Haven't been birding afield this weekend due to temporary termination of
tepid springtime but indulged in the armchair variety, poring through
a favorite book, "The Complete Falconer" by Frank L. Beebe, who appears to be a
North American guru of falconry, and he's not bad at depicting the subject with
pen & ink and paint brush either. The style of his paintings,
particularly those of raptors on the wing, remind my untrained and inartistic
mind of those in Penny Olsen's "Spirit of the Wedge-Tailed Eagle - The art
of Humphrey Price-Jones."
However, Beebe puts forth an astonishing hypothesis insomuch (if
I'm reading him correctly) he maintains DDT had no affect on Peregrine
populations. Rachael Carson would have had a fit. Anyhow, for what it's worth,
his argument goes like this:
"1966-67-68 falcon population surveys were funded and fielded for the
Canadian Arctic and Pacific Coast, Alaska, Greenland, California and Baja
Peninsula. Micrometer shell-thickness measurements of pre-DDT eggs in private
and museum collections across North America were taken. The average shell
thickness was then calculated and used as a baseline against which post-DDT
eggshell thicknesses were measured."
"Birds' eggs in collections are not really preserved eggs; they are but
eggshells from which the real egg content has been forced out through a small
hole drilled in the shell, by means of air under pressure. [ Hey! I've known
that since I was a branchling.] I have prepared many museum egg specimens and I
know that only strong, heavy-shelled eggs survive this pressure-preparation
process. Therefore, there is a tendency for most eggshells in collections to
have greater than normal shell thickness."
"Against this biased baseline, it was predictable that post-DDT eggshells
would go on record as being thin-shelled Sure enough they were. All the falcon
populations surveyed were reported as declining or "precariously" close to
"catastrophic declines". All were reported as having broken eggs, or
thin-shelled eggs. All had high levels of DDT in fat samples or from brain
tissue of adult peregrines and in most eggs tested. The "imminent
crash" of the Arctic population was considered as a certainty. More than twenty
years later [now ~ 35 years ] this has still not occurred."
I'm happy to believe Beebe is correct on this last point And I understand
that the Peregrine is no longer on the endangered list in the States but don't
know about Canada, only a few decades ago I don't think they had a federal act
pertaining to endangered species. However, some sub species were lost in areas
of the U.S and populations replaced with birds from elsewhere. Still I wonder
how an ostensibly intelligent person like Beebe went down the path he did with
this issue. After all he was up against some fairly erudite scientific
opinion rather than a Greenpeace/Monkey-Wrench-Gang bunch of radical
owlhoots. Maybe he held shares in DuPont Chemicals.
John K. Layton.
