An evaluation of nest box use by Barn Owls and the initiation of a new box program on coastal marshlands in Virginia

B. D. Watts, The Center for Conservation Biology


In recent years, many North American populations of the Common Barn Owl (Tyto alba) have suffered substantial declines. Explanations for declining trends vary regionally but include secondary succession on cleared lands, intensification of agricultural practices, biocides, and urban development. In Virginia, the Barn Owl is considered an uncommon to rare resident species. Population strongholds continue to be the Shenandoah Valley, the northern Piedmont, and the open marshlands of the Coastal Plain. From 1976 to 1985 there were 111 documented nest sites for Barn Owls in Virginia but only 43 of these sites supported active breeding pairs in 1986. During that year, the Virginia Department of Game and Inland Fisheries (VDGIF) initiated a nest box program in an attempt to reverse recent population trends. The objectives of this project were to 1) resurvey VDGIF nest structures to evaluate condition and use, and 2) to expand the nest box program in Virginia by establishing a new network of boxes within extensive open marsh habitats of the Coastal Plain. During the breeding season of 1997, 71 boxes and trays were examined throughout Virginia including 30 in the ridge and valley region, 21 in the piedmont, and 20 in the coastal plain. Twenty-one of 71 (29.6%) VDGIF boxes were found to be active during the 1997 breeding season. An additional 25 boxes appear to be available for use but were not used during the 1997 breeding season. Fifteen boxes erected between 1986 and 1990 had been destroyed. Five boxes were judged to be currently unusable by nesting Barn Owls. Overall, the rate of occupation by breeding Barn Owls was very similar to that reported in 1989 and 1990, the last two years that nest boxes were monitored. More than 45% of boxes that were judged to be available for use supported active pairs. This evaluation demonstrates that the aggressive use of nesting substrates within appropriate locations could have a significant impact on Virginia’s population and highlights the need for a broad-based management plan that outlines the remaining strongholds for this species and identifies specific locations where management actions would have the greatest probability of success. Extensive short-grass marshes are the most natural and stable foraging habitats available to Barn Owls in Virginia. Providing nesting substrate within these foraging habitats is a logical progression in the management of this species. A total of 60 nest boxes that were specifically designed for use in coastal marshes were constructed. A network of 44 boxes were established within extensive open marshes. The remaining 16 boxes have been, or will be, installed within inland sites with appropriate grassland habitats. The initial 24 nest boxes that were deployed in 1997 were monitored for 2 years after establishment. This effort did not identify any indication of use during this time period. A follow-up survey of all box sites is needed to adequately evaluate the success of this effort. Such a survey could evaluate both the longevity and condition of the marsh boxes and give an indication of their use.