Multistate Capture-recapture Models Research Articles

The magnitude and selectivity of natural and multiple anthropogenic mortality causes in hunted brown bears

1. The population dynamic and evolutionary effects of harvesting are receiving growing attention among biologists. Cause-specific estimates of mortality are necessary to determine and compare the magnitude and selectivity of hunting and other types of mortalities. In addition to the logistic and financial constraints on longitudinal studies, they are complicated by the fact that nonhunting mortality in managed populations usually consists of a mix of natural and human-caused factors. 2. We used multistate capture-recapture (MCR) models to estimate cause-specific survival of brown bears (Ursus arctos) in two subpopulations in Sweden over a 23-year period. In our analysis, we distinguished between legal hunting and other sources of mortality, such as intraspecific predation, accidents, poaching, and damage control removals. We also tested whether a strong increase in harvest quotas after 1997 in one of the subpopulations affected vulnerability to legal hunting. 3. Although only a fraction of mortalities other than legal hunting could be considered natural, this group of causes showed a general pattern of demographic selectivity expected from natural mortality regimes in populations of long-lived species, namely greater vulnerability of young animals. On the other hand, demographic effects on hunting vulnerability were weak and inconsistent. Our findings support the assumption that hunting and other mortalities were additive. 4. As expected, an increase in hunting pressure coincided with a correspondingly large increase in vulnerability to hunting in the affected subpopulation. Because even unbiased harvest can lead to selective pressures on life-history traits, such as size at primiparity, increasing harvest quotas may not only affect population growth directly, but could also alter optimal life-history strategies in brown bears and other carnivores. 5. Legal hunting is the most conveniently assessed and the most easily managed cause of mortality in many wild populations of large mammals. Although legal hunting is the single-most important cause of mortality for brown bears in Sweden, the combined mortality from other causes is of considerable magnitude and additionally shows greater selectivity in terms of sex and age than legal hunting. Therefore, its role in population dynamics and evolution should not be underestimated.

Estimating survival and movements using both live and dead recoveries: a case study of oystercatchers confronted with habitat change

Summary Animals facing partial habitat loss can try to survive in the remaining habitat or emigrate. Effects on survival and movements should be studied simultaneously since survival rates may be underestimated if emigrants are not considered, and since emigrants may experience reduced survival. We analysed movements and survival of adult wintering oystercatcher Haematopus ostralegus in response to the 1986–1987 partial closure of the Oosterschelde in the Dutch Delta. This reduced by one‐third the tidal area of this major European wintering area for waders. We developed a novel variant of a multistate capture–recapture model allowing simultaneous estimation of survival and movement between sites using a mixture of data (live recaptures and dead recoveries). We used a two‐step process, first estimating movements between sites followed by site‐specific survival rates. Most birds were faithful to their ringing site. Winter survival was negatively affected by winter severity and was lowest among birds changing wintering site (i.e. moving outside of the Oosterschelde). During mild winters, survival rates were very high, and similar to before the closure in both changed and unchanged sectors of the Oosterschelde. However, the combined effect of habitat loss with severe winters decreased the survival of birds from changed sectors and induced emigration. The coastal engineering project coincided with three severe winters and high food stock, making assessment of its effects difficult. However, the habitat loss seems to have had less impact on adult survival and movements than did winter severity. Synthesis and applications. Human‐induced habitat change may result in population decline through costly emigration or reduced survival or reproduction of individuals that stay. Long‐term monitoring of marked individuals helps to understand how populations respond to environmental change, but site‐specific survival and movement rates should be integrated in the same model in order to maximize the information yield. Our modelling approach facilitates this because it allows the inclusion of recoveries from outside the study area.

