A Chesapeake Barn Owl Population

Abstract

IN conjunction with Osprey (Pandion kaliaetus) studies conducted in Chesapeake Bay, Maryland, from 1963 through 1969 (Reese, 1970), I gathered considerable information on nesting Barn Owls (Tyto alba). Recent nesting failures in some raptorial species, the concentration of the nesting owls in the Chesapeake, and the unusualness and accessibility of their nests prompted this study. Here I present my notes on the owls' nesting success at various stages of their reproductive cycle and compare my findings with those of other Barn Owl studies. This study was made along the shorelines of Talbot and parts of Queen Annes and Dorchester Counties, Maryland (Figure 1). For a description of the territory covered see Reese (1970). In 1963 I found five Barn Owl nests in offshore duckblinds (Figure 2A) in tidewater portions of Talbot County, and for the next 6 years I was able to watch fairly regularly 74 of the 83 nests I located in Talbot and adjoining Queen Annes and Dorchester Counties. The largest number of active nests in one year was 19 in 1967 (Table 1). In 1964 visits were infrequent, but from 1965 on I visited most offshore nests by boat biweekly for 6 months each year, March through August, and made irregular visits during other months. On each visit I recorded the presence of adults and the nest contents. I marked all eggs with a felt-tip pen when first found, banded the fledglings before they left, and managed to catch and band some of the adults. Nests.-All nests included in the study were in offshore duckblinds except one in an old cistern and one in a barrel mounted atop a 20-foot pole. These offshore nesting sites are unusual, though Tomkins (1929) found a Barn Owl nesting in an offshore range light on the lower Savannah River, and Cottam and Nelson (1937) report a similar nesting in a range tower on a marsh plain in South Carolina fully 21/2 miles from the nearest solid land or trees. None of the nests I studied were this far from land, and most of the duckblind sites were less than 200 feet from shore. Most nest sites were active each year of the study. In a few cases where drifting winter ice destroyed their duckblind, the owls nested the next spring in the blind nearest the old nest site. I suspected the same pairs of owls nested at the same sites in consecutive years, but had no marked adults to prove it. Potter and Gillespie (1926), however, caught a banded owl incubating eggs at the same site where it was banded incubating the previous year.