Griffon Vultures &Lpar;<I>Gyps Fulvus</I>&Rpar; Ingesting Bones At
SEPTEMBER1997 LETTERS 287 AravaipaCreek, Arizona. Almost immediatelyat leastsix Elf Owls beganvocalizing from dispersedlocations around our campsiteand at leastfour of them began making low passesat the Great Horned Owl. Before we could relocate the horned owl to a protectedenclosure, it wasstruck once in the head by an Elf Owl. Some nocturnal behaviorsmay not be well known or understood,not becausethey are rare, but becausethey are difficult to observe.This may changewith the increasedavailability of night vision equipment (P. Henson and J A Cooper 1994, Auk 111:1013-1018). Currently, observationsof nocturnal behaviorsare likely to be sporadicand anecdotal,and therefore unreported. Such information, however,may help in understandinga speciesbiology. For example, other researchershave observedgroup mobbing by Elf Owls (F.R. Gehlbach,pers. comm.; B.A. Millsap, pers. comm.), but there are no publishedreports of the behavior.Our observations,and thoseof other researchers, suggestthat Elf Owlswill join together in mobbing and that they can be physicallyaggressive when defending their nestsagainst predators. We thank A. Duerr, T.S. Estabrookand R.L. Spauldingfor assistingwith the observations.We alsothank T. Brush, ER. Gehlbach, R. Glinski, P. Hardy, B.A. Millsap, G. Proudfoot and H.A. Snyder for sharing their observational information concerning mobbing by small owls.This manuscriptbenefitted from the constructivereviews of ER. Gehlbach,C. Marti, B.A. Millsapand an anonymousreviewer.--Clint W. Boal, Brent D. Biblesand R. William Mannan, Schoolof RenewableNatural Resources,University of Arizona, Tucson,AZ 85721 U.S•. j. RaptorRes. 31 (3):287-288 ¸ 1997 The Raptor ResearchFoundation, Inc. GRIFFONVULTURES (GYPS FULVUS) INGESTING BONES AT THE OSSUARIESOF BEARDEDVULTURES ( GYPAETUSBAR•ATUS) Some African vulturesovercome the calcium deficiencyin their diets by ingestingbone fragments,and are depen- dent on the presenceof largepredators to supplythem (Mundy and Ledger 1976, S.
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