Dataset Information

Competition and habitat quality influence age and sex distribution in wintering rusty blackbirds.

ABSTRACT: Bird habitat quality is often inferred from species abundance measures during the breeding and non-breeding season and used for conservation management decisions. However, during the non-breeding season age and sex classes often occupy different habitats which suggest a need for more habitat-specific data. Rusty Blackbird (Euphagus carolinus) is a forested wetland specialist wintering in bottomland hardwood forests in the south-eastern U. S. and belongs to the most steeply declining songbirds in the U.S. Little information is available to support priority birds such as the Rusty Blackbird wintering in this threatened habitat. We assessed age and sex distribution and body condition of Rusty Blackbirds among the three major habitats used by this species in the Lower Mississippi Alluvial Valley and also measured food availability. Overall, pecan groves had the highest biomass mainly driven by the amount of nuts. Invertebrate biomass was highest in forests but contributed only a small percentage to overall biomass. Age and sex classes were unevenly distributed among habitats with adult males primarily occupying pecan groves containing the highest nut biomass, females being found in forests which had the lowest nut biomass and young males primarily staying in forest fragments along creeks which had intermediate nut biomass. Males were in better body condition than females and were in slightly better condition in pecan groves. The results suggest that adult males occupy the highest quality habitat and may competitively exclude the other age and sex classes.

SUBMITTER: Mettke-Hofmann C

PROVIDER: S-EPMC4422684 | biostudies-literature | 2015

REPOSITORIES: biostudies-literature

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Competition and habitat quality influence age and sex distribution in wintering rusty blackbirds.

Mettke-Hofmann Claudia C Hamel Paul B PB Hofmann Gerhard G Zenzal Theodore J TJ Pellegrini Anne A Malpass Jennifer J Garfinkel Megan M Schiff Nathan N Greenberg Russell R

PloS one 20150506 5

Bird habitat quality is often inferred from species abundance measures during the breeding and non-breeding season and used for conservation management decisions. However, during the non-breeding season age and sex classes often occupy different habitats which suggest a need for more habitat-specific data. Rusty Blackbird (Euphagus carolinus) is a forested wetland specialist wintering in bottomland hardwood forests in the south-eastern U. S. and belongs to the most steeply declining songbirds in ...[more]

PMID: 25946335

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Project description:BACKGROUND: Natural communities are structured by intra-guild competition, predation or parasitism and the abiotic environment. We studied the relative importance of these factors in two host-social parasite ecosystems in three ant communities in Europe (Bavaria) and North America (New York, West Virginia). We tested how these factors affect colony demography, life-history and the spatial pattern of colonies, using a large sample size of more than 1000 colonies. The strength of competition was measured by the distance to the nearest competitor. Distance to the closest social parasite colony was used as a measure of parasitism risk. Nest sites (i.e., sticks or acorns) are limited in these forest ecosystems and we therefore included nest site quality as an abiotic factor in the analysis. In contrast to previous studies based on local densities, we focus here on the positioning and spatial patterns and we use models to compare our predictions to random expectations. RESULTS: Colony demography was universally affected by the size of the nest site with larger and more productive colonies residing in larger nest sites of higher quality. Distance to the nearest competitor negatively influenced host demography and brood production in the Bavarian community, pointing to an important role of competition, while social parasitism was less influential in this community. The New York community was characterized by the highest habitat variability, and productive colonies were clustered in sites of higher quality. Colonies were clumped on finer spatial scales, when we considered only the nearest neighbors, but more regularly distributed on coarser scales. The analysis of spatial positioning within plots often produced different results compared to those based on colony densities. For example, while host and slavemaker densities are often positively correlated, slavemakers do not nest closer to potential host colonies than expected by random. CONCLUSIONS: The three communities are differently affected by biotic and abiotic factors. Some of the differences can be attributed to habitat differences and some to differences between the two slavemaking-host ecosystems. The strong effect of competition in the Bavarian community points to the scarcity of resources in this uniform habitat compared to the other more diverse sites. The decrease in colony aggregation with scale indicates fine-scale resource hotspots: colonies are locally aggregated in small groups. Our study demonstrates that species relationships vary across scales and spatial patterns can provide important insights into species interactions. These results could not have been obtained with analyses based on local densities alone. Previous studies focused on social parasitism and its effect on host colonies. The broader approach taken here, considering several possible factors affecting colony demography and not testing each one in isolation, shows that competition and environmental variability can have a similar strong impact on demography and life-history of hosts. We conclude that the effects of parasites or predators should be studied in parallel to other ecological influences.

Project description:Knowledge about the population size and trends of common bird species is crucial for setting conservation priorities and management actions. Multi-species large-scale monitoring schemes have often provided such estimates relying on extrapolation of relative abundances in particular habitats to large-scale areas. Here we show an alternative to inference-rich predictive models, proposing methods to deal with caveats of population size estimations in habitat-specialist species, reed warblers (Acrocephalus scirpaceus and Acrocephalus arundinaceus). Reed warblers were only found in pure reedbeds within riparian woodlands or in riparian vegetation scattered within or around reedbed patches, as expected according to their habitat specialization. The proportion of individuals located in reedbed associated with lotic and lentic waters differed between species, and no reed warbler was recorded in reedbed located along dry streams. This indicates that microhabitat features or their effects on reedbed structure and other factors made a proportion of the apparently available habitat unsuitable for both warbler species. Most warblers detected were males performing territorial singing (females seldom sing and do not perform elaborate territorial song, and are undistinguishable from males by plumage). The regional population sizes of the warbler species (~4000 individuals of A. scirpaceus and ~ 1000 individuals of A. arundinaceus) were much smaller than those estimated for the same area by transforming relative abundance obtained at a national scale to population size through extrapolation by habitat at a regional scale. These results highlight the importance of considering the habitat actually used and its suitability, the manner of sex-related detection, population sex-ratio and their interactions in population estimates. Ideally, the value of predictive methods to estimate population size of common species should be tested before conducting large-scale monitoring, rather than a posteriori. Although logistically challenging, this can be achieved by designing monitoring programs including an intensive sampling of abundance in ad hoc reference areas of variable size.

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Dataset Information

Competition and habitat quality influence age and sex distribution in wintering rusty blackbirds.

Publications

Competition and habitat quality influence age and sex distribution in wintering rusty blackbirds.

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