Autumn raptor banding at Hawk Ridge, Duluth, Minnesota U.S.A., 19722009: An overview

We summarize autumn banding of 99505 raptors (mean of 2619/yr) of 23 species at Hawk Ridge from 1972 to 2009. Excluding the first two years of banding (1972 and 1973) and despite consistent effort, the last six years (200409) were six of the seven lowest totals banded over a 36-yr period, primarily due to the low number of Sharp-shinned Hawks (Accipiter striatus). The majority of birds banded were Sharp-shinned Hawks (n = 60147) and Northern Saw-whet Owls (Aegolius acadicus; n = 20676). The totals also included 8103 Northern Goshawks (Accipiter gentilis), 2243 Long-eared Owls (Asio otus), and 92 Boreal Owls (Aegolius funereus). Numbers of Northern Goshawks banded at Hawk Ridge were correlated with raw counts (r = 0.68, P < 0.01) and effort-adjusted counts (r = 0.59, P < 0.01) observed at Hawk Ridge. Sharp-shinned Hawk counts when effort was included were correlated with the number banded (r = 0.58, P < 0.01). Three species have had a substantial number of encounters (any handling of a banded bird, alive or dead) and returns (first recapture of a banded bird at or near the site of banding at a different season of the year). These included 462 Northern Saw-whet Owls (n = 330 encounters and 132 returns), 388 Sharp-shinned Hawks (n = 327 encounters and 61 returns), and 280 Northern Goshawk (n = 230 encounters and 50 returns). Age ratios of Sharp-shinned Hawks, Northern Goshawks, and Northern Saw-whet Owls were highly variable, but ratios of hatch-year to after-hatch-year birds were negatively correlated (r = -0.40, P < 0.01) with the number of Northern Goshawks banded. Adult Northern Goshawks dominated peak years of Northern Goshawks, whereas hatch-year birds dominated when numbers were low.