I monitored night flight calls on a coastal headland for two autumn seasons,
2013 and 2015, using the same methods and equipment in each year. You can
see a summary table of the results here:
There was a remarkable increase in the number of warbler night flight calls
in 2015 compared to 2013. While many warblers increased 2 to 7-fold, Cape
May Warblers were 9 times higher and Bay-breasted Warblers 11 times higher.
The latter two species are known to be Spruce Budworm dependent species and
have been shown to increase substantially more than other warbler species
during an outbreak. There is reported to be an increasing infestation in
areas well north of my monitoring station. A possible cause for concern is
that another budworm dependent species, the Tennessee Warbler had fewer
flight calls in 2015.
Part of the reason for this post is to suggest that there can be a utility
to identifying difficult flight calls, like the zeep and double-up calls, to
the species level. Of course, these identifications are not going to be
correct all of the time. There is only a certain probability that they are
correct. I do use measurements and certain rules in guiding my
identification of difficult species. I only id to the species level when I
judge there to be a relatively high probability that it is correct, although
I can't as yet give an exact probability range. For those ids that I judge
to have less than a high probability, I leave to the generic or family level
(these are also listed in the table of results in this study).
Any comments would be most welcome.
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