Difficult Decisions: Identifying Female Warbler Species

Which are the most difficult wood-warbler female species to identify from one another?

All rise and bow to the Lord of Warbler Identification, as how doth one begin to compile such a lengthy list?

It includes such opponents as Wilson’s vs. Hooded; Yellow-Rumped vs. Cape May; Common Yellowthroat vs. Wilson’s; Wilson’s vs. Yellow; Bay-Breasted vs. Blackpoll (in late summer/autumn) – and I’ve just begun to scratch the surface of this identification game conundrum.

An interesting treatise on this topic appears at the following web site address:

http://www.tucsonaudubon.org/birding/duos25.htm

Here, the author (Larry Liese) explores how to distinguish female Yellow, Wilson’s, and Common-Yellowthroat from each other.

(The illustrator of the above graphic is George C. West.)

Which wood-warbler populations have fallen precipitously in recent years?

If your answer included "Cerulean Warbler," then you're correct.

Based on information at Cornell of Ornithology's web site (http://www.birds.cornell.edu/cewap/index.html), this Neotropical migratory bird species continues to experience population declines in parts of its range. However, given the Ceruleans low population density and patchy distributions, accurate population trends are difficult to estimate. One ongoing, annual monitoring program -- the Breeding Bird Survey, coordinated by the US Geological Survey -- has compiled data that suggest a 3.8 percent annual decline in populations of Ceruleans since 1966. To adequately protect this species more information is needed about its habitat requirements, breeding biology, and population status, the Cornell web site suggests.

To determine the number of breeding pairs and productivity, describe nesting habitat, and identify potential threats to the population and its habitat, the Cerulean Warbler Atlas Project (CEWAP) employed enthusiastic birders and biologists to survey known and potential Cerulean Warbler breeding sites from 1997 to 2000.

Results from CEWAP will be used to produce management guidelines for Cerulean Warblers. As of December 2000 you can download the final report, "An Atlas of Cerulean Warbler Populations," by conducting a Google search with the aforementioned title in quote marks.

Lucky 19: Kirtland's Warbler Update in Wisconsin

(Above, a fledgiing Kirtland's Warbler in Adams County, Wisconsin. Copyright Joel Trick, Wisconsin DNR.)

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According to a Wisconsin DNR news release from July 6, 2009, 19 Kirtland's Warbler young have hatched in the state this breeding season.

(As background information for the uninitiated, historically and through 2006, Michigan was considered the endemic breeding range of this species. Only periodic, non-annual sightings were reported in Ontario (including one nesting record in 1945) and Wisconsin, with no documented nests ever found in Wisconsin. This scenario changed in 2007 when Kirtland's was confirmed as a nester for the first time in Wisconsin.)


Here's more information about the ongoing monitoring in 2009 of Kirtland's Warbler within two Wisconsin counties:

Adams County

Wisconsin Kirtland’s warblers have had an extremely successful nesting season in 2009, and have already surpassed the reproductive output of last year. As of today, at least five Adams County nests have fledged young, including two nests that each produced four young over the weekend. So far a biologist has determined that the nests that have fledged contained a total of 19 young when checked just prior to the young leaving the nest. Another nest that is currently being incubated is expected to hatch within the next week or so. This nest is the renesting effort of a pair that had previously been parasitized by cowbirds. One nest that was expected to fledge soon was empty today, and the behavior of the adults suggests it may have been lost to predation. The biologist has currently been unable to find the nest of one additional pair at the site, but he will continue to search in the days ahead.

Marinette County

Male Kirtland’s warblers are known to be present at two separate sites in Marinette County, and each has previously been observed with a female. On Thursday, a DNR volunteer monitor found a nest containing three eggs at one of these sites. Finding eggs at this late date suggests that this may be a renest after an early failure. If successful, this would be an important nesting record for Marinette County. We will continue to monitor this nest to determine its outcome.

Which wood-warblers are known to feed on fruits and nectar?

Many of North America’s wood-warblers consume fruit and nectar, especially during the non-breeding season.

Three of the most notorious species are Dendroica congeners Yellow-Rumped, Black-Throated Blue, and Cape May Warbler. (Some Vermivora genus members, too, are known for eating fruits/nectar, given they probe well with longer, thinner bills than Dendroica genus members’ that have bills primarily adapted for insect eating.)

Yellow-Rumped populations during the non-breeding season often remain in far northern latitudes in comparison to other wood-warbler species that are obligatory migrators forced to vacate areas where they breed. Yellow-Rumped is often able to remain in northern climes throughout the winter (e.g., Wisconsin and New England during some, but NOT all, non-breeding seasons) because, depending on its location, may subsist on foods such as poison ivy berries, wax myrtle berries, and/or privet berries – fruits, in fact, from which the majority of other songbirds are unable to derive much energy.

Black-Throated Blue, likewise, are documented to
eat small berries and fruits. They also feed at flowers, possibly for nectar or insects. During the non-breeding season in the Dominican Republic, this species feeds frequently on honeydew-like excretions from scale insects.

As for Cape May, non-breeders are often easily observed and are known to feed on nectar, among other things, taken up by means of a semi-tubular tongue. They also eat insects and fruit from Cecropia trees, grapes and grape juice, and tree sap. In some cases, this species has caused damage to commercial vineyards in Indiana, Pennsylvania, and W. Virginia by puncturing grapes, thereby damaging all grapes not bagged.

As a personal observation note, I remember several autumns in Wisconsin and Maryland when I watched transient Black-Throated Blue feeding on various berries. Staking out the same patch of shrubs each autumn invariably resulted in the presence of watching the berries disappear over a few days – while I enjoyed seeing female, male, and hatch year individuals of this species up close.