Geology topics
Publications and source records attributed to J.D. Nichols.
The objectives of waterfowl management in North America involve population size and harvest. Any management action intended to influence population size must do so through one of four demographic variables: reproduction, mortality, immigration, and emigration. Mortality is especially important because hunting can be strongly influenced by management.
Our knowledge of the effects of hunting regulations on duck populations has been based largely on retrospective studies of historical data. We have reached the limits of what can be learned in this way. Future knowledge gains will likely come about only through experimentation and adaptive management.
Sample sizes necessary for estimating survival rates of banded birds, adults and young, are derived based on specified levels of precision. The banding study can be new or ongoing. The desired coefficient of variation (CV) for annual survival estimates, the CV for mean annual survival estimates, and the length of the study must be specified to compute sample sizes. A computer program is available for computation of the sample sizes, and a description of the input and output is provided.
To test the hypothesis that exposure to organophosphorus (OP) insecticides reduces postfledging survival of altricial birds, 16—d—old European Starlings ( Sturnus vulgaris ) were weighed and orally dosed with corn oil containing 6.0 mg of dicrotophos per kilogram of body mass or an equivalent exposure of pure corn oil (controls). Two days later, each survivor was weighed again and patagially tagged for identification after fledging. Resightings of marked fledglings were made during weekly 2—d intensive observations yielding four estimates of postfledging survival. Before fledging, only OP—dosed birds died (18.5%), and OP—dosed survivors lost more mass (5.2%, P = .001) than controls (1.4%) but their masses on day 18 were only slightly lower (2% of control mean, P = .10). Brain cholinesterase activity, a sensitive indicator of OP exposure in birds, was depressed and average of 93% in OP—dosed nestlings that died compared to controls, and an average of 46% in OP—dosed nestlings alive on day 18. Age at fledging, postfledging survival, flocking behavior, and habitat use, however, did not differ between OP—dosed and control birds. The effects of the OP on the nestlings appeared to be rapid, to be reversible in survivors, and did not extend into the postfledging period. In addition, we found no relationship between body mass at fledging and postfledging survival.
We outline a population model proposed to accommodate the full life cycle of the mallard (Anas platyrhynchos}. Events during the breeding season are better understood than events at other times of the year, but recent findings suggest the importance of phenomena away from the breeding grounds. Several processes are discussed relative to mallard population dynamics. Compensatory mortality is a poorly understood concept, but one that can overwhelm many other components of a population model. Diseases and environmental contaminants can inflict indirect as well as direct mortality and can reduce reproduction. They interact with numerous other variables in complex and yet unknown ways. Recent evidence of a wintering-ground effect on subsequent recruitment provides one avenue for modeling phenomena occurring at different times of the year. Finally, the role of heterogeneity among individuals is widely acknowledged but not fully appreciated. We illustrate with an example the importance of heterogenicity to population processes, including compensatory mortality.
Hand-reared canvasbacks (Aythya valisineria) of varying sex ratios were maintained in pens during winter 1980-81 (3M-3F, 6M-0F, 0M-6F) and winter 1981-82 (4M-2F, 2M-4F) and fed two diets (control and stress). They were observed during feeding trials to determine intrasexual and intersexual aggressive activity. There was little evidence that either diet or sex ratio affected the total number of aggressive encounters. Females fed both control and stress diets were more aggressive and spent more time in the small feeding areas than males in pens with 3M-3F, 4M-2F, and 2M-4F sex ratios. Stressed ducks tended to weigh less than controls throughout the study. Females in the 3M-3F and 4M-2F pens weighed less than those in the 0M-6F and 2M-4F pens, respectively. However, relative weight changes throughout the winter were similar for males and females. Thus, results of these experiments do not lead to conclusive rejection of either the behavioral dominance hypothesis or the fasting endurance hypothesis.
Explore the source record for details and available documents.
