Ecological and spatial drivers of population synchrony in bird assemblages

Spatial population synchrony is defined as the coincidental changes of population density or other demographic parameters over time. Synchrony between local populations is believed to be widespread in nature because it has been found across a range of ecological guilds and across large spatial scales. However, a detailed understanding is still lacking of the extent of synchronous patterns in population parameters across animal communities, and of the relative importance of the several potential causes of population synchrony. This study aimed to contribute to the understanding of how widespread spatial synchrony is in bird communities and to identify the main ecological drivers of synchrony. To achieve this we examined patterns of synchrony among bird populations inhabiting two contrasting areas of southeast Australia: the Victoria Central Highlands and Booderee National Park. Bird populations were studied through yearly point counts spanning 2004-2012 in Victoria and 2003-2012 in Booderee National Park. Our empirical assessment showed that spatial proximity, synchrony in weather (cumulative rainfall) and habitat type influenced the level of spatial synchrony in 11 out of the 38 species examined (i.e. 29% of the species). Synchrony was primarily driven by spatial proximity, followed by synchrony in rainfall; habitat similarity played a small role as driver of synchrony in both areas.