AGE-SPECIFIC SURVIVAL, BREEDING SUCCESS, AND RECRUITMENT IN COMMON MURRES (URIA AALGE) OF THE CALIFORNIA CURRENT SYSTEM

Abstract Estimating age-specific vital rates and determining which of them have the greatest influence on population trajectory is very useful for conservation and management of at-risk species. We created multistate capture–recapture models to provide estimates of age-specific variation in survival, recruitment, breeding propensity, and breeding success of Common Murres (Uria aalge) breeding at Southeast Farallon Island, California. Model-averaged age functions indicated that a plateauing (inverse age) function best characterized recruitment probability (transition from nonbreeder to breeder state) and breeding success (fledglings per pair). Adult and juvenile survival and breeding propensity were best modeled as constant with age. We modeled the population using an extended Leslie matrix and determined elasticity values for each of our estimated parameters to determine which have the greatest influence on population growth. Elasticities indicated that variation in adult survival had the greatest influ...

How do different releasing techniques affect the survival of reintroduced grey partridges Perdix perdix?

Abstract The quality of released individuals can have a significant impact on the success of reintroduction projects. We tested which of the following release techniques resulted in the highest survival of released grey partridges Perdix perdix in Switzerland : 1) translocation of wild adult birds, 2) release of captive parent-reared adults as family groups, and 3) fostering of captive parent-reared chicks to wild barren pairs. Wild hatched offspring (F1 birds) from our re-established breeding pairs served as the control group. We used a multi-state capture-recapture model to estimate monthly survival rates from the data based on monitoring of radio-tagged individuals and reobservation and recovery of ringed individuals. Survival tended to be highest in wild-hatched partridges of the founder population (mean±SE; 0.90±0.03), followed by that of fostered chicks (0.86±0.03) and translocated adult wild birds (0.82±0.06). While survival of these groups was not statistically different from each other, survival ...

Population dynamics in a long‐lived seabird: I. Impact of breeding activity on survival and breeding probability in unbanded king penguins

Understanding the trade-off between current reproductive effort, future survival and future breeding attempts is crucial for demographic analyses and life history studies. We investigated this trade-off in a population of king penguins (Aptenodytes patagonicus) marked individually with transponders using multistate capture-recapture models. This colonial seabird species has a low annual proportion of non-breeders (13%), despite a breeding cycle which lasts over 1 year. To draw inferences about the consequences of non-breeding, we tested for an effect of reproductive activity on survival and on the probability of subsequent breeding. We found that birds non-breeding in year t show the same survival rate as breeders (two-states analysis: breeding and non-breeding). However, breeders had a lower probability of breeding again the following year. This negative phenotypic correlation suggests the existence of reproductive costs affecting future breeding probability, but it might also be strengthened by late arrival for courtship in year t. A three-state analysis including breeding success revealed that failed breeders in year t have a lower probability to reproduce successfully in year t + 1 than non-breeders in year t, providing some evidence for the existence of reproductive costs. Moreover, successful breeders showed higher survival probability. This positive phenotypic correlation between current reproduction and subsequent survival supports the hypothesis of an heterogeneity in individual quality. Males breeding in year t had a lower probability to breed again in year t + 1 than females, suggesting higher reproductive costs for this sex. Such additional costs might be due to higher male parental investment in the final phase of chick-rearing, which also delays the arrival of males in year t + 1, and decreases their breeding probability. Our study is the first to explore the breeding biology and the demography of penguins without the disturbance of flipper-bands.

Are extra‐pair young better than within‐pair young? A comparison of survival and dominance in alpine marmot

1. In socially monogamous species, females may seek extra-pair copulation to gain genetic benefits. In order to test this 'genetic quality' hypothesis, one must compare the performance of extra-pair young (EPY) and within-pair young (WPY). Such tests, however, are scarce and results published so far are inconclusive. 2. Here, we test the 'genetic quality' hypothesis using multistate capture-recapture models to compare age-specific survival and access to dominance between EPY and WPY in the alpine marmot Marmota marmota, a socially monogamous mammal showing extra-pair paternities. 3. When compared with WPY, survival of EPY was higher by 15%, 10% and 30%, for juveniles, yearlings and 2-year-old individuals, respectively. Survival at older ages did not differ. 4. Survival corresponded to true survival for yearlings and juveniles as dispersal does not occur before 2 years of age in marmots. For older individuals, survival estimates included a mixture of survival and dispersal. The 30% increase of the 2-year-old EPY survival might reflect delayed dispersal rather than high survival of EPY as compared with WPY. 5. WPY and EPY had the same probability (0.28) to access dominance at 2 years of age, but EPY were more successful at older ages than WPY (0.46 vs. 0.10). 6. Both survival and reproductive performance were higher in EPY than in WPY. The fitness advantages of adopting such a mixed mating tactic are thus likely to be high for marmot females. We suggest that obtaining genetic benefits is the main evolutionary force driving extra-pair paternity in alpine marmots.

Age‐specific survival and reproductive performances in fur seals: evidence of senescence and individual quality

Life history theory hypothesises that breeding events induce reproductive costs that may vary among individuals. However, the growing number of studies addressing this question are taxonomically biased, therefore impeding the generalisation of this hypothesis, especially with regard to marine top predators. This study investigated age‐related survival and breeding performances in subantarctic fur seal (Arctocephalus tropicalis) females from Amsterdam Island, southern Indian Ocean. Using multistate capture–recapture models on data obtained from known‐age tagged females over eight consecutive years, we tested for evidence of senescence, individual quality, and reproductive costs in terms of future survival and fecundity. Adult female yearly survival appeared high and constant throughout time. While a two age‐class model was preferred in non‐breeders, breeding females exhibited three age classes with a maximum survival for the prime‐age class (7–12 years). Survival and reproductive probabilities decreased from 13 years onward, suggesting senescence in this population. Survival was lower for non‐breeders than for breeders, among both prime‐aged (0.938 vs 0.982) and older (0.676 vs 0.855) females. Furthermore, non‐breeders exhibited higher probabilities of being non‐breeders the following year than did breeders (0.555 vs 0.414). Such results suggest consistency in female breeding performance over years, supporting the hypothesis that non‐breeding tend to occur among lower quality individuals rather than representing an alternative strategy to enhance residual reproductive value. However, the high proportion of females that did not breed during two consecutive years, and the lower probability of being a successful breeder after a greater reproductive effort confirmed the existence of reproductive costs, especially during the second half of the lactation. These results also suggest that younger age‐classes included a higher proportion of lower quality individuals, which are likely to face higher costs of reproduction. Such hypotheses lead to consider the first breeding event as a filter generating a within‐cohort selection process in females.

Principles and interest of GOF tests for multistate capture-recapture models

Optimal goodness–of–fit procedures for multistate models are new. Drawing a parallel with the corresponding single–state procedures, we present their singularities and show how the overall test can be decomposed into interpretable components. All theoretical developments are illustrated with an application to the now classical study of movements of Canada geese between wintering sites. Through this application, we exemplify how the interpretable components give insight into the data, leading eventually to the choice of an appropriate general model but also sometimes to the invalidation of the multistate models as a whole. The method for computing a corrective overdispersion factor is then mentioned. We also take the opportunity to try to demystify some statistical notions like that of Minimal Sufficient Statistics by introducing them intuitively. We conclude that these tests should be considered an important part of the analysis itself, contributing in ways that the parametric modelling cannot always do to the understanding of the data.

