Great Horned Owl (Bubo virginianus) Thomas Carpenter
Lake Erie Metropark, Wayne Co., MI 2/22/2009 © Joan Tisdale (Click to view a comparison of Atlas I to II)
It’s a cold winter night just before dawn. Off in were in the southern LP. Although this trend may be somewhat accurate ─ the more the distance a series of low hoots resonate extensively forested northern LP and UP through the still air. This scenario plays out probably contain less favorable habitat ─ Great across the state, as Michigan’s notorious ‘hoot’ Horned Owls were undoubtedly easier to detect owls proclaim their breeding territories. A in the small, scattered woodlots that characterize permanent resident from southern South the southern LP. Coverage was also more America to the tree line of the arctic, the Great extensive in the southern LP. Thus, both atlases Horned Owl breeds throughout Michigan probably underestimated the species distribution (Houston et al. 1998). in the UP and northern LP.
Distribution Overall, there were more reports of Great The continuous forest that characterized the Horned Owls in MBBA I than MBBA II. state prior to European settlement afforded poor Statewide, MBBA I detected Great Horned habitat for Great Horned Owls, which were Owls in 34.7% of townships versus 18.3% probably restricted to the forest edge and during MBBA II. The difference is largely due occasional clearings. The clearing of the forest to fewer reports in the LP during MBBA II. For created more favorable habitat, but the owls the southern and northern LP, MBBA I reported were persecuted throughout the early part of the the species in 55.6% and 32.0% of townships, 20th century due to their proclivity to respectively; the percentages fell to 28.9% and occasionally kill poultry and small game. As 10.9% for MBBA II. UP reports are consistent agriculture became more specialized, fewer for both atlases at 13.4% and 13.3% of farms raised poultry, and those that did kept townships, respectively. Most likely, there was birds indoors where they were less available to less effort to locate Great Horned Owls during predators. This change, coupled with the MBBA II rather than an actual decline in passage of protective legislation, allowed Great abundance since MBBA I. Horned Owls to proliferate starting in the 1940s
(Peterjohn and Rice 1991). Great Horned Owls do not construct nests; they
rely on nests of other raptors, tree cavities and Both MBBA I and MBBA II recorded the the tops of broken trees to breed. Thus, wooded species throughout the state. During both areas with suitable nesting structures and open atlases, most probable and confirmed records
© 2011 Kalamazoo Nature Center Great Horned Owl (Bubo virginianus) Thomas Carpenter areas for hunting seem to be the primary habitat first appeared in Michigan, the West Nile virus requirements. There may be a preference for was thought to be particularly detrimental to hardwood and mixed forests (Petersen 2006), Great Horned Owls (Gancz et al. 2004) but but research on the habitat utilized in areas with research in Wisconsin suggests that it has had coniferous forest is needed for confirmation. no detectible effect on breeding populations The species also occurs in suburban woodlots (Stout et al. 2005). and urban parks. Conservation Needs Breeding Biology No specific management is needed for Great Breeding populations appear to be limited by Horned Owls; Michigan populations appear to the ability to successfully establish territories be stable. Erection of artificial nests may entice (Rohner and Krebs 1998), and non-breeding, birds to nest in less mature woodlots that lack non-territorial floaters can form a substantial naturally occurring nest sites, and could portion of some populations (Rohner 1997). facilitate research and educational opportunities. Not all territorial pairs breed every year; 10- As top predators, Great Horned Owls 38% of pairs failed to breed in southern accumulate contaminants from their prey and Wisconsin and southern Ohio, respectively are therefore susceptible to secondary poisoning (Petersen 1979, Holt 1996). During the lowest (Sheffield 1997, Houston et al. 1998). point of the snowshoe hare cycle in the boreal Rodenticides (Stone et al 1999), forest of Canada, no pairs of Great Horned Owls organochlorines (Blus 1996) and lead shot attempted to breed (Rohner and Krebs 1998). (Clark and Scheuhammer 2003) have caused Once they establish a territory, birds are thought mortality. Great Horned Owls that inhabit areas to occupy it for life (Houston et al. 1998). near human dwellings may be particularly susceptible to rodenticides given their Abundance and Population Trends propensity to feed on rats. Great Horned Owls are not readily censused by the breeding bird survey, which shows a nonsignificant decline for Michigan for the years 1966-2007 (Sauer et al. 2008). The Christmas Bird Count could potentially provide information on population trends, but changes in its methodology are required in order to accurately quantify owls. The upcoming Michigan Bird Conservation Initiative (MiBCI) citizen science monitoring project may provide additional knowledge of the distribution of this and other secretive nocturnal species. Roughly every 10 years, the UP and possibly the LP receive an influx of owls from the boreal forest of Canada when populations of snowshoe hares crash. The long-term viability in urban/suburban habitats is uncertain. Some suburban areas that had owls in the past do not have them today (Carpenter, unpublished) and, with the exception of Staten Island, they are not found in New York City (Eaton 1988). When it
© 2011 Kalamazoo Nature Center Great Horned Owl (Bubo virginianus) Thomas Carpenter
Literature Cited Conservation of Owls of the Northern Hemisphere; second international Blus, L.J. 1996. Effects of pesticides on owls symposium. U.S. Forest Service General in North America. Journal of Raptor Technical Report NC-190. St. Paul, MN. Research 30:198-206. Rohner, C., and C.J. Krebs. 1998. Responses Clark, A.J., and A.M. Scheuhammer. 2003. of Great Horned Owls to experimental “hot Lead poisoning in upland-foraging birds of spots” of snowshoe hare density. The Auk prey in Canada. Ecotoxicology 12:23-30. 115:694-705. Eaton, S.W. 1988. Great Horned Owl (Bubo Sauer, J.R., J.E. Hines, and J. Fallon. 2008. virginianus). In Andrle, R.F., and J.R. The North American breeding bird survey, Carroll, eds. The Atlas of Breeding Birds in results and analysis 1996-2007. Version New York State. Cornell University Press, 5.15.2008. USGS Patuxent Wildlife Ithaca. Research Center, Laurel, Maryland. Gancz, A.Y., I.K, Barker, R. Lindsay, A. Sheffield, S.R. 1997. Owls as biomonitors of Dibernardo, K. McKeever, and B. Hunter. environmental contamination. In Duncan, 2004. West Nile virus outbreak in North J.R., D.H. Johnson, and T.H. Nicholls, eds. American owls, Ontario, 2002. Emerging 1997. Biology and Conservation of Owls of Infectious Diseases 10:2135-2142. the Northern Hemisphere; second
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