Introduction
Willow Flycatchers are small flycatchers singing fitz-bew, fizz-bew, and creet! It is difficult to impossible to tell them apart from Alder Flycatchers (Empidonax alnorum) based on appearance alone. The only definite method is to identify them by song. To make it more difficult, in Virginia, these two species share a breeding range in the western half of the state and sometimes overlap in their use of habitat. However, in Virginia, the Willow Flycatcher is more often found in willow thickets with running or standing water nearby (Rottenborn and Brinkley 2007; Lowther 2020; Sedgwick 2020).
Breeding Distribution
Although Willow Flycatchers are found within Mountains and Valleys and Piedmont regions, its likelihood of occurrence is shown only for the Mountains and Valleys (there was inadequate data available for the First Atlas for the Piedmont region, see the Breeding Evidence section for more information on its distribution during the First and Second Atlases in the Piedmont region). In the Mountains and Valleys region, they are most likely to occur in the Shenandoah Valley, Highland County, and the southern Mountains and Valleys region (Figure 1). As this species prefers more shrubby habitats near water, its likelihood of occurring in a block is negatively associated with forest cover.
Within the Mountains and Valleys region, the change in predicted occurrence for the Willow Flycatcher between Atlases declined along the Blue Ridge Mountains and in the southwestern portion of the region (Figures 1 to 3).
Figure 1: Willow Flycatcher breeding distribution based on probability of occurrence (Second Atlas, 2016–2020). This map indicates the probability that this species will occur in an Atlas block (an approximately 10 mi2 [26 km2] survey unit) based on environmental (including habitat) factors and after adjusting for the probability of detection (variation in survey effort among blocks). Blocks in gray are outside the species’ core range and were not modeled.
Figure 2: Willow Flycatcher breeding distribution based on probability of occurrence (First Atlas, 1985–1989). This map indicates the probability that this species will occur in an Atlas block (an approximately 10 mi2 [26 km2] survey unit) based on environmental (including habitat) factors and after adjusting for the probability of detection (variation in survey effort among blocks). Blocks in white were not surveyed during the First Atlas and were not modeled. Blocks in gray are outside the species’ core range and were not modeled.
Figure 3: Willow Flycatcher change in breeding distribution between Atlases (1985–1989 and 2016–2020) based on probability of occurrence. This map indicates the change in the probability that this species will occur in a block (an approximately 10 mi2 [26 km2] survey unit) between Atlas periods. Blocks with no change (tan) may have constant presence or constant absence. Blocks in white were not surveyed during the First Atlas and were not modeled. Blocks in gray are outside the species’ core range and were not modeled.
Breeding Evidence
Willow Flycatchers were confirmed breeders in 30 blocks and 17 counties and found to be probable breeders in an additional 10 counties in the Mountains and Valleys region and the northern part of the Piedmont region (Figure 4). Volunteers observed Willow Flycatchers breeding throughout the Mountains and Valleys and the northern Piedmont region during both Atlas periods (Figures 4 and 5).
The earliest confirmed breeding behavior was recorded in mid-May when nest building and adults carrying nesting material were documented. Breeding was primarily confirmed through observations of adults carrying food (June 2 – July 24), adults feeding young (June 25 – July 30), and recently fledged young (July 12 – August 4) (Figure 6).
For more general information on the breeding habits of this species, please refer to All About Birds.
Figure 4: Willow Flycatcher breeding observations from the Second Atlas (2016–2020). The colored boxes illustrate Atlas blocks (approximately 10 mi2 [26 km2] survey units) where the species was detected. The colors show the highest breeding category recorded in a block. The numbers within the colors in the legend correspond to the number of blocks with that breeding evidence category.
Figure 5: Willow Flycatcher breeding observations from the First Atlas (1985–1989). The colored boxes illustrate Atlas blocks (approximately 10 mi2 [26 km2] survey units) where the species was detected. The colors show the highest breeding category recorded in a block. The numbers within the colors in the legend correspond to the number of blocks with that breeding evidence category.
Figure 6: Willow Flycatcher phenology: confirmed breeding codes. This graph shows a timeline of confirmed breeding behaviors. Tick marks represent individual observations of the behavior.
Population Status
A lack of detections in the point count data prevented the development of an abundance model for the Willow Flycatcher. The North American Breeding Bird Survey (BBS) combines population data for the Willow Flycatcher and Alder Flycatcher to determine their population trends at all scales. However, the BBS data for Virginia do not provide a credible trend at that scale. The population trend estimates for the Appalachian Mountains from 1966–2021 showed a significant increase of 0.53% annually; those for the Piedmont showed a significant 0.98% increase annually (Hostetler et al. 2023; Figure 7). Between the First and Second Atlas, for the Appalachian region, the population trend showed a significant decrease of 1.23% per year, and for the Piedmont region, it showed a nonsignificant decline of 0% per year from 1987–2018 (Hostetler et al. 2023; Figure 7).
Figure 7: Willow Flycatcher/Alder Flycatcher population trend for the Piedmont, Appalachian, and New England/Mid-Atlantic Coast regions as estimated by the North American Breeding Bird Survey. The vertical axis shows species abundance; the horizontal axis shows the year. The solid line indicates the estimated population trend; there is a 97.5% probability that the true population trend falls between the dashed lines. The shaded bars indicate the First and Second Atlas periods.
Conservation
Willow Flycatchers are not considered a species of special concern in the state, and no specific conservation projects are underway.
Interactive Map
The interactive map contains up to six Atlas layers (probability of occurrence for the First and Second Atlases, change in probability of occurrence between Atlases, breeding evidence for the First and Second Atlases, and abundance for the Second Atlas) that can be viewed one at a time. To view an Atlas map layer, mouse over the layer box in the upper left. County lines and physiographic regional boundaries (Mountains and Valleys, Piedmont, and Coastal Plain) can be turned on and off by checking or unchecking the box below the layer box. Within the map window, users can hover on a block to see its value for each layer and pan and zoom to see roads, towns, and other features of interest that are visible beneath a selected layer.
View Interactive Map in Full Screen
References
Rottenborn, S. C., and E. S. Brinkley (Editors) (2007). Virginia’s birdlife: An annotated checklist. 4th edition. Virginia Society of Ornithology.
Sedgwick, J. A. (2020). Willow Flycatcher (Empidonax traillii), version 1.0. In Birds of the World (A. F. Poole and F. B. Gill, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.wilfly.01.
