As mentioned earlier, Yellow-rumped Warblers were previously divided into two species, Audubon's Warbler in the west, and the Myrtle Warbler in the east. Their phylogenetic differences are thought to have evolved during the Wisconsin glacier which divided eastern and western populations.
The divergent populations probably came into contact again about 7500 years ago and now interbreed where their ranges meet, in the passes of the Canadian Rockies. Because of their interbreeding in this area, the hybrid zone extends 150 km in either direction and will probably continue to grow as time passes. It has been calculated that it will take more than 6 million years for these taxa to completely fuse (Barrowclough 1980; Gill 1995; Zink and McKitrick 1995).
Perception Channels: visual ; tactile ; acoustic ; chemical
The Yellow-rumped Warbler is abundant throughout its range and is probably the most abundant of all warbler species. The Breeding Bird Survey and the Christmas Bird Count in the last 25 years have shown that populations of the Yellow-rumped Warbler are rising at around 2% (or less) per year (Stokes and Stokes 1996).
US Migratory Bird Act: protected
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
IUCN Red List of Threatened Species: least concern
No known negative impacts on humans.
As an insect eater, the Yellow-rumped Warbler may benefit humans by eating potentially harmful (or painful) insects.
The Yellow-Rumped Warbler feeds mainly on insects in the summer and on berries and fruit in the winter. Yellow-rumped Warblers are capable of assimilating 80% of wax-coated berries such as bayberries. They have developed unique gastrointestinal traits to allow them to subsist on this unusual food source.
The Yellow-Rumped Warbler comes to bird feeders for fruit and suet (Gill 1995; Stokes and Stokes 1996; Granlund 1999).
The Yellow-rumped Warbler has a large breeding range. During the spring and summer in the western side of its range, it can be found as far north as central Alaska and as far south as Central America. Its breeding range stretches across Canada, but in the eastern United states, the Yellow-Rumped Warbler is only seen as far south as the Great Lakes states.
The winter range extends from the southern states to the West Indies and Central America. The Yellow-rumped Warbler is a facultative migrant (it moves with food availability and weather) and so has a drastically changing winter range depending on yearly conditions (Stokes and Stokes 1996; Granlund 1999).
Biogeographic Regions: nearctic (Native ); neotropical (Native )
A highly adaptable bird, the Yellow-rumped Warbler can be found in a variety of habitats including coniferous forest, mixed woodlands, deciduous forest, pine plantation, bogs, forest edges, and openings. In the winter it is often found in brushy thickets of bayberry and wax myrtle (Stokes and Stokes 1996; Granlund 1999).
Terrestrial Biomes: taiga ; forest
Average lifespan
Status: captivity: 6.9 years.
Birds of either sex in all plumages have a yellow rump and a yellow patch on their side just in front of each wing. During the breeding season, male and female also have a yellow crown patch and white tail patches. There are two subspecies (previously considered separate species), the north and eastern Myrtle Warbler and the western Audubon's Warbler. The breeding male Myrtle Warbler has white eyebrows, a white throat, and white sides of neck while the Audubon's Warbler has no eyebrows and a yellow throat. Females and non-breeding males show the same basic pattern but are duller in color than their breeding counterparts (Stokes and Stokes 1996; Dunn 1999; Georgia Wildlife Website 2000).
Other Physical Features: endothermic ; bilateral symmetry
Average mass: 11.5 g.
Average basal metabolic rate: 0.1895 W.
The Yellow-rumped Warbler breeds in monogamous pairs. A neat cup made of twigs, bark strips, rootlets, and lined with grasses, hair, and feathers serves as a nest for the Yellow-rumped Warbler. The nest is placed on a horizontal branch near the trunk of a conifer tree 5 to 50 feet in height (the average height of the nest is 20 feet). The outside diameter of the nest is 7.6 to 8.9 cm.
Four to five cream eggs with brown spots are laid, and incubation lasts 12 to 13 days. The chicks are altricial and fledge 12-14 days after hatching. Two broods may be raised in a season (Stokes and Stokes 1996; Granlund 1999; Georgia Wildlife Website 2000).
Key Reproductive Features: iteroparous ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; oviparous
Average time to hatching: 12 days.
Average eggs per season: 4.
