Sharp-shinned Hawk (Accipiter striatus) Gerald R. Urquhart
Missouri. 4/21/2009 © Elizabeth Rogers (Click to view a comparison of Atlas I to II)
The small, acrobatic Sharp-shinned Hawk is an relatively stable numbers in the NLP, with 16.95% for MBBA I and 13.95% for MBBA II, abundant migrant but an uncommon breeder in and in UP townships with 21.80% in MBBA I Michigan. During migration they funnel into and 21.26% in MBBA II. Because of their points that concentrate migrant songbirds and small size and secrecy during the nesting patrol like squadrons of biplanes, dropping from season, confirmed breeding was recorded in less above to ambush prey up to the size of Blue than 1% of townships (17 of 1,925). The Jays. In the breeding season, they disappear increase in SLP breeding may be due to into woodlands where they use their long tails maturation of forests. Ontario had a substantial and short wings to pursue prey through even the increase in observations in their Carolinian densest of vegetation. forest region (similar to our SLP forests in
species composition, level of fragmentation, and Sharp-shinned Hawks range from Alaska and age of stands) from their first atlas with 7.9% of Labrador south to Argentina, with several blocks occupied (Cadman et al. 1987) to 33.8% subspecies being endemic to Caribbean Islands. in the second atlas (Gahbauer 2007). The main North American subspecies, A. striatus velox, breeds over most of Canada and In Wisconsin, the highest concentration of the northern U.S., with densities becoming breeding records comes from the northern third lower in the Southwestern U.S. and Appalachian of the state (Jacobs 2006). States to the south region. had very few breeding records, with sparse
populations in east-central Ohio (Austing 1991) Distribution and southern Indiana (Squires et al. 1998), and In Michigan, the Sharp-shinned Hawk breeds in only a few scattered records in Illinois (Walters both the UP and LP, but their highly secretive 2004). nature during breeding resulted in few records to clearly define their range. The results from Breeding Biology MBBA I and MBBA II show a substantial Relatively little is known of the breeding increase in SLP townships with breeding behavior of Sharp-shinned Hawks in Michigan evidence from 6.03% in MBBA I to 11.71% in because of their highly secretive nature. MBBA II. Breeding evidence suggests
© 2011 Kalamazoo Nature Center Sharp-shinned Hawk (Accipiter striatus) Gerald R. Urquhart
Although some birds overwinter sparsely in Hawks nested more frequently in coniferous and Michigan, most of the individuals that breed in mixed forests than Cooper’s Hawks, as well as Michigan probably winter in the southern U.S. forests with larger trees. and return to the breeding ground in April. Abundance and Population Trends Nesting takes place in coniferous, deciduous, As common as Sharp-shinned Hawks are during and mixed woodlands with most nests found in migration, actual population numbers are conifers (pine, spruce, tamarack and cedar) difficult to determine. Few observations of (Barrows 1912). The broad, flat nests are nesting birds and a lack of nest surveys in located from 12 to 55 feet above the ground, and Michigan make any trends in population are made of dead twigs and bark, measuring 35- difficult to discern (Betz 1991). Although 60 cm wide and 10-14 cm deep, nearly the same breeding survey block numbers do not dimensions as the larger Cooper’s Hawk necessarily reflect population changes, there (Barrows 1912, Bent 1937). was a sizeable increase in the number of blocks Females lay individual eggs on alternating days with breeding evidence between MBBA I and with four to five eggs (range three to eight) in a MBBA II in the SLP, possibly tied to clutch, and only a single clutch laid each year maturation of old fields into forests in the SLP. (Bildstein and Meyer 2000). Most estimates of Combined historical breeding bird survey data incubation period range from 30-35 days, with show no significant trends for Michigan or the the eggs all hatching within 48 hours, Midwest between 1966 and 2007 (Sauer et al. suggesting delayed onset of incubation (Palmer 2008). 