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Geology topics

James D. Nichols

Publications and source records attributed to James D. Nichols.

154 records · Page 9Linked to original sources
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↗
USGS1984

The use of a robust capture-recapture design in small mammal population studies: A field example with Microtus pennsylvanicus

The robust design of Pollock (1982) was used to estimate parameters of a Maryland M. pennsylvanicus population. Closed model tests provided strong evidence of heterogeneity of capture probability, and model M eta (Otis et al., 1978) was selected as the most appropriate model for estimating population size. The Jolly-Seber model goodness-of-fit test indicated rejection of the model for this data set, and the M eta estimates of population size were all higher than the Jolly-Seber estimates. Both of these results are consistent with the evidence of heterogeneous capture probabilities. The authors thus used M eta estimates of population size, Jolly-Seber estimates of survival rate, and estimates of birth-immigration based on a combination of the population size and survival rate estimates. Advantages of the robust design estimates for certain inference procedures are discussed, and the design is recommended for future small mammal capture-recapture studies directed at estimation.

Acta Theriologica↗
USGS1984

Optimal timing in biological processes

A general approach for obtaining solutions to a class of biological optimization problems is provided. The general problem is one of determining the appropriate time to take some action, when the action can be taken only once during some finite time frame. The approach can also be extended to cover a number of other problems involving animal choice (e.g., mate selection, habitat selection). Returns (assumed to index fitness) are treated as random variables with time-specific distributions, and can be either observable or unobservable at the time action is taken. In the case of unobservable returns, the organism is assumed to base decisions on some ancillary variable that is associated with returns. Optimal policies are derived for both situations and their properties are discussed. Various extensions are also considered, including objective functions based on functions of returns other than the mean, nonmonotonic relationships between the observable variable and returns; possible death of the organism before action is taken; and discounting of future returns. A general feature of the optimal solutions for many of these problems is that an organism should be very selective (i.e., should act only when returns or expected returns are relatively high) at the beginning of the time frame and should become less and less selective as time progresses. An example of the application of optimal timing to a problem involving the timing of bird migration is discussed, and a number of other examples for which the approach is applicable are described.

American Naturalist↗
USGS1983

Factors affecting the distribution of mallards wintering in the Mississippi Alluvial Valley

The Mississippi Alluvial Valley (MAV) is the principal wintering area for Mallards ( Anas platyrhynchos ) in the Mississippi Flyway. Here, we consider it a distinct habitat ( sensu Fretwell 1972), i.e. fitness is relatively homogeneous among ducks within the MAV but different from that of ducks in other such habitats. We analyzed recovery distributions of Mallards banded preseason (July-September 1950-1980) to test hypotheses concerning the effects of winter temperatures, precipitation, and population levels on Mallard winter distribution. When two groups of years that comprised extremes of warm and cold winter weather were compared, recovery distributions of all four age and sex classes (adult males and females, young males and females) differed significantly; recoveries were located farther south in cold years. Recovery distributions also differed between wet and dry years in the MAV for all groups except adult males, higher proportions of recoveries of adult females and of young males and females occurring in the MAV during wet winters. Although differences in continental Mallard population size were associated with differences in recovery distributions only of adult males and young females, the proportion of young males and of all young Mallards recovered in the MAV increased during years of low populations. We conclude that temperature, water conditions, and population size affect the habitat suitability of Mallard wintering areas and that Mallards exhibit considerable flexibility in winter distribution associated with these factors.

Mississippi Alluvial Valley↗
USGS1983

The relationship between harvest and survival rates of mallards: A straightforward approach with partitioned data sets

We randomly partitioned mallard ( Anas platyrhynchos ) bandings and recoveries from each of a number of selected reference areas into 2 groups and estimated survival and harvest rates for each area and group. This procedure produced independent vectors of survival- and harvest-rate estimates, which were used to test the general hypothesis that mallard survival and harvest rates were inversely related. We used Spearman rank correlation analysis and z-test contrasts between survival rates from years of high vs. low harvest rates. We also conducted computer simulation experiments to gain insight into the ability of these analyses to detect the relationship of interest. The data analyses suggested that survival and harvest rates of young females were inversely related, at least for the 5 areas included in the analysis. However, for young males and adults of both sexes, the analyses provided no evidence of an inverse relationship between survival and harvest rates, except possibly in a few specific areas.

Journal of Wildlife Management↗
USGS1982

Additional comments on the assumption of homogeneous survival rates in modern bird banding estimation models

We examined the problem of heterogeneous survival and recovery rates in bird banding estimation models. We suggest that positively correlated subgroup survival and recovery probabilities may result from winter banding operations and that this situation will produce positively biased survival rate estimates. The magnitude of the survival estimate bias depends on the proportion of the population in each subgroup. Power of the suggested goodness-of-fit test to reject the inappropriate model for heterogeneous data sets was low for all situations examined and was poorest for positively related subgroup survival and recovery rates. Despite the magnitude of some of the biases reported and the relative inability to detect heterogeneity, we suggest that levels of heterogeneity normally encountered in real data sets will produce relatively small biases of average survival rates.

Journal of Wildlife Management↗
USGS1982

Breeding-ground habitat conditions and the survival of mallards

The relationship between habitat conditions in prairie breeding areas of North America and mallard ( Anas platyrhynchos ) survival rates was investigated. Annual survival-rate estimates for mallards generally were higher during years of high May pond numbers and low mallards-per-pond ratios than during years of low pond numbers and high ratios. This tendency was most pronounced among males. These results suggest that mallard survival probabilities may be affected by breeding-ground habitat conditions.

Journal of Wildlife Management↗
USGS1980

On the variability of alligator sex ratios

Samples of alligators from wild and 'farm' populations exhibited disproportionate sex ratios. Males predominated among young alligators from wild populations, whereas females were much more abundant than males in the farm population, where resources were superabundant. These results and other considerations lead us to hypothesize that environmental factors influence sex determination in alligators. During favorable environmental conditions natural selection is expected to favor a preponderance of the sex whose individuals exhibit the greater environmentally associated variation in relative fitness. We hypothesize that environmentally associated variation in age at sexual maturity of females produces sufficient variation in relative fitness of females to result in selection for low sex ratios during periods of resource abundance.

American Naturalist↗