Ceruleans have a fascinating migration, crossing the Gulf in spring making landfall mostly in the eastern Gulf in mid-April. Most seem not to make landfall on the coast at all, and the above animation shows that they just “magically” appear on the breeding grounds. Increasingly it is thought that warblers like Cerulean may do more of their migration in non-stop hops, jumping directly from Central America to breeding grounds in the Appalachians. For birders on the Gulf Coast, spotting a Cerulean is a real treat, and that fact along with the animation above give some support to the theory of a longer non-stop flight. Watch the fall migration in this species–they just fade away. Ceruleans are early migrants, rarely seen in September, and are among the toughest fall migrants to detect. It may be that their departure is in another non-stop flight and with the birds being silent on southward passage, the STEM map doesn’t even show the extremely low probability of finding one in fall migration.
This is not one of the very best animations and anyone familiar with the distribution of the species will spot some problems. The summer distribution shows lows of “bleed” on Coastal Plain areas where they don’t occur. They essentially never occur in northern Maine. As is usually the case with STEM results that are of lower quality, the species has a very low predicted occurrence rate of 0.002 to 0.006. An ongoing research topic will be to learn how to improve these models for rarer species. Will increased data volume solve the issue for us? Must we have more eBird surveys in northern Maine to “prove” to the models that Ceruleans do not occur there? As future iterations of these maps become available, we hope to answer those issues and provide even more accurate maps.