Understanding the contribution of habitats and regional variation to long-term population trends in tricolored blackbirds

July 23, 2013

This new study by Emilie Graves, Marcel Holyoak, and Bob Meese of U.C. Davis and Rodd Kelsey of The Nature Conservancy (formerly with Audubon California) analyzes over 100 years of colony occupation data to help to understand the contributions of breeding habitats and regional variation to population trends in tricolored blackbirds. Temporal trends differed between breeding habitat types and were associated with regional differences in population declines. A relatively new nesting substrate, triticale (a wheat x rye hybrid grain), has since the 1980's produced colonies 40× larger, on average, than other breeding habitats, and contributed to a change in regional distribution since it primarily occurred in the San Joaquin Valley. The mechanism for such an effect is not clear, but could represent the local availability of foodstuffs in the landscape (i.e. stored grains) rather than something specific to triticale crops. While variation in trends among habitats clearly occurred, they could not easily be ascribed to source-sink dynamics, ecological traps, habitat selection or other detailed ecological mechanisms.

It was published in the open access journal Ecology and Evolution.

ece3681.pdf2.75 MB