Comparison of size vs. life-state classification in demographic models for the terrestrial orchid Cleistes bifaria

Recent studies using capture–recapture modelling in terrestrial orchids have shown relationships among survival, life-state, climate and dormancy, but to date, there has been no rigorous study of the effects of size on demographic rates. Here we use multistate capture–recapture models to investigate the relationships between survival, ramet size, life-state, and propensity for extended dormancy of Cleistes bifaria in two populations in Florida and West Virginia. Using estimated leaf area as a measure of ramet size, we investigated relative fit to the data of models in which ramets were classified by life-state alone (dormant, vegetative, and flowering), size alone (dormant, small, and large), or by a combination of size and state (dormant, small vegetative, large vegetative, small flowering, and large flowering ramets). This scheme allowed us to compare the effects of a size versus state classification on survival and transition probabilities, including the propensity for dormancy. For survival rates, the size-classified model was preferable in terms of parsimony (AIC) to models classified either by state or by a combination of size and state. In C. bifaria, annual survival rate for large ramets was close to 1.0 and for small and dormant ramets, 0.91 and 0.76, respectively. This highlights the importance of protecting large plants. In contrast, a model combining life-state with ramet size was most parsimonious for explaining variation in transition rates. As the ‘size + state’ classification is convenient, holds more information, and seems more closely tied to fitness than classification by either size or life-state alone, it may be particularly useful in planning and assessing conservation management of orchids.

Multievent: An Extension of Multistate Capture–Recapture Models to Uncertain States

Capture-recapture models were originally developed to account for encounter probabilities that are less than 1 in free-ranging animal populations. Nowadays, these models can deal with the movement of animals between different locations and are also used to study transitions between different states. However, their use to estimate transitions between states does not account for uncertainty in state assignment. I present the extension of multievent models, which does incorporate this uncertainty. Multievent models belong to the family of hidden Markov models. I also show in this article that the memory model, in which the next state or location is influenced by the previous state occupied, can be fully treated within the framework of multievent models.

Colony Size Selection Determines Adult Survival and Dispersal Preferences: Allee Effects in a Colonial Bird

Avian coloniality traditionally has been investigated by examining how breeding success varies with colony size, but other crucial fitness components rarely have been examined. This may lead to wrong conclusions because unmeasured parameters may change the final fitness balance. We used multistate capture-recapture models to investigate adult survival and dispersal in relation to colony size within a long-term monitored population of lesser kestrels (Falco naumanni). Nest predation probability decreases with colony size, and adult survival is predicted to show the same trend because adults are exposed to the same suite of predators. As expected, survival probability was higher in large colonies (0.72+/-0.015; mean+/-SE) than in medium or small colonies (0.65+/-0.02). Additionally, dispersal probabilities were higher going from small to large colonies (0.20+/-0.01) than from large to small (0.08+/-0.01), as predicted by theory of habitat selection shaped by fitness maximization. These asymmetries are likely to generate size-specific colony population dynamics, so they should be taken into account in studies of colonial birds and other metapopulation-like systems. Allee effects, that is, positive density dependence, appear to be the cause of the evolution of dispersal behavior and may explain the maintenance of coloniality in this species.

Estimating predation on breeding European storm‐petrels ( Hydrobates pelagicus ) by yellow‐legged gulls ( Larus michahellis )

Several hypotheses about changes in adult survival of European storm-petrels Hydrobates pelagicus and predation by yellow-legged gulls Larus michahellis at Benidorm Island (western Mediterranean) during 1993–2003 were assessed. Two approaches were used: analysis of pellets containing remains of predated petrels from two caves, and multistate capture–recapture models using recaptures of breeders together with recoveries only from one of these caves. These models were used to estimate separately adult storm-petrel survival and a minimum probability of being killed by gulls. At least 11–14% of the storm-petrels killed had been ringed as breeders. Local adult survival varied greatly among years, from 0.701 (SE=0.095) to extremely high values (0.951, SE=0.031) for such a small species (0.833 on average for the whole period). Nevertheless, it was not possible to assess whether this variation was influenced by inter-annual differences in gull predation. The peak of predation occurred in June, when maximum numbers of prospecting petrels visit the colonies. Predation was much higher at the cave that received stronger illumination from Benidorm city. Minimum predation probabilities estimated from capture–recapture varied with time from 0.022 (SE=0.011) to 0.040 (SE=0.016), and increased significantly after the powering of light received from the city in 1997. In these years, predation by yellow-legged gulls accounted for a large percentage of mortality of storm-petrels at Benidorm Island (up to 33%). Both methodological approaches confirmed that predation was carried out by specialist gulls, and that neither the size of the gull colony nor its food availability influenced predation on petrels. Management might reduce predation rate by removing gulls that nest in the caves, since these individuals tend to kill most storm-petrels.

