Monday, April 18, 2011

Spring migration of White-breasted Nuthatch

adult female White-breasted Nuthatch
The familiar White-breasted Nuthatch is generally a resident species, with only some northern and western populations undertaking some migratory movements in some years (Grubb & Pravosudov 2008). On Sandy Hook, I've been told by many local birders many times over, the Red-breasted Nuthatch is usually easier to find, and some consider White-breasted Nuthatch "actually a reasonably good bird to get on the Hook". But where I do most of my Sandy Hook birding, i.e. on the northern tip, I always see more White-breasted than Red-breasted Nuthatches. Usually not more than one or two, though, and certainly not every day.

Today, however, migrant "WB Nuts" were everywhere, and I tallied a total of 30 individuals flying past the platform, all headed to the very northwestern tip of the Hook. Several landed in the tree behind the observation deck, and one even landed briefly on the deck's information panel. The majority were tree-hopping. Others were higher, a few even at a considerable height. What would they do once they hit the northwestern tip and see all that water, I wondered? Would they turn around, like raptors often do? Or would they gain more altitude and just go for it? I never saw them come back, so I assumed most of them were actually making the crossing.

For such a familiar species, surprisingly little still is known about the White-breasted Nuthatch, particularly regarding seasonal distribution patterns. Irruptive fall movements have been noted; for example, nearly 300 individuals were tallied during the fall of 1968 at the Bake Oven Knob hawk watch in Pennsylvania - against only 53 in all previous fall seasons of 1961-1967 combined (Heintzelman and MacClay 1971, cited in Grubb & Pravosudov 2008).

Summarizing this and other largely anecdotal accounts - all from fall seasons - Grubb & Pravodusov (2008) theorize that these movements possibly consist of juveniles, which they feel would explain why there is "little evidence of a return spring migration in this species".

Ron Pittaway's Winter Finch Forecast 2010-2011 mentions the Red-breasted Nuthatch's latest irruption, which was well underway by late summer 2010, but doesn't talk about the WB Nut.

eBird's monthly maps do not reveal a spring migratory pattern either.

Several birders who came up the platform today mentioned they had found multiple WB Nuts while birding the Hook for morning songbirds. So it wasn't like the same three birds were flying circles around the hawk platform, there was actual movement, noted by multiple observers. Detected movement was strongest during the first two hours of the count (between 8 and 10 EDT) but went on until late morning, early afternoon.

So where did today's birds come from? And where are they going?

Cited literature:
Grubb, Jr., T. C. and V. V. Pravosudov. 2008. White-breasted Nuthatch (Sitta carolinensis), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online:
Pittaway, R. (2010) "Ron Pittaway's Winter Finch Forecast 2010-2011", published on eBird's web site

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