Drought Affects Dusky Orange-crowned Warbler
The winter of 2006-2007 was a brutal one in southern California. Little rain fell and the Channel Islands were particularly hard hit. The dusky orange-crowned warbler, a subspecies of the orange-crowned warbler that only nests on Catalina and Santa Cruz islands, was particularly impacted.
On Catalina Island breeding commenced 2 months late and only 5 (out of 45) females built nests. Of these, only 1 laid eggs and those young eventually starved.
Santa Cruz Island had a little more winter rainfall than Catalina so more females nested and laid eggs. They did not, however, raise many young as many nests were predated, primarily by Island scrub-jays.
The winter rains are important to dusky orange-crowned warblers as they entice oaks to put forth new leaves. These new leaves provide tender forage for caterpillars which in turn are the primary food source for warblers, especially for nestlings.
In a year with average rainfall the warblers produce an abundance of young. But with climate change models predicting sparser precipation for southern California in the future, the fate of the dusky orange-crowned warbler is precarious.
This article summarizes the information in this scientific paper:
Langin, K. M., Sillett, Terence Scott, Yoon, J., Sofaer, H. R., Morrison, S. A. and Ghalambor, C. K. 2009. Reproductive consequences of an extreme drought for orange-crowned warblers on Santa Catalina and Santa Cruz Islands. In: Garcelon, D. K., Proceedings of the Seventh California Islands Symposium. Institute for Wildlife Studies, pp.293-300.
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