ENVIRONMENTAL CONDITIONS AND BREEDING EXPERIENCE AFFECT COSTS OF REPRODUCTION IN BLUE PETRELS

Using data from a 17-year study of individually marked Blue Petrels, we examined how survival and breeding probability varied with experience and breeding status, and looked for costs of first reproduction, taking into account environmental and individual variability. Using multistate capture–recapture models with four states (inexperienced nonbreeders, first-time breeders, experienced breeders, and experienced nonbreeders), we found that first-time breeders had a lower probability of surviving and breeding in the next year than experienced breeders. Survival of first-time breeders was lower than that of inexperienced nonbreeders, indicating a cost of first reproduction. Survival of inexperienced individuals (both breeders and nonbreeders), but not of experienced ones, was negatively affected by poor environmental oceanographic conditions. The costs of reproduction for first-time breeders were particularly marked during harsh weather conditions. Survival and the probability of breeding in the next year for experienced birds were higher for breeders than for nonbreeders. Similarly, the probability of breeding in the next year for first-time breeders was higher than for inexperienced nonbreeders. This suggests heterogeneity in quality among individuals. Experienced breeders had a higher body condition than first-time breeders and nonbreeders. Body condition did not affect the probability of surviving or breeding in the next year. These results can be interpreted in the light of a change in the proportion of individuals with different survival (selection hypothesis: low-quality individuals die sooner). The inferiority of first-time breeders may be linked to a higher proportion of lower-quality individuals in younger age classes. First reproduction may act as a filter, selecting individuals of higher quality. Sea surface height, reflecting food availability, is probably a key selective agent.

Predictors of reproductive cost in female Soay sheep

Summary We investigate factors influencing 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 investigate the influence of age and ecological conditions on the cost of reproduction, defined as the difference between survival of breeder and non‐breeder ewes on a logistic scale. The cost is identified as a quadratic function of age, being greatest for females breeding at 1 year of age and when more than 7 years old. Costs, however, were only present during severe environmental conditions (wet and stormy winters occurring when population density was high). Winter severity and population size explain most of the variation in the probability of breeding for the first time at 1 year of life, but did not affect the subsequent breeding probability. The presence of a cost of reproduction was confirmed by an experiment where a subset of females was prevented from breeding in their first year of life. Our results suggest that breeding decisions are quality or condition dependent. We show that the interaction between age and time has a significant effect on variation around the phenotypic trade‐off function: selection against weaker individuals born into cohorts that experience severe environmental conditions early in life can progressively eliminate low‐quality phenotypes from these cohorts, generating population‐level effects.

