Red-breasted nuthatches stage incursions into Ohio on a fairly regular
biennial schedule.  In recent decades, seed crops at higher latitudes
have peaked in the odd-numbered years (many trees show increased
production of fruit every other year--even many of our oaks, producing a
similar rhythm in winter reports of red-headed woodpeckers). Good crops
promote higher populations of nuthatches, and hence noticeably more
birds moving south in the following autumn. These incursions usually
become evident by August, when we start seeing a lot more nuthatches
than the previous year.
        In Fall 2005, the Ohio Cardinal reported: "A marked incursion. R. Royse
reported 18 Oct that all hemlock groves and some pine groves in Shawnee
SF harbored this species. The 10 Sep CVNP census had 44 red-breasteds to
100 white-breasteds. The southwestern counties contributed 40 reports of
this species during the period."  In 2003 it was "Obeying its apparent
biennial cycle, numbers were up. Multiple sightings included 10 at the
CVNP 13 Sep (L. Rosche), seven at Winton Wds 21 Oct (F. Renfrow), five
at Secrest Arboretum in Wayne 8 Nov (S. Snyder), and three at Findlay SP
in Lorain 22 Nov (C. Rieker). And in 2001: "Early sightings can presage
invasions by northern birds, as in 1995, when early Sept nuthatches were
followed by higher than usual numbers of redpolls, siskins, and evening
grosbeaks; appearances of nuthatches as early as 15 Aug in 1993 were
followed by flushes of the same species. This year Aug sightings began
on 13 Aug in Cuyahoga (S. Wright), two in Lake on 23 Aug (J. Pogacnik),
and five in Cincinnati on the 29th (D. Brinkman). Later, the CVNP census
counted 36 on 15 Sept, and B. Zwiebel had ~20 at Magee on 7 Oct."
        These regular odd-numbered-year irruptions are not ironclad
certainties, of course. The fall of 2004 had more r-b nuthatches than
usual too, with some good records. But overall, the biennial hypothesis
usually comes through: long-term Ohio numbers from Christmas Bird Counts
and from venerable journals like the Cleveland Bird Calendar seem to
reflect it overall. At this point, 2007 seems to be following the pattern.
        Nuthatches seem to be the most susceptible to periodical irruptions,
though lots of other high-latitude seed-eating birds show some
regularity: siskins, redpolls, grosbeaks, even chickadees and waxwings.
We'll see about the other ones later, but for now it looks good for
another nuthatch incursion.
Bill Whan
Columbus

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