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A Kirtland's warbler nestling in Wisconsin is measured.  Photo courtesy of Joel Trick

A Kirtland's warbler nestling in Wisconsin is measured. Photo courtesy of Joel Trick.

Kirtland's Warblers in Wisconsin: 2014 Nesting Season

Kirtland's warblers are recent colonizers to Wisconsin. The first confirmed nesting in Wisconsin was in Adams County just eight years ago. The number of males recorded in Adams County since that first discovery has ranged from 7 to 16. The core Kirtland's breeding population, which was discovered over 100 years ago, is located in central Michigan and consists of approximately 2,000 singing males. The Michigan population has been on an upward trajectory since the 1990s and is surveyed annually.

In Wisconsin, we have been keeping close tabs on the Kirtland's warbler nesting population in Adams County, as well as in northern counties where a few single males have been observed.

The 2014 Kirtland's season started the second week in May when a male, singing atop a red pine, was identified by its color-bands at the Adams County site. A female arrived at the site only a week later. More males and females arrived at the site in May, and for us, the monitoring field season was in full gear. Males established territories and paired with females, males defended territories, females constructed nests, eggs were laid and incubated, and within a few months' time nestlings hatched and fledged.

So, what exactly happened during the 2014 season?

Eleven males and seven females were confirmed at the Adams County site, with 64 percent of the males and 29 percent of the females banded in previous nesting seasons. Seven males paired with seven females. Eight nesting attempts were made by seven pairs, with one pair renesting. Three nests successfully fledged a combined total of eight to10 young. Three nests failed and were most likely predated, and two nests were parasitized, fledging cowbird chicks.

In comparing the 2014 nesting season to past nesting seasons, 2014 had a lower number of pairs and nests compared with previous years, except for 2008 which had five pairs and five nests. This year had a slightly lower number of successful nests compared to most previous years, but the greatest percentage of successful nests (38 percent) since 2009. Estimated fledgling success was low compared to the estimated success in 2009-2011 and 2013, yet comparable to 2008 and 2012.

The banding crew captured six and banded five adult males during the 2014 season; one male was a recapture and previously banded at the site in 2013. Four adult males were color-banded in Adams County and one was color-banded in Bayfield County. Three adult females were captured and two were banded in Adams County (one was a recapture, previously banded at the site in 2013).

Our new initiative to color-band nestlings was a success, and six nestlings from two nests were banded. All six nestlings were observed to have fledged the nests successfully. We will continue to band nestlings next season and are eager to observe if the nestlings banded this year return to Wisconsin.

Cowbird traps were again used in a continuation of a management program dating to 2008. Four traps were placed at the Adams County breeding site and 110 cowbirds were captured -- 100 males and 10 females. The number was lower than in past years. We will continue to use traps next season.

Statewide, the annual Kirtland's warbler census, which occurred June 6-20, yielded 13 singing males. This year, 41 sites in six counties were surveyed by 11 volunteers. Most of the males were detected at the Adams County site, while two were detected in the northern Wisconsin counties of Bayfield and Marinette.

Another new initiative this year was the use of playbacks at four sites. The hypothesis being tested is that the use of Kirtland's song may attract them to viable nesting areas. Playbacks were established in Bayfield County Forest, Chequamegon-Nicolet National Forest, Vilas County Forest and Marinette County Forest. One male Kirtland's was observed at the playback site in Bayfield. No Kirtland's were detected at the other three sites. We will continue this experiment in 2015.

The Wisconsin Kirtland's Warbler Project is a close partnership among the Wisconsin Department of Natural Resources, U.S. Fish and Wildlife Service, U.S. Department of Agriculture APHIS-Wildlife Services, Plum Creek Timber Co. and Timberland Investment Resources, the Natural Resources Foundation of Wisconsin and many dedicated volunteers.

By Sarah Warner
Green Bay, Wisconsin Ecological Services Field Office (Madison)

This article was written for The Badger Birder, monthly newsletter of the Wisconsin Society for Ornithology.

Last updated: January 7, 2015