WATERFOWL POPULATION STATUS, 1999

This report summarizes the most recent information on the status of North American duck populations to facilitate development of harvest regulations in the U.S. The results in this report differ from those published in the earlier •Trends in Duck Breeding Populations, 1955-99. Because of recent changes, tables from the Trend Report, not normally included in the Status Report, will be included this year. The 1999 estimate for total ducks in the traditional survey area was 43.4 million birds, the largest population size estimated since operational surveys began in 1955. This is an increase (P\u3c0.01) of 11% over that of 1998, and 32% higher (P\u3c0.01) than the 1955-98 average. Mallard (Anas platyrhynchos) abundance was 10.8 million, the second largest population size estimated. This is an increase of 12% (P=0.01) over last year and 47% (P\u3c0.01) greater than the long-term average. Blue-winged teal (Anas discors) abundance was 7.1 million, an all-time high, and 65% greater than the long-term average (P\u3c0.01). Northern pintail (Anas acuta), scaup (Aythya marila and Aythya affinis), green-winged teal (Anas crecca), and northern shoveler (Anas clypeata) numbers increased from 1998 estimates, while gadwall (Anas strepera) decreased (P\u3c0.04). Gadwall, green-winged teal, northern shoveler, redheads (Aythya americana), and canvasbacks (Aythya valisineria) were above their respective long-term averages (P\u3c0.05), while pintails and scaup remained below their long-term averages (P\u3c0.01). American wigeon (Anas americana) numbers were unchanged from last year or from long-term average. May habitat conditions in the traditional survey area were generally good to excellent, except for a few dry areas primarily in southern and central Alberta, Montana, and central Saskatchewan. The number of May ponds in the traditional survey area was 6.7 million, an increase of 46% over 1998 and 37% above the long-term average (P\u3c0.01). In the eastern areas of Canada and the U.S. (strata 51-56 and 62), the total number of ducks (1.2 million) remained unchanged from last year and the 1995-98 average (P\u3c0.10). Numbers of individual species in the east were similar to those of last year (P • 0.10), except for goldeneye (Bucephala clangula and B. islandica), which were 196% greater than 1998 levels, and scaup, which were 93% below 1998 levels. Goldeneye were above their 1995-98 average, while blue-winged teal and scaup were below (P\u3c0.03). Habitats in the east were somewhat drier than last year, and conditions were overall not as favorable for waterfowl production. The estimate of the total-duck fall-flight index is105 million birds, compared to 84 million last year. The fall flight is predicted to include 13.6 million mallards, 16% greater (P\u3c0.01) than the estimate of 11.8 million in 1998

Disease dynamics in wild populations: modeling and estimation: a review

Abstract Models of infectious disease dynamics focus on describing the temporal and spatial variations in disease prevalence, and on understanding the factors that affect how many cases will occur in each time period and which individuals are likely to become infected. Classical methods for selecting and fitting models, mostly motivated by human diseases, are almost always based solely on raw counts of infected and uninfected individuals. We begin by reviewing the main classical approaches to parameter estimation, and some of their applications. We then review recently developed methods which enable representation of component processes such as infection and recovery, with observation models that acknowledge the complexities of the sampling and detection processes. We demonstrate the need to account for detectability in modeling disease dynamics, and explore a number of mark-recapture and occupancy study designs for estimating disease parameters while simultaneously accounting for variation in detectability. We highlight the utility of different modeling approaches and also consider the typically strong assumptions that may actually serve to limit their utility in general application to the study of disease dynamics (e.g., assignment of individuals to discrete disease states when underlying state space is more generally continuous; transitions assumed to be simple firstorder Markov; temporal separation of hazard and transition events)

Looking for a needle in a haystack: inference about individual fitness components in a heterogeneous population

Studies of wild vertebrates have provided evidence of substantial differences in lifetime reproduction among individuals and the sequences of life history ‘states’ during life (breeding, nonbreeding, etc.). Such differences may reflect ‘fixed’ differences in fitness components among individuals determined before, or at the onset of reproductive life. Many retrospective life history studies have translated this idea by assuming a ‘latent’ unobserved heterogeneity resulting in a fixed hierarchy among individuals in fitness components. Alternatively, fixed differences among individuals are not necessarily needed to account for observed levels of individual heterogeneity in life histories. Individuals with identical fitness traits may stochastically experience different outcomes for breeding and survival through life that lead to a diversity of ‘state’ sequences with some individuals living longer and being more productive than others, by chance alone. The question is whether individuals differ in their underlying fitness components in ways that cannot be explained by observable ‘states’ such as age, previous breeding success, etc. Here, we compare statistical models that represent these opposing hypotheses, and mixtures of them, using data from kittiwakes. We constructed models that accounted for observed covariates, individual random effects (unobserved heterogeneity), first-order Markovian transitions between observed states, or combinations of these features. We show that individual sequences of states are better accounted for by models incorporating unobserved heterogeneity than by models including first-order Markov processes alone, or a combination of both. If we had not considered individual heterogeneity, models including Markovian transitions would have been the best performing ones. We also show that inference about age-related changes in fitness components is sensitive to incorporation of underlying individual heterogeneity in models. Our approach provides insight into the sources of individual heterogeneity in life histories, and can be applied to other data sets to examine the ubiquity of our results across the tree of life

Fledging size and survival in snow geese: Timing is everything (or is it?)

