 days for radios glued to clipped feathers, 26 days for radios glued directly to feathers, and 7 days for radios glued to bare skin. Few radiomarked birds died during our study, but 4 of 8 mortality events were discovered within one week of radiomarking. Both glue and harnesses increased predation risk immediately after radio attachment. The weekly probability of survival was high after a 1-week acclimation period, and the expected survival for a 10-week breeding period was similar in males and females. Attachment of radios with glue had no effect on annual return rates. However, attachment of radios with leg harnesses resulted in lower return rates among radiomarked birds than birds without radios. Radios attached with glue were shed in <1 year but radios attached with harnesses were retained for up to 1–2 years. Our results indicate a tradeoff between optimizing radio retention and minimizing impacts on demography. Glue techniques had retention rates that were suitable for only short-term studies, but attachment with glue had no long-term effect on annual return rates. Leg harnesses provided effective radio retention that had little effect on survival rates during the stationary breeding period, but resulted in lower annual return rates. Robust estimates of radio retention and survival will assist researchers in selecting attachment techniques that best meet the study goals of future telemetry projects.

Estimating rates of population change for a neotropical parrot with ratio, mark-recapture and matrix methods

Robust methods for estimating rates of population change ( u ) are necessary for applied and theoretical goals in conservation and evolutionary biology. Traditionally, u has been calculated from either ratios of population counts (observed u or u obs ), or population models based on projection matrices (asymptotic u or u asy ,). New mark-recapture methods permit calculation of u from mark-resighting information alone (realized u or u rea ), but empirical comparisons with other methods are rare. In this paper, rates of population change were calculated for a population of green-rumped parrotlets ( Forpus passerinus ) that have been studied for more than a decade in central Venezuela. First, a ratio method based on counts of detected birds was used to calculate u obs. Next, a temporal symmetry method based on mark-recapture data (i.e. the u -parameterization introduced by Pradel, 1996) was used to calculate u rea . Finally, a stage-structured matrix model based on state-specific estimates of fecundity, immigration, local survival, and transition rates was used to calculate u asy . Analyses were conducted separately for females and males. Overall values of u from the three methods were consistent and all indicated that the finite rate of population change was not significantly different from 1. Annual values of u from the three methods were also in general agreement for a majority of years. However, u rea from the temporal symmetry method had the greatest precision, and apparently better accuracy than u asy . Unrealistic annual values of u asy could have been due to poor estimates of the transitional probability of becoming a breeder ( é ) or to a mismatch between the actual and the asymptotic stable stage distribution. In this study, the trade-off between biological realism and accuracy was better met by the temporal symmetry than the matrix method. Our results suggest that the temporal symmetry models can be applied with confidence to populations where less information may be available.