Winter Composition of Nelson’s Sparrow (ammodramus Nelsoni) and Saltmarsh Sparrow (ammodramus Caudacutus) Mixed Flocks in Coastal Virginia

—We captured 1,055 Nelson’s (Ammodramus nelsoni) and Saltmarsh (Ammodramus caudacutus) sparrows during the winter season (2006–2014) within the outer Coastal Plain of Virginia to determine the composition of subspecies. Birds were captured using mist nets in 24 tidal salt marshes and identified to subspecies using a plumage-based, syntopic key. Contrary to previous assessments, both species of sharp-tailed sparrows were common. All five subspecies were present and appeared to form mixed flocks within patches. The north-Atlantic Saltmarsh Sparrow (A. c. caudacutus) was the most common form, accounting for 45% of all birds identified to subspecies. The three Nelson’s Sparrow forms including the “Acadian” Nelson’s Sparrow (A. n. subvirgatus), “James Bay” Nelson’s Sparrow (A. n. alter) and the “Nelson’s” Sparrow (A. n. nelsoni) were equally common and collectively accounted for 47% of the subspecies identified. The highly restricted, mid-Atlantic Saltmarsh Sparrow (A. c. diversus) was the least common, accounting for only 8% of individuals. Subspecific composition did not vary with geography in the region. Age ratios for both Nelson’s and Saltmarsh sparrows were significantly skewed to hatching-year (HY) rather than after-hatching-year (AHY) birds. However, age ratios varied dramatically across years for both species. The annual portion of birds accounted for by the HY class ranged from 31.3 to 77.5% and 36.7 to 70.3% for Nelson’s and Saltmarsh sparrows, respectively. Information from Virginia represents a significant extension of current perceptions about the winter distribution of these forms. Received 19 September 2014. Accepted 15 February 2015.