Abstract Logistic regression has become increasingly popular for modeling nest success in terms of nest-specific explanatory variables. However, logistic regression models for nest fate are inappropriate when applied to data from nests found at various ages, for the same reason that the apparent estimator of nest success is biased (i.e. older clutches are more likely to be successful than younger clutches). A generalized linear model is presented and illustrated that gives ornithologists access to a flexible, suitable alternative to logistic regression that is appropriate when exposure periods vary, as they usually do. Unlike the Mayfield method (1961, 1975) and the logistic regression method of Aebischer (1999), the logistic-exposure model requires no assumptions about when nest losses occur. Nest survival models involving continuous and categorical explanatory variables, multiway classifications, and time-specific (e.g. nest age) and random effects are easily implemented with the logistic-exposure model. Application of the model to a sample of Yellow-breasted Chat (Icteria virens) nests shows that logistic-exposure estimates for individual levels of categorical explanatory variables agree closely with estimates obtained with Johnson (1979) constant-survival estimator. Use of the logistic-exposure method to model time-specific effects of nest age and date on survival of Blue-winged Teal (Anas discors) and Mallard (A. platyrhynchos) nests gives results comparable to those reported by Klett and Johnson (1982). However, the logistic-exposure approach is less subjective and much easier to implement than Klett and Johnson's method. In addition, logistic-exposure survival rate estimates are constrained to the (0,1) interval, whereas Klett and Johnson estimates are not. When applied to a sample of Mountain Plover (Charadrius montanus) nests, the logistic-exposure method gives results either identical to, or similar to, those obtained with the nest survival model in program MARK (White and Burnham 1999). I illustrate how the combination of generalized linear models and information-theoretic techniques for model selection, along with commonly available statistical software, provides ornithologists with a powerful, easily used approach to analyzing nest success.

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Blackbirds rearing five broods in one season. Br. Birds 55:189-190.

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The Food Security Act of 1985 contained provisions that affected wildlife conservation nationwide. Two provisions that most benefited waterfowl populations in the Prairie Pothole Region (PPR) were the Conservation Reserve Program (CRP) and “Swampbuster” (wetland conservation). Permanent cover established under the CRP provides attractive nesting habitat for upland‐nesting ducks that is more secure than other major habitats. Swampbuster has prevented drainage of wetlands vital to breeding duck pairs. In 2007 many CRP contracts will expire. Deliberations will begin in late 2006 regarding the next Farm Bill. The United States Department of Agriculture needs sound biological information and scientific analyses to help establish wildlife priorities in the Farm Bill. We used data from breeding duck population and wetland habitat surveys to develop models for 5 species of upland‐nesting ducks and applied these models to >2.6 million wetlands in a digital database for the PPR in North and South Dakota, USA. We used geographic information systems techniques to identify locations in the PPR where CRP cover would be accessible to the greatest number of nesting hens. We then summarized distribution of current CRP contracts relative to distribution of upland‐breeding ducks. We also used our models to predict change in the breeding duck population (landscape carrying capacity) that might occur if certain wetlands were exempt from the Swampbuster provision. Our analyses showed that 75% of CRP contracts as of July 2005 were in areas accessible to high or medium numbers of breeding ducks and 25% were in areas of low populations. We suggest a method to prioritize CRP extensions and reenrollment of current contracts or target new contracts to maintain or increase duck production. Additionally, our models suggested that if the Swampbuster provision were removed from future Farm Bills and protected wetland were drained, this area of the PPR could experience a 37% decline in the waterfowl populations we studied.

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