SELECTIVE USE OF NEST LINING MATERIALS BY BURROWING OWLS

1. DISCUSSION • Negative relationships between the distance to the nearest source of manure and both the weight and proportion of manure, suggests that owls use manure in proportion to it’s convenience and availability in the landscape. • The frequent use of grass to line nest burrows, and the selective use of grass divots during our selection experiments, suggests that the use of grass to line nest burrows also serves some adaptive function. • Hypotheses to explain the adaptive function for use of manure to line nest burrows should also explain the preferential use of grass. • We are currently testing 3 adaptive hypotheses to explain nest-lining behavior: olfactory camouflage, prey attraction, and burrow ownership. SELECTIVE USE OF NEST LINING MATERIALS BY BURROWING OWLS Matthew Denman Smith and Courtney J. Conway Arizona Cooperative Fish and Wildlife Research Unit, The University of Arizona, Tucson, AZ • DO BURROWING OWLS SELECTIVELY CHOOSE MANURE TO LINE THEIR NEST BURROWS? • INTRODUCTION • Burrowing owls, Athene cunicularia, often collect and line the entrance and tunnel leading down to their nest chamber with dried mammal manure (Bendire 1892), shredded carpet, paper, plastic, cotton, golf course divots, tin foil, and / or other mateials (Thomsen 1971, pers. observ.). • The adaptive function of foreign objects brought to the nest is not well known in burrowing owls. • Despite the presence of other materials, hypotheses to explain the nest-lining behavior have exclusively focused on the use of manure. • Possible hypotheses to explain the function of nest-lining behavior include: olfactory camouflage from predators (Martin 1971, Green and Anthony 1989), insulation (Martin 1971), absorption of water for flood protection (Greibel 2000), and reduction of carbon dioxide levels (Brady and Beltoff, pers. comm.). An alternative hypothesis that has not previously been tested is the attraction of insect prey. • Some hypotheses predict that owls should preferentially choose manure to line their nest burrow, whereas other hypotheses adequately explain the use of materials other than manure. Hence, understanding the degree to which owls actively choose manure over other possible nest-lining materials may help discriminate among possible adaptive explanations of this odd behavior. • The urban, industrial, agricultural and ranching communities of south-central WA provide a unique opportunity to study the selection of nest-lining materials, because manure is readily available in some areas where burrowing owls nest, but not in others. RESULTS Figs 4&5. Owls preferred manure and grass divots and avoided carpet and tin foil as nest-lining material in our supply-station selection trials. We detected no difference between the amount of manure and grass divots selected. • METHODS • Supply Stations • At each of 12 randomly-selected nest burrows we supplied 2 liters of 4 types of materials often found at burrowing owl nests: carpet pieces (260 g), grass divots from golf courses (330 g), dried manure (510 g), and tin foil (70 g).   • We placed the materials at a random azimuth, 10 meters away from each nest burrow.    • Material Collection • At 21 randomly-chosen nest burrows we collected, dried, and weighed all foreign material found on the burrow mound and within the first meter of the nest tunnel. • We measured the distance to the nearest source of manure at each of the 21 nest burrows. Manure Proportion Manure Weight ACKNOWLEDGEMENTS Thanks to our field workers: C. Forristal, D. Hearne, M. Hearne, T. McLaughlin, S. Millus, P. Ramey, C. Sanders, and A. Sanfacon. Special thanks to Sandpiper Technologies and the American Museum of Natural History’s Frank Chapman Memorial Research Fund. REFERENCES Bendire, C.E. 1892, in: Bent A.C. 1938. Life Histories of North American Birds. U.S. Nat. Mus. Spec. Bull.1. Green, G.A. and R.G. Anthony. 1989. Nesting success and habitat relationships of burrowing owls in the Columbia basin, Oregon. Condor, 91:347-354. Griebel, R.L. 2000. Ecological and physiological factors affecting nesting success of burrowing owls in Buffalo Gap National Grassland. Master’s Thesis. University of Nebraska. Marshall, A.J. 1954. Bower-Birds: Their Displays and Breeding Cycles. Oxford: Clarendon Press. Martin, D.J. 1973. Selected aspects of burrowing owl ecology and behavior. Condor, 75:446-456. Thomsen, L. 1971. Behavior and ecology of burrowing owls on the Oakland municipal airport. Condor, 73:177-192. Vellenga, R. 1970. Behaviour of the male satin bowerbird at the bower. Austral. Bird Bander, 1:3-11. Yosef, R. 1999. Function of stone carpets at the nest entrance of blackstarts Cercomela melanura. Vogelwelt, 120(3): 155-161. Figs 1&2. Proportion of manure in nest-lining material decreases as the distance from a source of manure increases. Fig 3. Grass and manure are the most common nest- lining materials used.