A Significant Summer Encounter

BSBO's Research Director Mark Shieldcastle Writes: On August 8, during the last session of BSBO's Monitoring Avian Productivity and Survivorship (M.A.P.S.) session in the Navarre Marsh (adjacent to where we conduct spring and fall passerine banding studies) we captured a female Myrtle Warbler (the eastern population of Yellow-rumped Warbler). The date was unusual enough, but even more surprising was the fact that the bird had a dried up brood patch and had no presence of molt. 

A "brood patch" is acquired by physiological changes to an incubating bird during the normal nesting behavior. Feathers of the breast and abdomen fall out or are plucked by the bird to permit bare skin to make contact with the eggs or young. Fluid builds up under the skin to increase the ability to transfer heat to the eggs/young. Once the eggs have hatched, there will be a gradual drying of the brood patch as the fluid is reabsorbed. Once the young are fledged the bird will begin its basic molt to the fall plumage. 

The presence of a Myrtle Warbler in this breeding status but without molt is unusual. Generally when this species is encountered in August they are in heavy molt. A capture of this species, which is not recorded to have nested in Ohio, would appear to be a significant capture. These circumstances of brood patch and lack of molt suggest this bird has not traveled very far from its breeding territory before it was captured in our nets.

Breeding condition Myrtle Warbler
captured in BSBO's Navarre Marsh  Breeding
Bird Banding Station on August 8

Checking the Ohio literature finds a report nearest to the Navarre Station was in the Summer 2003 Ohio Cardinal with a female being banded on 2 June at the Darby Unit of Ottawa National Wildlife Refuge which is 7 miles east of Navarre. Farther west of this site, in 1991, The Ohio Cardinal reports a singing male at the Oak Openings Metropark on 11 June. Other sightings during summer include: a single male observed at Lakeshore in late June and above the Quarry at Chapin Forest in June and July, a summering bird in 1996 at Penitentiary Glen (Summer 1997, Ohio Cardinal), summer 1992 a male was encountered at Mohican State Park on 09 June and 12 June with a late migrant on 03 June at Green lawn Cemetery (Summer 1992 Ohio Cardinal), other late spring/early summer records of migrants at Headlands Beach 01 June at Camp Berry and 02 June at Headlands Beach in Summer 2008 (Ohio Cardinal). All of these most likely represent late spring migrants; birds that were waylaid on migration for one of many reasons.

This capture appears to be significant in that it is a documentation of an instance of a possible nesting attempt somewhere near the Navarre Marsh site.  It could have come a short ways from Michigan (but only northern Michigan has known nesting records for the species) or from more northern Ontario. The condition suggests that there was little time between nesting completion and its capture but how close to Ohio we can only contemplate. If only these winged marvels could speak.