Consequences of heterogeneity in survival probability in a population of Florida scrub-jays.

1. Using data on breeding birds from a 35-year study of Florida scrub-jays Aphelocoma coerulescens (Bosc 1795), we show that survival probabilities are structured by age, birth cohort, and maternal family, but not by sex. Using both accelerated failure time (AFT) and Cox proportional hazard models, the data are best described by models incorporating variation among birth cohorts and greater mortality hazard with increasing age. AFT models using Weibull distributions with the shape parameter > 1 were always the best-fitting models. 2. Shared frailty models allowing for family structure greatly reduce model deviance. The best-fitting models included a term for frailty shared by maternal families. 3. To ask how long a data set must be to reach qualitatively the same conclusions, we repeated the analyses for all possible truncated data sets of 2 years in length or greater. Length of the data set affects the parameter estimates, but not the qualitative conclusions. In all but three of 337 truncated data sets the best-fitting models pointed to same conclusions as the full data set. Shared frailty models appear to be quite robust. 4. The data are not adequate for testing hypotheses as to whether variation in frailty is heritable. 5. Substantial structured heterogeneity for survival exists in this population. Such structured heterogeneity has been shown to have substantial effects in reducing demographic stochasticity.

Metal and metalloid concentrations in the eggs of threatened Florida scrub-jays in suburban habitat from south-central Florida.

Monitoring and assessing changes in contaminants in urban and suburban environments is essential to assessing ecosystem well-being in human-influenced landscapes. We analyzed metal and metalloid levels in the eggs of the threatened Florida scrub-jay (Aphelocoma coerulescens), an extremely sedentary and modestly long-lived passerine bird that is federally threatened and endemic only in Florida. Eggs that failed to hatch were collected in a suburban environment to compare with the long-term study of this species at the Archbold Biological Station, located 8 km south in a more rural part of south-central Florida. Florida scrub-jays remain in a permanent territory in scrub oak habitat where they feed mainly on insects and acorns, but in suburban habitats human-provided foods comprise 30% of their diet. From the data previously collected at Archbold, and their low position on the food chain, we expected levels of contaminants to be comparatively low and remain relatively constant over time. Except for the low mercury value, all means were within the range of mean values reported for a wide range of non-passerine species (including those at higher tropic levels), are lower than concentrations associated with abnormalities in birds, and are lower than those previously reported for scrub-jays from Archbold Biological Station. A significant increase in selenium occurred from 1996 to 2001, but did not appear associated with changes in human density.

Arboviral infection in two species of wild jays (Aves: Corvidae): evidence for population impacts.

We examined the prevalence of antibodies to three mosquito-borne arboviruses in blue jays, Cyanocitta cristata, and Florida scrub-jays, Aphelocoma coerulescens, to identify the effects on host survival, the influence of sex and age on infection, and the temporal patterns of antibody prevalence. Blood samples from 306 blue jays and 219 Florida scrub-jays were collected at Archbold Biological Station (Lake Placid, FL) from April 1994 through December 1995. Sera were analyzed for hemagglutination-inhibition antibody to eastern equine encephalitis (EEE) and St. Louis encephalitis (SLE) viruses, and neutralizing antibodies to EEE, Highlands J (HJ), and SLE viruses. Overall, 31.4% of blue jay samples and 22.1% of scrub-jay samples had antibodies to EEE. Antibodies to HJ were detected in slightly >15% of samples in each jay species, and SLE was detected in <3% of the samples in each jay species. A single EEE virus isolation was made from the blood of an 11-d-old scrub-jay nestling. Survival of adult blue jays seropositive to EEE was significantly lower than that of seronegative birds based on resight rates, but infection did not seem to affect survival of adult or juvenile Florida scrub-jays.

THE EVOLUTION OF CLUTCH SIZE. II. A TEST OF THE MURRAY-NOLAN EQUATION.

We test the Murray-Nolan equation for calculating clutch sizes of birds with demographic data from a long-term study of the Florida Scrub Jay (Aphelocoma c. coerulescens). The predicted value, 3.43, is very close to the observed clutch size, 3.33. This result provides further support for the equation's being an adequate description of the relationship among the factors affecting the clutch size of birds.