Geology topics

G. Loery

Publications and source records attributed to G. Loery.

3 recordsLinked to original sources

USGS1997

Capture-recapture analysis of a wintering black-capped chickadee population in Connecticut, 1958-1993

We investigated the dynamics of a wintering population of Black-capped Chickadees ( Parus atricapillus ) using data from a long-term capture-recapture study. Goodness-of-fit and likelihood-ratio tests indicated that the standard Jolly-Seber model was inadequate for the data, so we explored different parameterizations of a model in which survival probability for new captures differed from that of previously marked birds. One possible explanation for the lower local survival rate of new captures is that some of the birds were transients that had no chance of being recaptured. Average survival probability over the entire period was 0.62, and the estimated fraction of transients among unmarked birds was 0.27. We found evidence that chickadee survival rates were lower in years immediately following establishment of the Tufted Titmouse ( Parus bicolor ) as a territorial species (after 1967) than during years immediately preceding this event. We found no evidence that chickadee survival rates were lower in the years immediately following establishment of territorial raptors (after 1984) than during preceding years. Evidence suggested a long-term decline in survival probability from 1959 to 1991.

The Auk↗

USGS1987

Age-specificity of black-capped chickadee survival rates: Analysis of capture-recapture data

The ornithological literature indicates a widespread belief in two generalizations about the age—specificity of avian survival rates: (1) survival rates of young birds for some period following fledging are lower than those of adults, and (2) after reaching adulthood survival rates are constant for birds of all ages. There is a growing body of evidence in support of the first generalization, although little is known about how long the survival difference between young and adults lasts. This latter question can be addressed with capture—recapture or band recovery studies based on birds marked in the winter, but the inability to determine age in many species during winter has prevented the use of standard methods. There is very little evidence supporting the second generalization, and we are in need of methods and actual analyses that address this question. In the present paper we restate the two generalizations as hypotheses and test them using data from a wintering Black—capped Chickadee (Parus atricapillus) population in Connecticut, which has been studied by Loery for 26 yr. We use a cohort—based Jolly—Seber approach, which should be useful in other investigations of this nature. We found strong evidence of lower survival rates in 1st—yr birds than in adults, but could not determine whether this was the result of higher mortality rates, higher emigration rates, or a combination of the two. We also found evidence that survival rates of adult birds were not constant with age but decreased at a rate of ° 3.5%/yr. As adult birds are very faithful to their wintering areas, we believe that almost all this decrease can be attributed to an increase in mortality with age. Simulation results suggest that heterogeneity of capture probabilities could not explain the magnitude of the decrease in survival with age. Age—dependent tag loss is also discussed as an alternative explanation, but is dismissed as very unlikely in this situation. This analysis thus provides some of the first evidence of declining adult survival probabilities with age for any bird species.

Ecology↗

USGS1985

Dynamics of a black-capped chickadee population, 1958-1983

The dynamics of a wintering population of Black—capped Chickadees (Parus atricapillus) were studied from 1958—1983 using capture—recapture methods. The Jolly—Seber model was used to obtain annual estimates of population size, survival rate, and recruitment. The average estimated population size over this period was °160 birds. The average estimated number of new birds entering the population each year and alive at the time of sampling was °57. The arithmetic mean annual survival rate estimate was °0.59. We tested hypothesis about possible relationships between these population parameters and (1) the natural introduction of Tufted Titmice (Parus bicolor) to the area, (2) the clear—cutting of portions of nearby red pine (Pinus resinosa) plantations, and (3) natural variations in winter temperatures. The chickadee population exhibited a substantial short—term decline following titmouse establishment, produced by decreases in both survival rate and number of new recruits. Survival rate decline somewhat after the initiation of the pine clear—cutting, but population size was very similar before and after clear—cutting. Weighted least squares analyses provided no evidence of a relationship between survival rate and either of two winter temperature variables.

Ecology↗