Individual Papers

8:55-9:20 AM Effects of Spring conditions on breeding propensity of Greater Snow Goose females - Eric Reed, Gilles Gauthier & Jean-Francois Giroux Breeding propensity, the probability that a sexually mature adult will breed in a given year, is an important determinant of annual productivity. It is also one of the least known demographic parameters in vertebrates. Although recent methodological advances in mark-recapture methods have allowed the estimation of breeding propensity for some bird species, little is known about factors responsible for temporal variation in this parameter. We studied the relationship between breeding propensity and conditions encountered on the spring staging areas and the breeding grounds in Greater Snow Geese (Chen caerulescens atlantica), a long distance migrant that breeds in the High Arctic. We used an Robust Design approach where classic capture histories were combined with auxiliary information from radio-marked birds and nest survey data to estimate breeding propensity over a 7-year period. More specifically, mark-recapture data was used to estimate probabilities of capture if alive and present in the superpopulation, and information from radio-marked birds was used to estimate probabilities of capture given presence in the sampled area. We also had to correct our estimates for nest success, because failed nesters emigrated from the sampled area, and incomplete fidelity to brood rearing areas (i.e. sampling area). We tested the effects of spring snow cover and a spring conservation hunt on breeding propensity using a weighted least squares approach. We also used an empirical variance-components approach and determined that true temporal variation in breeding propensity was considerable (mean breeding propensity: 0.574 [95% CI considering only process variation: 0.13 to 1]). Spring snow cover was negatively related to breeding propensity (βsnow = -2.05 ± 0.96 SE) and tended to be reduced in years with a spring hunt (β = -0.78 ± 0.35). Nest densities on the breeding colony and fall young/adult ratio were good indices of breeding propensity, with nest densities being slightly more precise. These results suggest that environmental conditions and disturbance encountered during the pre-breeding period can have a significant impact on productivity of Arctic-nesting birds. 9:20-9:45 AM Earlier recruitment or earlier death? On assumptions of homogeneous survival rates in capture-recapture models to estimate recruitment - Emmanuelle Cam, Evan Cooch & Jean-Yves Monnat Realized patterns of age of recruitment observed in the breeding segment of populations are governed by the product of two demographic components: [survival probability from birth to age ]*[transition probability from state prebreeder to state first-time breeder at age ]. To again insight into selective pressures shaping age of recruitment, one may address temporal variation in age of first breeding and covariation with population size or social and environmental factors. This involves comparison among "groups" (e.g., cohorts) of individuals encountering different environmental conditions when they reach a given age as prebreeders. However, measures of recruitment based exclusively on data from the breeding segment of the population ignore the size of the pool of prebreeders (as opposed to transition probability). However, in a large number of species with deferred breeding, individuals are not encountered prior to breeding. Approaches to estimating age-specific recruitment probability in the absence of data from prebreeders using mark-recapture have been developed (Pradel and Lebreton 1999, Schwarz and Arnasson 2001, Williams et al. 2002). Unless the survival component of realized age-specific recruitment rates is known to be identical among the groups compared, inferences about the "cause" of variation in realized age of first breeding among groups are difficult: such differences may in fact result from differences in survival probability before individuals make the transition between states. Inferences about differences in realized recruitment rates among groups exclusively based on data from the breeding segment of the population reflect differences in recruitment probability under the assumption that there is no difference in prebreeder survival among these groups. We assessed the consequences of violations of this assumption on our perception of age-specific realized recruitment rates using numerical simulations; the scenarios considered correspond to various biological hypotheses about group-specific variation in survival and transition probabilities. Data were simulated under regular multistate models (Nichols and Kendall 1995) and truncated individual histories were then analyzed using the reverse-time approach (Pradel 1996) and the approach developed by Schwarz and Arnasson (2001). Depending on the scenario, realized recruitment was delayed or advanced compared to the underlying pattern of age-specific transition probabilities. We also addressed age-specific recruitment probability in a long-lived seabird species, the kittiwake (Rissa tridactyla) using a data set including data from prebreeders. We compared results from the reverse-time approach and the multistate approach, and showed that transition probability directly estimated or derived from measures of recruitment based on the breeding segment of the population are different. 9:45-10:10 AM Predictors of reproductive costs in Soay sheep: a multistate capture-recapture analysis - Giacomo Tavecchia, T. Coulson, B.J.T. Morgan, J. Pemberton, J. Pilkington & T.H. Clutton-Brock We investigate factors influencing the shape of the trade-off between survival and reproduction in female Soay sheep (Ovis aries). Multistate capture-recapture models are used to incorporate the state-specific recapture probability and to model the cost function directly from data on marked individuals. The cost of reproduction is identified as a quadratic function of the mother's age, being greatest for females breeding at the end of their first year and when more than 7 years old. Furthermore, the cost is only present during severe environmental conditions, when wet and cold winters coincide with high population density. Population density and winter severity negatively influence the probability of successfully breeding in the first year of life. Finally, the recapture probability depends on the breeding state: breeding females are virtually always recaptured while non-breeding individuals are not. The significant influence of the interaction between age and time on the phenotypic trade-off function might be responsible for maintaining cohort differences in demographic parameters. The use of multi-state capture-recapture analysis has allowed us to draw broader conclusions than earlier work, which was based on conditional methods of analysis 10:10-10:25 AM - break 10:25-10:45 AM Breeding cycles and reproductive investment: the case of the Leatherback sea turtle - Philippe Rivalan, R. Pradel, R. Choquet, J.