Once considered a single species, the Leach’s Storm-Petrel was split into three species in 2016: Leach’s Storm-Petrel, Townsend’s Storm-Petrel, and Ainley’s Storm-Petrel. Although Townsend’s Storm-Petrel can be identified in the field, very little is known about how to identify an Ainley’s Storm-Petrel. They differ from Leach’s Storm-Petrels in only two regards—their vocalizations and the fact that they breed in the winter.
Storm-Petrels spend nearly all of the time on the ocean hundreds of miles offshore, visiting land only a couple months out the year to breed. Therefore, birders are mostly likely to encounter Storm-Petrels on the ocean, where their vocalizations and time of breeding are useless for identification.
Is it possible to identify an Ainley’s Storm-Petrel at sea? The answer may lie in their time of breeding. Birds generally replace their feathers at a time of year opposite to breeding. Because Ainley’s Storm-Petrels breed in the winter, and Leach’s Storm-Petrels breed in the summer, it can be inferred that Ainley’s Storm-Petrel would replace their feathers at opposite times of year, too. This field mark could potentially be useful for identification of Ainley’s Storm-Petrel at sea.
Dessi examined Storm-Petrel specimens to see if he could find any specimens replacing feathers at an atypical time.
Join Dessi as he discusses identification of Ainley’s Storm-Petrel.
Here is a video of the talk: