A recent thread on whether warblers migrate as a group, in same-sex
flocks, etc., got me browsing through some recent journals. One article
I found in the J. of Field Ornithology was

Wiedenfeld, D.A. and M.G. Wiedenfeld. 1995. Large kill of neotropical
migrants by tornado and storm in Louisiana, April 1993. J. Field
Ornithol. 66(1): 70-80.

Abstract. - A tornado and storm on 8 Apr. 1993 at Grand Isle, Louisiana
killed an estimated 40,000 birds of 45 species. The ten species killed
in greatest numbers accounted for about half of the birds killed.
Species of concern because of their already declining numbers included
the Wood Thrush (Hylocichla mustelina) and Cerulean (Dendroica cerulea)
and Swainson's Warblers (Limnothlypis swainsonii). This kill is the
largest one recorded on the Gulf of Mexico coast. It may have been so
severe because the storm occurred at the time of day when the greatest
number of birds was arriving at the coast after having migrated all night
northward across the Gulf.

In their discussion of finding birds washed up on the beaches they note:

"The differences in relative abundances of species, sexes and age classes
killed probably indicate that these groups migrate on different days, or
perhaps in groups of like individuals. Such differences are widely known
to ornithologists, but from the data here presented it is not possible to
rule out the possibility that different grups were able to survive the
storm differentially...

"We also have one bit of interesting anecdotal information regarding the
distribution of birds along the beaches. Early in our searches it was
our impression that species were clumped. That is, if we found one
Ovenbird, it was very likely that the next bird we found would also be an
Ovenbird, and we subsequently might not then find another one for a long
stretch of beach. Although this just may be a misperception, the only
two Chestnut-sided Warblers we found all day were within 13 m of one
another; both Yellow-billed Cuckoos we found were within about 30 m, and
all three Blue-winged Warblers were within 60 m. As these birds had died
at sea and drifted to shore, this would suggest that the birds had to
have gone into the water close together and at almost exactly the same
time. This lends credence to the idea that it was the tornado that
killed many of the birds, because the tornado is a very localized
phenomenon relative to the larger storm. This evidence also suggests
that birds of a single species or class migrate together in very close
flocks, as also proposed by Moore (1990)."

Moore, F.R. 1990. Prothonotory Warblers cross the Gulf of Mexico together.
J. Field Ornithol. 61:285-287.


One of these days, I hope that I have the chance to make it out East to
see the spring warbler migration. Until then, I guess I'll just have to
put up with the fantastic year-round birding available in the PNW.

Jon. Anderson
Olympia, WA
anderjda at dfw.wa.gov