Demographic estimation methods for plants with unobservable life‐states

Demographic estimation of vital parameters in plants with an unobservable dormant state is complicated, because time of death is not known. Conventional methods assume that death occurs at a particular time after a plant has last been seen aboveground but the consequences of assuming a particular duration of dormancy have never been tested. Capture–recapture methods do not make assumptions about time of death; however, problems with parameter estimability have not yet been resolved. To date, a critical comparative assessment of these methods is lacking. We analysed data from a 10 year study of Cleistes bifaria, a terrestrial orchid with frequent dormancy, and compared demographic estimates obtained by five varieties of the conventional methods, and two capture–recapture methods. All conventional methods produced spurious unity survival estimates for some years or for some states, and estimates of demographic rates sensitive to the time of death assumption. In contrast, capture–recapture methods are more parsimonious in terms of assumptions, are based on well founded theory and did not produce spurious estimates. In Cleistes, dormant episodes lasted for 1–4 years (mean 1.4, SD 0.74). The capture–recapture models estimated ramet survival rate at 0.86 (SE∼0.01), ranging from 0.77–0.94 (SEs≤0.1) in any one year. The average fraction dormant was estimated at 30% (SE 1.5), ranging 16–47% (SEs≤5.1) in any one year. Multistate capture–recapture models showed that survival rates were positively related to precipitation in the current year, but transition rates were more strongly related to precipitation in the previous than in the current year, with more ramets going dormant following dry years. Not all capture–recapture models of interest have estimable parameters; for instance, without excavating plants in years when they do not appear aboveground, it is not possible to obtain independent time‐specific survival estimates for dormant plants. We introduce rigorous computer algebra methods to identify the parameters that are estimable in principle. As life‐states are a prominent feature in plant life cycles, multistate capture–recapture models are a natural framework for analysing population dynamics of plants with dormancy.

ESTIMATING SURVIVAL AND TEMPORARY EMIGRATION IN THE MULTISTATE CAPTURE–RECAPTURE FRAMEWORK

The open population Cormack-Jolly-Seber (CJS) capture–mark–recapture model for estimating survival allows for random temporary emigration from the sampling area, but Markovian temporary emigration can bias estimates of survival. We explore a multistate capture–recapture model that has been proposed for coping with Markovian temporary emigration. We provide a comprehensive assessment of the performance of this model using computer algebra and simulation. We found that most model parameters were identifiable unless survival, emigration, and immigration were all time dependent. Simulation results showed that intrinsically identifiable parameters were estimated without bias and that precision of survival estimates was always high. When temporary emigration was Markovian, precision of estimates of emigration, immigration, and recapture probabilities was acceptable; otherwise it was not. Test component 2.Ct of the goodness-of-fit test for the CJS model had good power to detect Markovian temporary emigration. We conclude that the multistate model works well when temporary emigration is Markovian (i.e., when the CJS model should not be used) and when survival and recapture probabilities are high.

Assessment of hypotheses about dispersal in a long‐lived seabird using multistate capture–recapture models

Summary Dispersal contributes to spatio‐temporal variation in population size and is a key process in studies of life history evolution and studies with conservation implications. However, dispersal is still one of the major gaps in our knowledge of ecological dynamics. The very large literature on metapopulation dynamics lacks empirical bases on dispersal and relevant behavioural parameters. We used multistate capture–recapture models (data from 1988 to 2001) to address hypotheses about movement probability and habitat selection within a system of two breeding colonies in Audouin's gulls (Larus audouinii), an endemic species breeding in the Mediterranean and considered as threatened. Movement probability varied over time, and differed greatly between the colonies. We did not find evidence of an influence of colony size or density of predators on movement probability. In dispersers, our results did not support the hypotheses that movement probability between year t and t+ 1 was influenced by mean breeding success in the colony of origin (i.e. an indicator of habitat quality) or the destination colony in year t or t+ 1, or by the ratio of breeding success in these colonies in year t or t + 1 (i.e. quality gradient). Overall, movement probability was higher from the smaller colony to the larger, and from the colony with lower breeding success in year t to the more productive one. This provides slight support for two nonexclusive hypotheses about habitat selection (conspecific attraction and conspecific success attraction). Movement probability from the smaller, less productive colony was very high in some years, suggesting that the dynamics of both colonies were strongly influenced by adult dispersal. However, in absolute numbers, more individuals moved from the larger, more productive colony to the smaller one. This suggests that the system may function as a source–sink system. Use of multistate models to re‐assess local survival showed that survival was lower in the less productive colony with higher emigration probability. This may reflect genuine differences in mortality between colonies, or more probably differences in permanent emigration from the study area.

