Although the age of first breeding by Cooper's Hawks is often given as 2 years of age, published data indicates that one year old females and males often nest. The following is from: Curtis, Odette E., R. N. Rosenfield and J. Bielefeldt. 2006. Cooper's Hawk (Accipiter cooperii), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: http://bna.birds.cornell.edu.bnaproxy.birds.cornell.edu/bna/species/075 doi:10.2173/bna.75
They state: Age At First Breeding Usually 2 yr but year-old immatures reported as 6% to 22% of breeding females (Meng 1951, Hennessey 1978, Reynolds and Wight 1978, Millsap 1981, Moore and Henny 1984, Asay 1987). Those studies detected no males nesting as immatures but two such cases given by Rosenfield and Wilde (1982); similar proportions of yearling breeders in both sexes in Wisconsin, 1980–1992 (RNR and JB). Also, in Tuscon, AZ, where pairing was assorted by age, 83% of pairings were adults, 13% were mixed and 5% were subadults (N = 184, Boal 2001b); 16% of breeding females and 7% of breeding males were subadults. A pair of subadults successfully nested in Indiana (Dancey 1993), Wisconsin (RNR and JB) and New York (Rothstein 1993). Doug Kibbe, Littleton Date: Thu, 12 May 2016 22:34:33 -0700 From: [email protected] To: [email protected] Subject: [cobirds] Re: Immature Cooper's or Sharpie? - Larimer I plan on returning tomorrow in hope that a mate will appear. Perhaps that will solve the mystery... On Thursday, May 12, 2016 at 7:34:44 AM UTC-6, Gregg Somermeyer wrote:Late yesterday I spent some time observing what I believe to be either an immature Cooper's Hawk or Sharp-shinned Hawk on stick nest about 20 ft up in crotch of tree. Yellow eye, yellow and black beak, buffy head, barred tail. Is this possible? How old are they when they first breed? Gregg Somermeyer, Ft. Collins -- You received this message because you are subscribed to the Google Groups "Colorado Birds" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/cobirds/51a1e8f1-db94-4065-9a7b-890dbf9c7b03%40googlegroups.com. For more options, visit https://groups.google.com/d/optout. -- You received this message because you are subscribed to the Google Groups "Colorado Birds" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/cobirds/BLU174-W523EF06EB0362EA820AD84B6740%40phx.gbl. For more options, visit https://groups.google.com/d/optout.
