Combining Site Occupancy, Breeding Population Sizes and Reproductive Success to Calculate Time-Averaged Reproductive Output of Different Habitat Types: An Application to Tricolored Blackbirds
نویسندگان
چکیده
In metapopulations in which habitat patches vary in quality and occupancy it can be complicated to calculate the net time-averaged contribution to reproduction of particular populations. Surprisingly, few indices have been proposed for this purpose. We combined occupancy, abundance, frequency of occurrence, and reproductive success to determine the net value of different sites through time and applied this method to a bird of conservation concern. The Tricolored Blackbird (Agelaius tricolor) has experienced large population declines, is the most colonial songbird in North America, is largely confined to California, and breeds itinerantly in multiple habitat types. It has had chronically low reproductive success in recent years. Although young produced per nest have previously been compared across habitats, no study has simultaneously considered site occupancy and reproductive success. Combining occupancy, abundance, frequency of occurrence, reproductive success and nest failure rate we found that that large colonies in grain fields fail frequently because of nest destruction due to harvest prior to fledging. Consequently, net time-averaged reproductive output is low compared to colonies in non-native Himalayan blackberry or thistles, and native stinging nettles. Cattail marshes have intermediate reproductive output, but their reproductive output might be improved by active management. Harvest of grain-field colonies necessitates either promoting delay of harvest or creating alternative, more secure nesting habitats. Stinging nettle and marsh colonies offer the main potential sources for restoration or native habitat creation. From 2005-2011 breeding site occupancy declined 3x faster than new breeding colonies were formed, indicating a rapid decline in occupancy. Total abundance showed a similar decline. Causes of variation in the value for reproduction of nesting substrates and factors behind continuing population declines merit urgent investigation. The method we employ should be useful in other metapopulation studies for calculating time-averaged reproductive output for different sites.
منابع مشابه
Factors influencing territorial occupancy and reproductive success in a Eurasian Eagle-owl (Bubo bubo) population
Modelling territorial occupancy and reproductive success is a key issue for better understanding the population dynamics of territorial species. This study aimed to investigate these ecological processes in a Eurasian Eagle-owl (Bubo bubo) population in south-eastern Spain during a seven-year period. A multi-season, multi-state modelling approach was followed to estimate the probabilities of oc...
متن کاملPhysical habitat quality and interspecific competition interact to influence territory settlement and reproductive success in a cavity nesting bird
*Correspondence: John A. Jones, Biology Department, Appalachian State University, 572 Rivers Street, Boone, NC 28608-2027, USA e-mail: [email protected] Determining how to best measure habitat quality is essential for many conservation plans and basic ecological questions. Territory quality is thought to be a product of physical habitat characteristics (i.e., habitat quality) and the densit...
متن کاملChroniC low reproduCtive suCCess oF the Colonial triColored blaCkbird From 2006 to 2011
I studied the tricolored Blackbird (Agelaius tricolor) in California’s Central Valley over six breeding seasons from 2006 through 2011 and documented fates of nesting attempts, reproductive success of colonies, and relative abundance of insect prey in foraging areas. I found widespread and chronic reproductive failures except in cases of relatively high insect abundance. My observations suggest...
متن کاملUnderstanding the contribution of habitats and regional variation to long-term population trends in tricolored blackbirds
Population trends represent a minimum amount of information required to assess the conservation status of a species. However, understanding and detecting trends can be complicated by variation among habitats and regions, and by dispersal connecting habitats through source-sink dynamics. We analyzed trends in breeding populations between habitats and regions to better understand the overall dyna...
متن کاملTerritory Occupancy and Parental Quality as Proxies for Spatial Prioritization of Conservation Areas
In order to maximize their fitness, individuals aim at choosing territories offering the most appropriate combination of resources. As population size fluctuates in time, the frequency of breeding territory occupancy reflects territory quality. We investigated the relationships between the frequency of territory occupancy (2002-2009) vs. habitat characteristics, prey abundance, reproductive suc...
متن کامل