Occurrence Maps

Dusky Flycatcher

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Dusky Flycatcher is a breeding bird of western mountain forests and brushy mountain sides. It migrates mostly west of the Rocky Mountains to winter in western Mexico, heading north in April and May, and south from August-October.

Like Willow Flycatcher, Dusky Flycatcher is an Empidonax flycatcher, a genus that is renowned for containing some of the toughest identification challenges in North America. Given how hard they are to identify, we are very pleased that this model built on eBird data shows so accurately the breeding range and the spring migration pattern that we have come to understand over recent decades. The summer maps show the species restricted to mountains, such as the Sierra Nevada and San Berndardino ranges in California. In spring migration, they are spread out a bit more, as they pass through lowland deserts on their way north. In this respect, the migration map is similar to the one for Western Tanager.

However, like Kentucky Warbler and Wood Thrush, Empidonax flycatchers can be secretive during migration, and like those species, the transition from summer to fall simply shows the species fading out. Not only are Empidonax secretive in fall, but they are also harder to identify, since they do not sing their diagnostic songs, and at best give you a few ‘whit’ notes with which to identify them. It may very will be that the challenge of identifying Dusky Flycatchers in fall exacerbates the detectability problem and causes these maps to mostly “miss” the southward passage. (As always though, an adjustment to the scale may bring the southward movement to the fore a bit better). In this respect, the Western Tanager map is quite different, since the southward passage of that conspicuous fall migrant shows up quite well. This map highlights the need to account for seasonal changes in detectability in order to understand bird abundance, instead of simply occurrence (which is really predicting the likelihood of a birder finding the species at these seasons). This is one of our many research directions in relation to these models.