8:55-9:15 AM Examining competing hypotheses for mechanisms of Cassin's Auklet population trajectory - Nadav Nur, Derek Lee & Bill Sydeman Cassins Auklet (Ptycoramphus aleuticus) numbers are considered to be at their lowest point in history throughout their range, and breeding populations are currently in decline at Triangle Island, British Columbia, and Southeast Farallon Island (SEFI), California, the only large colonies with long term data available. Using data from 21 years of mark-recapture, breeding performance, diet, chick growth rates, and oceanographic conditions at a Cassin's Auklet colony on SEFI, we examined interannual and decadal scales of variation in the population's vital rates and how they can explain population trends for this isolated population. Thanks to the depth and breadth of our data on this population, we were able to examine variation on multiple time scales, and with the aim of uncovering processes at work within this population, both ultimate factors (e.g., related to climate change and physical forcing of the marine environment) and proximal factors (reflected in indices of prey availability, indices of predation, and variation in chick growth rates). 9:15-9:35 AM Constrained influence of cyclic environmental variability on population dynamics of Antarctic predators. - Stephanie Jenouvrier, Cristophe Barbraud, Bernard Cazelles & Henri Weimerskirch Ecological and population processes are affected by climatic fluctuations, and top predators such as seabirds can provide an integrative view on the consequences of environmental variability on ecosystems. Over the Southern Ocean cyclic fluctuations of physical environment such as pression, sea surface temperature or sea ice are linked to large scale climatic oscillations like the southern oscillation. White and Peterson (1996) described also an Antarctic Circumpolar Wave (ACW) that propagates eastward coupled warm anomalies of sea surface temperature and sea ice extent with a period of 4-5 years. In this study we examine the cyclic dynamics of several seabirds population (southern fulmar, emperor penguin and snow petrel) in Antarctica, to evaluate the impact of environmental variability on the demographic parameters and to model the dynamics of populations. Population dynamics of southern fulmar, emperor penguin and snow petrel show cyclic fluctuations with a period of 2-4 years. By using wavelet analysis we pointed out that southern fulmar showed a period of 2-4 years after the eighties, whereas snow petrel and emperor penguins showed a similar period before the eighties. A regime shift occurred during the eighties and appear to synchronise the populations of these 3 species, which were not synchronised during the greater part of the forty years study. Long term monitoring of marked individuals of the 3 species enabled us to estimate demographics parameters such as breeding success or survival with capture-recapture analysis. We studied the influence of several environmental parameters (sea surface temperature, sea ice) on these life history traits and showed that species have constrated responses to climatic variations. For example, the survival rate of emperor penguins and southern fulmars increases when sea ice extent increases, while the survival rate of snow petrels decreases. Using these long- term series on demographic parameters together with their relationships with climatic factors, we model the population dynamics with Leslie matrices integrating the cyclicity in the variation of the demographics parameters. These modelled population trajectories were then compared with the observed cyclicity in the population size surveys. 9:35-9:55 AM Estimating the effects of fluctuating prey on demographic parameters of tawny owls - Charles Francis & Pertti Saurola Breeding populations and demographic parameters of many species of owls have been shown to vary in response to fluctuating prey populations. For example, breeding success and emigration patterns of several European owl species fluctuate in response to the 3-4 year cycle of many rodents (Saurola 1997), while breeding propensity, clutch size, nesting success, movement patterns and survival rates of Great Horned Owls vary in relation to the ~10-year cycle in Snowshoe Hare abundance (Houston & Francis 1995). However, little is known of the relative importance of these different factors on the population dynamics of owls. Since 1974, over 30,000 individuals of both young and breeding adult Tawny Owls have been ringed in Finland, generating over 9,000 live recaptures and dead recoveries. In addition, many territories are monitored each year, providing information on breeding propensity, clutch size, and nesting success. We used mark-recapture-recovery models to estimate variation in survival rates in relation to lemming cycles, as well as the severity of winter weather. By combining recapture and recovery data, we can estimate the relative importance of emigration and mortality on variation in apparent survival rates. We then use these estimates, together with productivity and nesting propensity data in a stage-based matrix model, to determine the relative influence of variation in these different demographic parameters on variation in population size of the species. Finally, we compare the model predictions with direct estimates of changes in population size derived from censuses and mark-recapture analyses. 9:55-10:15 AM Population models in greater snow geese: a comparison of different approaches - Gilles Gauthier & Jean-Dominique Lebreton Population model is a powerful tool to guide decision making when managing wildlife populations. We will compare different modeling approaches that we used to evaluate the effect of increased harvest on the population growth of Greater Snow Geese. For this population, we benefit of two unique datasets. On one hand, fecundity and survival data come from a long-term capture-recapture study conducted since 1990 at the breeding colony of Bylot Island in the Canadian Arctic. On the other hand, accurate estimates of the total size of the population come from an annual spring photo inventory conducted since 1970 in southern Quebec. Harvest data can be obtained from the national hunter surveys. In a first approach, we included environmental stochasticity in a matrix projection model by simulating good, average and bad years to account for the large inter-annual variation in fecundity and first-year survival, a common feature of birds nesting in the Arctic. However, caution must be used with this approach because different stochastic growth rates can be obtained according to the model formulation used (post-breeding vs pre-breeding census) when covariance among matrix elements is present, as this was the case here. A second approach that we developed is based on the functional relationships between generation time and elasticity on one hand, and harvest rate and survival on the other hand. Generation time was obtained from the mean transition matrix based on the observed proportion of good, average and bad years between 1985-98. The model assumes that hunting mortality is additive to natural mortality, for which we have good evidence. This yielded a simple formula that can predict changes in lambda as a function of changes in harvest. A third, and potentially more robust approach, consists in combining different sources of information in the same model, that is demographic data (i.e. transition matrix) and census data (i.e. annual survey). The Kalman Filter is a technique that precisely allows that. The advantage of this approach is that it attempts to minimize both uncertainties associated with the survey and demographic parameters based on the variance of each estimate. We will use the case of the greater snow goose to illustrate this newest approach. 10:15-10:35 AM A Bayesian Approach to Combining Animal Abundance and Demographic Data - Steven Brooks, Ruth King & Byron Morgan In studies of wild animals, one frequently encounters both census and mark-recapture recovery data. In this talk we consider a Bayesian analysis of joint ring-recovery and census data using a state-space model allowing for the fact that not all members of the population are directly observable. We then impose a Leslie-matrix-based model on the true population counts describing the natural birth-death and age transition processes. We use Markov chain Monte Carlo (MCMC) methods to perform the analysis, removing the need to use the Kalman filter and thereby allowing us to avoid the need for the potentially restrictive normality assumptions commonly assumed for analyses of this sort. We illustrate our approach on two important British bird species, the lapwing and the heron. In both cases, we introduce additional time-varying covariates such as the number of frost days each year in order to better explain the annual variability in the population. We use reversible jump MCMC to discriminate between alternative models describing the underlying population dynamics.