We outline a population model proposed to accommodate the full life cycle of the mallard (Anas platyrhynchos). Events during the breeding season are better understood than events at other times of the year, but recent findings suggest the importance of phenomena away from the breeding grounds. Several processes are discussed relative to mallard population dynamics. Compensatory mortality is a poorly understood concept, but one that can overwhelm many other components of a population model. Diseases and environmental contaminants can inflict indirect as well as direct mortality and can reduce reproduction. They interact with numerous other variables in complex and yet unknown ways. Recent evidence of a wintering-ground effect on subsequent recruitment provides one avenue for modeling phenomena occurring at different times of the year. Finally, the role of heterogeneity among individuals is widely acknowledged but not fully appreciated. We illustrate with an example the importance of heterogeneity to population processes, including compensatory mortality.
The usefulness of capture-recapture estimators in any field study will depend largely on underlying model assumptions and on how closely these assumptions approximate the actual field situation. Evaluation of estimator performance under real-world field conditions is often a difficult matter, although several approaches are possible. Perhaps the best approach involves use of the estimation method on a population with known parameters.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Mass and recapture histories of 6,000 Canvasbacks ( Aythya valisineria ) banded in upper Chesapeake Bay were used to test two hypotheses: (1) early-winter body mass is associated with the probability of surviving the winter, and (2) early-winter body mass is associated with annual survival probability. Data were analyzed by a binary regression method that treated mass as a continuous variable and estimated parameters to describe a general relationship between body mass and survival probability. Results for adult males, which provided our largest data sets, presented strong evidence that birds with high relative early-winter masses had both greater overwinter and annual survival probabilities. Results of overwinter analyses necessarily are qualified by the alternative explanation of mass-dependent emigration, i.e. the possibility that lighter birds move south in response to cold weather and leave only heavy birds for recapture. Such a phenomenon remains to be documented. Results concerning annual survival probabilities are not vulnerable to this alternative explanation because of the strong fidelity of Canvasbacks at the banding site. Because of small sample size, data were inadequate to permit mass/survival inferences for adult females. Sample sizes were adequate for young Canvasbacks, but the results were less consistent than for adult males. Although early-winter body mass was associated positively with overwinter as well as annual survival for young Canvasbacks in some years, we suspect that the lack of established wintering patterns among these birds may underlie the less consistent result.
The numbers of host-seeking adult American dog ticks, Dermacentor variabilis (Say), in a sweet gum field in Maryland reflected changes in the population density of a host species, the meadow vole, Microtus pennsylvanicus (Ord), which within 1.5 yr fell from an estimated 157 to 8 voles on a 0.8 ha grid. During high vole density, there was no significant difference ( P > 0.05) in tick burdens between sexes on an annual basis. Juvenile and subadult voles (< 33 g) harbored significantly fewer D. variabilis larvae and nymphs than did mature voles (> 33 g) on an annual basis. However, during periods of both peak host-seeking activity by D. variabilis larvae and nymphs and high host density nearly all the voles examined were infested. There was no evidence of a relationship between weight of adult voles and likelihood of parasitization by D. variabilis during months of moderate tick host-seeking activity. Of 163 adult D. variabilis recaptured ≥ one week after marking, 86 (52.7%) had moved > 3.8 m, 59 (36.2%) > 5.3 m.
No abstract available.
Jolly (1982, Biometrics 38, 301-321) presented modifications of the Jolly-Seber model for capture-recapture data, which assume constant survival and/or capture rates. Where appropriate, because of the reduced number of parameters, these models lead to more efficient estimators than the Jolly-Seber model. The tests to compare models given by Jolly do not make complete use of the data, and we present here the appropriate modifications, and also indicate how to carry out goodness-of-fit tests which utilize individual capture history information. We also describe analogous models for the case where young and adult animals are tagged. The availability of computer programs to perform the analysis is noted, and examples are given using output from these programs.
Explore the source record for details and available documents.