1988). Migration counts are one of the best indicators Accipiters have a high degree of sexual of population, but inter-annual variation makes dimorphism, with male Sharp-shinned Hawks it difficult to determine trends and causes significantly smaller (24-27 cm) than females (Farmer et al. 2007). Michigan’s two hawk (29-34 cm) and weighing only half as much as counts with the longest coverage are mostly females in many cases (Wheeler and Clark surveying birds that breed in Ontario, but both 1995). The altricial hatchlings rapidly have shown decreases in Sharp-shinned Hawks differentiate in size, with females gaining mass in recent years. The Southeastern Michigan faster but more slowly developing plumage. Raptor Research data (Wayne County) from Males develop plumage, flight skills, and fledge 1999-2008 indicate an average decrease in up to several days before females. Birds migrating Sharp-shinned Hawks of 9% per year fledged between 21 and 27 days in U.S. during this period, although there is high annual populations, and young remained with parents variability (HMANA 2009a, 2009b), and for approximately 3.5 weeks after fledging Whitefish Point Bird Observatory had a (Bildstein and Meyer 2000). declining trend from 1979-2007 (RPI 2010). Although discrete data for Michigan-breeding Sharp-shinned Hawks are often thought of as Sharp-shinned Hawks are unavailable, regional smaller versions of Cooper’s Hawks, but trends all indicate a decrease in migrant birds. difference in distribution and habitat choice During the 1980s and early 1990s, similar exist (Trexel et al. 1999). Cooper’s Hawks declines in migratory numbers occurred in the breed throughout the United States and Canada, Eastern U.S. (Viverette et al. 1996), and Wood but Sharp-shinned Hawks are much more et al. (1996) suggested that these may be due to common in the northern U.S. and Canada. more Sharp-shinned Hawks wintering Trexel et al. (1999) found that Sharp-shinned
© 2011 Kalamazoo Nature Center Sharp-shinned Hawk (Accipiter striatus) Gerald R. Urquhart northward, but also noted that environmental Cadman, M.D., P.F.J. Eagles, and F.M. contaminants may play a role in the decline. Helleiner. 1987. Atlas of the Breeding Birds of Ontario. University of Waterloo Conservation Needs Press. Waterloo, Ontario. At first glance, Sharp-shinned Hawk Farmer, C.J., D.J.T. Hussell, and D. Mizrahi. populations appear to be relatively healthy in 2007. Detecting Population Trends in North America because of their abundance in Migratory Birds of Prey. The Auk 124:1047- migration, but declines in migratory numbers 1062. raise some concern. Because they feed almost Gahbauer, M.A. 2007. Sharp-shinned Hawk exclusively on birds, their populations are (Accipiter striatus). In Cadman, M.D., D.A. vulnerable to environmental problems that Sutherland, G.G. Beck, D. Lepage, and A.R. impact forest dwelling birds, many of which are Couturier. 2007. Atlas of the Breeding Birds Neotropical migrants. The trends observed at of Ontario, 2001-2005. Bird Studies migration points may simply indicate a change Canada, Environment Canada, Ontario Field in migratory behavior rather than populations Ornithologists, Ontario Ministry of Natural (Viverette et al. 1996), but they warrant further Resources, and Ontario Nature. Toronto, monitoring. Research should be done to Ontario. correlate decreased migration numbers and CBC Hawk Migration Association of North America data to determine whether the declines are (HMANA). 2009a. Hawkcount for Detroit resulting from reduced migration or from an River Hawk Watch, Point Mouillee State actual population decrease. Game Area.
© 2011 Kalamazoo Nature Center Sharp-shinned Hawk (Accipiter striatus) Gerald R. Urquhart
Squires, B., J.S. Castrale, and C.E. Keller. 1998. Suggested Citation Sharp-shinned Hawk (Accipiter striatus). In Castrale, J.S., E.M. Hopkins, and C.E. Urquhart, G.R. 2010. Sharp-shinned Hawk Keller. 1998. Atlas of Breeding Birds of (Accipiter striatus).. In Chartier, A.T., J.J. Indiana. Indiana Department of Natural Baldy, and J.M. Brenneman (eds.). 2010. Resources, Division of Fish and Wildlife, The Second Michigan Breeding Bird Atlas. Nongame and Endangered Wildlife Kalamazoo Nature Center. Kalamazoo, MI. Program. Indianapolis, IN. Accessed online at:
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