Category: Non-Game Management and Conservation
Published: August 19, 2010
Author(s): David H. Johnson, Donald C. Gillis, Michael A. Gregg, James L. Rebholz, Jeffrey L. Lincer, and James R. Belthoff
Western Burrowing Owl (Athene cunicularia hypugea) populations have been declining across nearly all portions of their North American range (Klute et al. 2003). Range contraction and fragmentation is a significant concern for this owl. Artificial Burrow Systems (ABS) have been in use since the 1970â€™s, and this management tool has been thoughtfully studied and refined since its inception. In this Users Guide, we provide a synthesis of material relevant to the use of ABS for Burrowing Owls, insights into the placement of ABS, design specifications and installation techniques, and fundamental anti-predator strategies.
ABS should not be designed to simply maintain the species (with the exception of the Imperial Valley of California, the species is not maintaining itself now over most of its range), but rather should meaningfully contribute to slowing the rate of population decline, and directly help in the recovery and conservation of the species. Additionally, burrow systems need to be simple in design, very low-cost, easy to install and maintain, durable, and very efficient. We recognize that this is a lot to ask of artificial burrows. Further, the fundamental underlying issue here is the loss of habitat as well as the persecution and loss of the mammal species (e.g., badger, prairie dog, ground squirrels) which have historically provided the burrows that the owls use. Thus, while ABS are genuinely helpful, they address only part of the real conservation issue occurring in our open grassland, sagebrush and arid-land communities. The use of artificial nest structures is not new to wildlife conservation nor to owls, specifically, as a number of cavity-nesting forest owl species are supported largely by wooden nest boxes in Finland (Saurola 2009). This does not mean that boxes are preferred as a management method over natural sites (they are not), but given other ecosystem management systems, the only operational choice is the use of nest boxes as a conservation safety net for the owls.
In this document we first examine the dimensions of burrows made by the main fossorial mammal species, i.e., American Badger (Taxidea taxus), Black-tailed Prairie Dog (Cynomys ludovicianus), and various species of large ground squirrels (Spermophilus spp.), that provide the burrows used by burrowing owls. We then offer a review of other ABS designs, and follow that with details on an ABS design that reflects the combination of features from other ABS systems, and integrate elements that we have found successful in our work.
We suggest two artificial burrow system (ABS designs): one design employs the use of half of a 208 l (55-gallon) barrel for the nest chamber (i.e., 50 cm, 20 in., in diameter, 1960 cm2 interior floor space) and two stacked 9.5 l (2.5 gal.) buckets on top for access. The main tunnel is a 2.4 m (10-ft) section of 15 cm (6 in.) diameter corrugated flex drain pipe with a 7.5 cm (3 in.) slot cut out of the bottom to provide a dirt walkway for the owls), and an anti-predator patio. The occupancy rate of this design through the 2010 nesting season (with 59 units in place) on a northeastern Oregon study site has been 86%. Our second design is this same basic concept, except that we use a 10 cm (4-in.) diameter flex pipe main tunnel without a walkway slot, rather than the 15 cm diameter version. As owls have shown a clear preference with sites that have many burrows, a minimum of two (or three) burrow units should be placed at a given site (about 5-10 m apart). We also make recommendations as to selection criteria for placement of the ABS system, and specifics on short perches (i.e., <60 cm, 24 in.) and related anti-predator aspects.