In many birds, body size at fledging is assumed to predict accurately the probability of subsequent survival, and size at fledging is often used as a proxy variable in analyses attempting to assess the pattern of natural selection on body size. However, in some species, size at fledging can vary significantly as a function of variation in the environmental component of growth. Such developmental plasticity has been demonstrated in several species of Arctic-breeding geese. In many cases, slower growth and reduced size at fledging has been suggested as the most parsimonious explanation for reduced post-fledging survival in goslings reared under poor environmental conditions. However, simply quantifying a relationship between mean size at fledging and mean survival rate (Francis et al ., 1992) may obscure the pattern of selection on the interaction of the genetic and environmental components of growth. The hypothesis that selection operates on the environmental component of body size at fledging, rather than the genetic component of size per se, was tested using data from the long-term study of Lesser Snow Geese ( Anser c. caerulescens ) breeding at La Perouse Bay, Manitoba, Canada. Using data from female goslings measured at fledging, post-fledging survival rates were estimated using combined live encounter and dead recovery data (Burnham, 1993). To control for the covariation between growth and environmental factors, survival rates were constrained to be functions of individual covariation of size at fledging, and various measures of the timing of hatch; in all Arctic-breeding geese studied to date, late hatching goslings grow significantly more slowly than do early hatching goslings. The slower growth of late-hatching goslings has been demonstrated to reflect systematic changes in the environmental component of growth, and thus controlling for hatch date controls for a significant proportion of variation in the environmental component of growth. The relationship between size at fledging, hatch date and survival was found to be significantly non-linear; among early hatching goslings, there was little indication of significant differences in survival rate among large and small goslings. However, with increasingly later hatch dates, there was progressively greater mortality selection against smaller, slower growing goslings in most years. This would appear to suggest that body size matters, but not absolutely; small size leads to reduced survival for late-hatching goslings only at La Perouse Bay. Since at least some of the variation in size among goslings for a given hatch date reflects genetic differences, this suggests selection may favour larger size at fledging, albeit only among late-hatching goslings.

Waterfowl Population Status, 2000

In the traditional survey area (strata 1-18, 20-50, and 75-77), total duck abundance was 41.8 ± 0.7 million birds. This was similar (P=0.12) to last year’s record high estimate of 43.4 ± 0.7 million birds, and 27% above the long-term (i.e., 1955-99) average (P\u3c0.01). Mallard (Anas platyrhynchos) abundance was 9.5 ± 0.3 million, which is 12% below (P\u3c0.01) the 1999 estimate of 10.8 ± 0.3 million and 27% above the long-term average (P\u3c0.01). Blue-winged (Anas discors) and green-winged teal (Anas crecca) abundances were both at record high levels this spring. Blue-winged teal abundance was 7.4 ± 0.4 million, which was similar to last year’s estimate of 7.1 ± 0.4 million (P=0.61) and 69% above the long-term average (P\u3c0.01). Green-winged teal abundance was 3.2 ± 0.2 million, 80% above the long-term average (P\u3c0.04) and 21% higher than last year (P=0.03). Gadwall (Anas strepera; 3.2 ± 0.2 million, +100%), northern shovelers (Anas clypeata; 3.5 ± 0.2 million, +73%), and redheads (Aythya americana; 0.9 ± 0.1 million, +50%) were all above their long-term averages (P\u3c0.01), while northern pintails (Anas acuta; 2.9± 0.2 million, -33%) and scaup (Aythya marila and A. affinis combined; 4.0 ± 0.2 million, -25%) remained below their long-term averages (P\u3c0.01). American wigeon (Anas americana) and canvasback (Aythya valisineria) estimates were similar to those of last year (P≥0.42) and to long-term averages (P\u3e0.07). May conditions in the traditional survey area were generally drier than last year. The estimate of May ponds in Prairie Canada and the U.S. combined was 3.9 ± 0.1 million, down 41% from 1999 and 20% below the long-term average (P\u3c0.01). The eastern survey area comprises strata 51-56 and 62-69. The 2000 total duck population estimate for the eastern survey area was 3.2 ± 0.3 million birds. This was essentially identical to last year’s total duck estimate of 3.2 ± 0.2 million birds. Abundances of individual species were similar to last year, with the exception of scoters (Melanitta spp.; 182 ± 59 thousand, +288%, P=0.03) and green-winged teal (202 ± 29 thousand, -52%, P\u3c0.01)). The total duck fall flight index for 2000 is 90 million birds. This is 13 percent lower than last year’s record fall flight. Because of additions to the survey area for which we do not have production information, we propose to stop calculating the traditional fall-flight index for total ducks in the future. The Service may consider other alternatives to provide a reflection of duck abundance in the fall. The midcontinent mallard fall flight is predicted to be 11.3 million mallards, 16.2% lower than that of last year (P\u3c0.01)

Transient animals in a resident population of snow geese: Local emigration or heterogeneity?

