During 1983-1985, we studied the reproductive success of several species of aquatic birds (coots, ducks, shorebirds, and grebes) nesting at two sites in Merced County, California: a selenium-contaminated site (Kesterson Reservoir) and a nearby reference site (Volta Wildlife Area). We used a computer program (MICROMORT) developed for the analysis of radiotelemetry data (Heisey and Fuller 1985) to estimate nest success and causespecific failure rates, and then compared these parameters and hatchability between sites and among years.Nest success and causes of failure varied by species, site, and year. The most important causes of nest failure were usually predation, desertion, and water-level changes. However, embryotoxicosis (mortality, deformity, and lack of embryonic development) was the most important cause of nest failure in Eared Grebes (Podiceps nigricollis) at Kesterson Reservoir. Embryotoxicosis also reduced the hatchability of eggs of all other species at Kesterson in one or more years; embryonic mortality occurred rarely at Volta, and abnormalities were not observed.

Lake and stream habitats pose a variety of challenges to fishes due to differences in variables such as water velocity, habitat structure, prey community, and predator community. These differences can cause divergent selection on body size and/or shape. Here, we measured sex, age, length, and eight different morphological traits of the blackstripe topminnow, Fundulus notatus, from 19 lake and stream populations across four river drainages in central Illinois. Our goal was to determine whether size and shape differed consistently between lake and stream habitats across drainages. We also considered the effects of age and sex as they may affect size and morphology. We found large differences in body size of age 1 topminnows where stream fish were generally larger than lake fish. Body shape mainly varied as a function of sex. Adult male topminnows had larger morphological traits (with the exception of body width) than females, in particular longer dorsal and anal base lengths. Subtle effects of habitat were present. Stream fish had a longer dorsal fin base than lake fish. These phenotypic patterns may be the result of genetic and/or environmental variation. As these lakes are human-made, the observed differences, if genetic, would have had to occur relatively rapidly (within about 100 years).

Many animals exhibit alternative forms of reproductive behavior, the expression of which depends on individual condition or status. For instance, male smallmouth bass Micropterus dolomieu that are large early in life often build a nest and spawn for the first time at a young age and small body size, while males that are small early in life delay reproduction, invest in growth and spawn when they are older and larger, tactics referred to as α and β, respectively. The observation that larger males also tend to spawn earlier within a season led to a hypothesis that birthdate – more specifically, dispersal date – may control which tactic is adopted. Here, we examined the individual growth and reproductive histories of 184 male M. dolomieu of three cohorts for evidence of a birthdate effect on early life condition and the subsequent expression of tactics, namely whether a long first‐year growth period tends to induce the α tactic and whether variability in the timing of reproduction by parents within a season contributes to body size differences in progeny at the end of their first‐year growth period. The extent to which male condition early in life influences the expression of tactics was also evaluated. Evidence of a birthdate effect on progeny condition and subsequent tactic choice was observed for only one of the three cohorts and, in another cohort, tactic choice and individual condition were largely unrelated. The seasonal variability in birthdates and growth histories suggest that a broad range of swim‐up dates may be necessary to generate differences in condition early in life that are sufficiently large to control future reproductive decisions. Potential impacts of various physical, environmental and biotic factors that may mediate the seasonal timing of reproduction by parents or individual growth early in life are discussed.

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