-P. Briane, M. Girondot & A.C. Prevot-Julliard An important demographic parameter is the trade-off between current and future reproduction. A particular case is the relation between the number of years without reproduction and reproductive investment in years with reproduction.. We studied this trade-off in a long-lived species with intermittent breeding, the leatherback sea turtle, in French Guiana. Leatherback sea turtles lay several clutches within a reproductive year but reproduce every two or more years. Female leatherback sea turtles were captured, marked and recaptured when they lay eggs on nesting beach, from 1990 to 2002 (60,000 CMR events divided in two parts: (1) females marked from 1990 to 1994 with monel tags and subject to high tag-loss rate; (2) females marked from 1995 to 2002 with permanent pit-tags). We modeled intermittent breeding and reproductive investment as following: (1) We estimated the number of years without reproduction by using multistate models incorporating several non-observable states using the software M-Surge (Choquet et al. 2003). We included tag-loss probabilities in transition matrices for females marked from 1990 to 1994. (2) We assessed investment in reproduction (i.e., number of clutches) by estimating the duration of presence of females on the beach. This duration is equivalent to a stopover duration of migrating birds. We estimated this annual stopover duration of females on the beach using the software SODA (Shaub et al. 2001). We found two breeding strategies which have the same fitness, characterized by the number of years without reproduction (2 or 3) and the number of clutches within reproductive years. However, such strategies are not fixed for a given female. 10:45-11:05 AM Modelling senility and dispersal of Red deer - Ted Catchpole, T.N. Coulson, Y. Fan, & B.J.T. Morgan Red deer(Cervus elaphus) on the island of Rum have been closely studied for many years. In particular, this has resulted in an extensive mark-recapture-recovery (mrr) data set. Models for these data need an elaborate age-structure for survival, because deer react differently to environmental factors at different stages of their lives. An additional interesting feature of the data is that animals may leave the study area. Thus we are interested not only in modelling deer survival, but also deer dispersal. Our modeling approach is a classical statistical one. The two sexes need to be considered separately. Within each sex, we use standard likelihood tools and information criteria to identify age-classes, separately for survival and dispersal. Within each age-class, the relevant probability does not vary over the ages desribed by that class, with the exception of the oldest age-class for survival. This then allows us to undertake logistic regressions of the relevant age-class probabilities on a mixture of environmental and individual covariates. Senility, a gradual decline in survival probability with age, is described by means of a logistic regression on age within the oldest survival age-classes for males and females. The final models that we select for males and for females have an attractive simplicity. They demostrate clearly the differences that exist between males and females, and may be used for predicting future behaviour, and the effects of alternative management policies. The work of this paper is a natural extension of the models and model-selection procedures that have been developed for Soay sheep (Ovis aries) in Catchpole et al (2000) and Coulson et al (2001). The present work builds on the modelling of male red-deer alone by Catchpole et al (2002), and the modelling of both sexes in Fan et al (2002). 11:05-11:25 AM Assessing senescence patterns in populations of large mammals - Jean-Michel Gaillard & Anne Viallefont Theoretical models such as Gompertz and Weibull models are commonly used to study senescence in survival for humans (Olshansky & Carnes 1997) and laboratory or captive animals (Ricklefs 2000) for which a complete follow up of individuals is available. For wild populations of vertebrates, senescence in survival has more commonly been assessed by fitting simple linear or quadratic relationships between survival and age (e. g., McDonald et al. 1996, Newton and Rothery 1997, Nichols et al. 1997, Loison et al. 1999). By using appropriate constraints on survival parameters in Capture-Mark-Recapture (CMR) models, we propose a first analysis of the suitability of Gompertz and Weibull models for describing aging-related mortality in free-ranging populations of ungulates. We first show how to handle Gompertz and Weibull models in the context of CMR analyses. Then we perform a comparative analysis of senescence patterns in both sexes of two ungulate species highly contrasted according to the intensity of sexual selection. Evolutionary implications of our results are discussed. 11:25-11:45 AM Breeding site-fidelity and survival estimation of a migratory songbird: implications for conservation, life-history and study designs - Duane Diefenbach, M.R. Marshall, L. Wood, & R. Cooper We used data from a 5-year banding study of 423 Prothonotary Warblers (Protonotaria citrea) from the White River National Wildlife Refuge, Arkansas, USA to estimate annual apparent survival rates of adults. Also, we documented inter-annual changes in the placement of breeding territories to estimate emigration rates and distances moved. Recognizing that the apparent survival estimates included both survival and permanent emigration, and possibly temporary emigration, we simulated these movement patterns over a range of true survival rates (0.3 - 0.9) to estimate the bias introduced by emigration if apparent survival estimates were used as true survival rate estimates. The simulations suggested that the observed warbler movements resulted in apparent survival estimates, compared to true survival rates, being 25% and 34% less (percent relative bias) for males and females, respectively. Therefore, our observed apparent survival rates of 0.52 and 0.39 for male and female warblers, respectively, may represent true survival rates of 0.69 and 0.60. Differential emigration rates confound inferences regarding differences in apparent survival between sexes and among species. Moreover, the bias introduced by using apparent survival rates for true survival rates can have profound effects on the predictions of population persistence through time, source/sink dynamics, and other aspects of life-history theory. For instance, we demonstrate with a stochastic population persistence model that if apparent survival rate estimates are used as true survival estimates, the underestimate of true survival because of emigration results in the misclassification of a local "source" population as a "sink". We investigated two study designs and analysis approaches that may result in apparent survival estimates that are closer to true survival estimates. The first involved a smaller "core" area where all marking of birds takes place and progressively larger "resighting" areas surrounding the core where researchers search for marked birds. We demonstrate that as the resighting areas get progressively larger, and therefore incorporate more "emigrants," apparent survival estimates begin to approximate true survival rates. Second, we investigated using a Robust Design data collection and analysis approach to estimate emigration rates directly. Both approaches are limited by logistical difficulties of data collection, but provide less biased estimates of survival.