title: 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.
authors.affiliation: School of Natural Sciences and Psychology, Liverpool John Moores University, Liverpool, United Kingdom; Smithsonian Migratory Bird Center, National Zoological Park, Washington, D. C., United States of America.
authors.forename: Claudia
authors.initials: C
authors.lastname: Mettke-Hofmann
authors.affiliation: US Forest Service, Stoneville, MS, United States of America.
authors.forename: Paul B
authors.initials: PB
authors.lastname: Hamel
authors.affiliation: Tamar Grove, Moreton, United Kingdom.
authors.forename: Gerhard
authors.initials: G
authors.lastname: Hofmann
authors.affiliation: Department of Biological Sciences, University of Southern Mississippi, Hattiesburg, United States of America.
authors.forename: Theodore J
authors.initials: TJ
authors.lastname: Zenzal
authors.affiliation: SWCA Environmental Consultants, Flagstaff, AZ, United States of America.
authors.forename: Anne
authors.initials: A
authors.lastname: Pellegrini
authors.affiliation: School of Environment and Natural Resources, Ohio State University, Columbus OH, United States of America.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Malpass
authors.affiliation: Department of Wildlife, Humboldt State University, Arcata CA, United States of America.
authors.forename: Megan
authors.initials: M
authors.lastname: Garfinkel
authors.affiliation: US Forest Service, Stoneville, MS, United States of America.
authors.forename: Nathan
authors.initials: N
authors.lastname: Schiff
authors.affiliation: Smithsonian Migratory Bird Center, National Zoological Park, Washington, D. C., United States of America.
authors.forename: Russell
authors.initials: R
authors.lastname: Greenberg
mesh_terms: D000367:Age Factors; D063147:Animal Distribution; D000818:Animals; D018533:Biomass; D005260:Female; D020387:Food Chain; D065928:Forests; D008297:Male; D046109:Passeriformes / Q000254:growth & development / Q000502:physiology*; D012621:Seasons; D012737:Sex Factors