International audienceThe estimation of survival rates from analysis of recapture of individually marked animals assumes that all individuals are equally likely to be re-encountered. This assumption is frequently violated in natural populations due to movements to and from the sampling area. W e evaluated potential sources of heterogeneity using data from recaptures of 36000 individually marked female lesser snow geese, Anser c. caerules-cens, from an expanding population in northern M anitoba, Canada. By stratifying individuals according to marking age and origin (hatched at the colony or not), we assessed the degree to which variation in apparent survival re¯ected permanent or temporary differences in emigration and effects of handling. In general, for birds ringed as adults, estimated apparent survival rates were signi® cantly lower during the ® rst year after ringing than in subsequent years. By comparing birds ringed as adults (classi® ed by origin) with those ringed as goslings, we were able to demonstrate that these differences are not due to permanent emigration from the colony by transient individuals or heterogeneity of individual capture probability, but more likely re¯ect differences among individuals in their response to initial marking. Approximately 25% of birds permanently emigrate from the sampling area following marking

Model-based estimation of individual fitness

Fitness is the currency of natural selection, a measure of the propagation rate of genotypes into future generations. Its various definitions have the common feature that they are functions of survival and fertility rates. At the individual level, the operative level for natural selection, these rates must be understood as latent features, genetically determined propensities existing at birth. This conception of rates requires that individual fitness be defined and estimated by consideration of the individual in a modelled relation to a group of similar individuals; the only alternative is to consider a sample of size one, unless a clone of identical individuals is available. We present hierarchical models describing individual heterogeneity in survival and fertility rates and allowing for associations between these rates at the individual level. We apply these models to an analysis of life histories of Kittiwakes ( Rissa tridactyla ) observed at several colonies on the Brittany coast of France. We compare Bayesian estimation of the population distribution of individual fitness with estimation based on treating individual life histories in isolation, as samples of size one (e.g. McGraw & Caswell, 1996).

Occam's shadow: Levels of analysis in evolutionary ecology--where to next?

Evolutionary ecology is the study of evolutionary processes, and the ecological conditions that influence them. A fundamental paradigm underlying the study of evolution is natural selection. Although there are a variety of operational definitions for natural selection in the literature, perhaps the most general one is that which characterizes selection as the process whereby heritable variation in fitness associated with variation in one or more phenotypic traits leads to intergenerational change in the frequency distribution of those traits. The past 20 years have witnessed a marked increase in the precision and reliability of our ability to estimate one or more components of fitness and characterize natural selection in wild populations, owing particularly to significant advances in methods for analysis of data from marked individuals. In this paper, we focus on several issues that we believe are important considerations for the application and development of these methods in the context of addressing questions in evolutionary ecology. First, our traditional approach to estimation often rests upon analysis of aggregates of individuals, which in the wild may reflect increasingly non-random (selected) samples with respect to the trait(s) of interest. In some cases, analysis at the aggregate level, rather than the individual level, may obscure important patterns. While there are a growing number of analytical tools available to estimate parameters at the individual level, and which can cope (to varying degrees) with progressive selection of the sample, the advent of new methods does not reduce the need to consider carefully the appropriate level of analysis in the first place. Estimation should be motivated a priori by strong theoretical analysis. Doing so provides clear guidance, in terms of both (i) assisting in the identification of realistic and meaningful models to include in the candidate model set, and (ii) providing the appropriate context under which the results are interpreted. Second, while it is true that selection (as defined) operates at the level of the individual, the selection gradient is often (if not generally) conditional on the abundance of the population. As such, it may be important to consider estimating transition rates conditional on both the parameter values of the other individuals in the population (or at least their distribution), and population abundance. This will undoubtedly pose a considerable challenge, for both single- and multi-strata applications. It will also require renewed consideration of the estimation of abundance, especially for open populations. Thirdly, selection typically operates on dynamic, individually varying traits. Such estimation may require characterizing fitness in terms of individual plasticity in one or more state variables, constituting analysis of the norms of reaction of individuals to variable environments. This can be quite complex, especially for traits that are under facultative control. Recent work has indicated that the pattern of selection on such traits is conditional on the relative rates of movement among and frequency of spatially heterogeneous habitats, suggesting analyses of evolution of life histories in open populations can be misleading in some cases.