USGS Science⌕ Search

Geology topics

H. Hafner

Publications and source records attributed to H. Hafner.

4 recordsLinked to original sources
USGS2004

Do adult Little Egrets respond to disturbance at their nest by increased breeding dispersal?

When studying breeding dispersal with marked individuals, manipulation-induced disturbance should not affect movement patterns. As part of a study on the Little Egret ( Egretta garzetta ), we tested whether the capture of breeding adults at their nest and handling (i.e., disturbance) increased their probability to move to a new colony in the subsequent breeding season (i.e., breeding dispersal). The proportion of adults disturbed in a given year that had changed colony in the subsequent breeding season was compared with the dispersal of adults observed during at least two consecutive years at colonies and not disturbed on the previous year: (1) birds marked as chicks and (2) birds marked as adults and observed ≥ two years after capture at the nest . Disturbed birds were not found to have an increased propensity to disperse. We conclude that, for this species, capture did not increase the subsequent breeding dispersal.

Camargue↗
USGS2003

Estimating rates of local extinction and colonization in colonial species and an extension to the metapopulation and community levels

Coloniality has mainly been studied from an evolutionary perspective, but relatively few studies have developed methods for modelling colony dynamics. Changes in number of colonies over time provide a useful tool for predicting and evaluating the responses of colonial species to management and to environmental disturbance. Probabilistic Markov process models have been recently used to estimate colony site dynamics using presence–absence data when all colonies are detected in sampling efforts. Here, we define and develop two general approaches for the modelling and analysis of colony dynamics for sampling situations in which all colonies are, and are not, detected. For both approaches, we develop a general probabilistic model for the data and then constrain model parameters based on various hypotheses about colony dynamics. We use Akaike's Information Criterion (AIC) to assess the adequacy of the constrained models. The models are parameterised with conditional probabilities of local colony site extinction and colonization. Presence–absence data arising from Pollock's robust capture–recapture design provide the basis for obtaining unbiased estimates of extinction, colonization, and detection probabilities when not all colonies are detected. This second approach should be particularly useful in situations where detection probabilities are heterogeneous among colony sites. The general methodology is illustrated using presence–absence data on two species of herons. Estimates of the extinction and colonization rates showed interspecific differences and strong temporal and spatial variations. We were also able to test specific predictions about colony dynamics based on ideas about habitat change and metapopulation dynamics. We recommend estimators based on probabilistic modelling for future work on colony dynamics. We also believe that this methodological framework has wide application to problems in animal ecology concerning metapopulation and community dynamics.

Oikos↗
USGS2000

Introduction

Explore the source record for details and available documents.

Book chapter↗