Evidence for Northern Waterthrushes Breeding in Southeast Wyoming

The Northern Waterthrush ($eiurus noveboracensis) is an uncommon but regular visitor to Wyoming during migration and has been documented across much of the state (Dorn and Dorn 1999, Luce et al. 1999).It is suspected to breed at least occasionally in Teton County in northwestern Wyoming (Dorn and Dorn 1999, Luce et al. 1999).In southeastern Wyoming, 20 miles west of the city of Laramie along the Little Laramie River, 11 individuals were captured during three seasons of bird banding for a MAPS (Monitoring Avian Productivity and Survivorship) study.During the summers of 2000, 2001, and 2002 six individuals were recaptured within the same year and three were recaptured in more than one year.Four males and three females were in breeding condition.For three months in 2002 at least two waterthrushes established territories along a small portion of the river, as evidenced by singing males observed each day of MAPS operation.If territories were established during the 2000 and 2001 seasons they remained undetected.The Northern Waterthrush is known to breed from Virginia north through the northeastern United States, west across much of Canada and Alaska, and south through the Rocky Mountains of Idaho and western Montana (Eaton 1995, American Ornithologists' Union 1998).Disjunct populations are known from northern North Dakota, southern Manitoba, and Saskatchewan.These outposts lie relatively close to the species' core range farther north, but another oufiying population, in southcentral Oregon, is approximately 400 miles from the main breeding range in the northern Rocky Mountains (Eaton 1995).Northern Waterthrush breeding has been recenfiy documented twice along the Michigan River in north-central Colorado and is suspected more widely in the area (Kingew 1998).These observations were approximately 45 miles south of capture locations along the Little Laramie River in Wyoming and 350 miles southeast of the known southern limit of distribution in the Rocky Mountains (Figure 1).Although Wyoming was not mentioned specifically by the AOU (1998) or Eaton (1995), the Northern Waterthrush is a rare summer resident in the northwestern part of the state and an uncommon migrant throughout (Dorn and Dorn 1999, Luce et al. 1999).Most Wyoming observations have been presumed to represent migrants, a presumption that may need to be reconsidered in light of recent evidence of breeding in the southeast.During three seasons of MAPS banding, I captured five males, two females, one juvenile, and three individuals of unknown sex and age between 3 June and 6 August (Table 1).Each year's banding schedule consisted of a total of seven days each separated by at least one week.Sex was determined by the presence of a cloacal protuberance or brood patch, age by plumage or molt.Three individuals were captured over two consecutive seasons, and six were captured twice during a single season.It was unclear if the juvenile was fledged locally or captured during migration, but the same individual was recaptured the following year.Although external sexual characters can persist after breeding, the presence of these characters in combination with consistent recaptures, the capture of a juvenile, and the detection of at least two territories along 700 m of the stream are strong evidence for local breeding.This finding raises two related questions.First, were Northern Waterthrushes

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