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Mortality estimation based on carcass searches

We are working intensively on the development of methods for the estimation of mortality based on carcass searches since 2008. The main question we deal with is how many animals have actually been killed given a specific number of carcasses were found while taking into account that not all carcasses are in the searched area, that carcasses can be removed by scavengers and that the searcher may overlook some carcasses. We solve these questions using probablity calculations where the theorem of Bayes plays an important role. We participate in an international expert group that aims at developing the software "Generalized Fatality Estimator". More than 20 publications and the R-package "carcass" have resulted from our work. The latest publication reviews the statistical principles of mortality estimation based on carcass searches:

Huso M, Dalthorp D, Korner-Nievergelt F (2017) Statistical Principles of Post-Construction Fatality Monitoring Design. In Perrow M (ed) Wildlife and Wind Farms, Conflicts and Solutions, Volume 2, Onshore: Monitoring and Mitigation. Pelagic Publishing, Exeter. link to book












 

Estimating adult sex ratio in birds using mist nets data
Research Station Petite Camargue Alsacienne

Skewed adult sex ratio may play an important role in ecology, evolution and conservation of animals. In birds, published estimateds on adult sex ratios mostly rely on mist netting data. However, previous studies suggested that mist nets or other trap types provide biased estimates on sex ratios, with males being more susceptible to capture than females.

We used data from a Constant Effort Site ringing scheme to show how sex ratios that are corrected for sex- and year-specific capture probabilities can be directly estimated by applying capture-recapture analysis, for example, in a Bayesian framework.

When capture data were pooled from the 19 years of study, we found that in the blackbird (Turdus merula) and the blackcap (Sylvia atricapilla), the observed proportions of males were 57% and 55%, respectively. However, when the observed annual proportions of males were corrected for the sex-specific capture probabilities, the proportions of males did not clearly differ from 50% in most study years, and thus, the apparent male-bias in the adult sex ratios almost completely disappeared.

We propose that published estimates on adult sex ratios in birds should be re-evaluated if based solely on observed sex ratios from mist netting studies. We further propose that data from national bird ringing schemes and in particular from Constant Effort Site ringing programs can provide valuable information on adult sex ratios, if analysed using capture-recapture models. We discuss important assumptions of those models; for example, movements that may differ between sexes should be taken into account, as well as the occurrence of transient individuals that do not hold breeing territories within a study site.

Amrhein et al. (2012) Estimating adult sex ratios from bird mist netting data. Methods in Ecology and Evolution 3:713-720. doi: 10.1111/j.2041-210X.2012.00207.x



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