M-SURGE: new software specifically designed for multistate capture-recapture models

M-SURGE (along with its companion program U-CARE) has been written specifically to handle multistate capture-recapture models and to alleviate their inherent difficulties (model specification, quality of convergence, flexibility of parameterization, assessment of fit). In its domain, M-SURGE covers a broader range of models than a general program like MARK (White & Burnham, 1999), while being more user-friendly than MS-SURVIV (Hines, 1994). Among the main features of M-SURGE is a wide class of models and a variety of parameterizations: (1) M-SURGE covers conditional models with probability of recapture depending on the current state (Arnason¿Schwarz type models) as well as on the current and previous state (Jolly-movement type models). In both cases, age and/or time-dependence and multiple groups can be considered. (2) Combined survival-transition probabilities can be represented as such or decomposed into transition and survival probabilities. (3) Among the transition probabilities with the same state of departure, the one to be computed by subtraction can be freely picked by the user. User-friendliness is enhanced by the easiness with which constrained models are built, using an interpreted language called GEMACO. Examples of various types of multistate models are developed and presented.

Testing the additive versus the compensatory hypothesis of mortality from ring recovery data using a random effects model

The interaction of an additional source of mortality with the underlying “natural” one strongly affects population dynamics. We propose an alternative way to test between two forms of interaction, total additivity and compensation. In contrast to existing approaches, only ring-recovery data where the cause of death of each recovered individual is known are needed. Cause-specific mortality proportions are estimated based on a multistate capture-recapture model. The hypotheses are tested by inspecting the correlation between the cause-specific mortality proportions. A variance decomposition is performed to obtain a proper estimate of the true process correlation. The estimation of the cause-specific mortality proportions is the most critical part of the approach. It works well if at least one of the two mortality rates varies across time and the two recovery rates are constant across time. We illustrate this methodology by a case study of White Storks Ciconia ciconia where we tested whether mortality induced by power line collision is additive to other forms of mortality.

Computing and software

The reality is that the statistical methods used for analysis of data depend upon the availability of software. Analysis of marked animal data is no different than the rest of the statistical field. The methods used for analysis are those that are available in reliable software packages. Thus, the critical importance of having reliable, up–to–date software available to biologists is obvious. Statisticians have continued to develop more robust models, ever expanding the suite of potential analysis methods available. But without software to implement these newer methods, they will languish in the abstract, and not be applied to the problems deserving them. In the Computers and Software Session, two new software packages are described, a comparison of implementation of methods for the estimation of nest survival is provided, and a more speculative paper about how the next generation of software might be structured is presented. Rotella et al. (2004) compare nest survival estimation with different software packages: SAS logistic regression, SAS non–linear mixed models, and Program MARK. Nests are assumed to be visited at various, possibly infrequent, intervals. All of the approaches described compute nest survival with the same likelihood, and require that the age of the nest is known to account for nests that eventually hatch. However, each approach offers advantages and disadvantages, explored by Rotella et al. (2004). Efford et al. (2004) present a new software package called DENSITY. The package computes population abundance and density from trapping arrays and other detection methods with a new and unique approach. DENSITY represents the first major addition to the analysis of trapping arrays in 20 years. Barker & White (2004) discuss how existing software such as Program MARK require that each new model’s likelihood must be programmed specifically for that model. They wishfully think that future software might allow the user to combine pieces of likelihood functions together to generate estimates. The idea is interesting, and maybe some bright young statistician can work out the specifics to implement the procedure. Choquet et al. (2004) describe MSURGE, a software package that implements the multistate capture–recapture models. The unique feature of MSURGE is that the design matrix is constructed with an interpreted language called GEMACO. Because MSURGE is limited to just multistate models, the special requirements of these likelihoods can be provided. The software and methods presented in these papers gives biologists and wildlife managers an expanding range of possibilities for data analysis. Although ease–of–use is generally getting better, it does not replace the need for understanding of the requirements and structure of the models being computed. The internet provides access to many free software packages as well as user–discussion groups to share knowledge and ideas. (A starting point for wildlife–related applications is (http://www.phidot.org).