[obol] Peregrine Feeding
- From: Range Bayer <range.bayer@xxxxxxxxx>
- To: Oregon Birders OnLine <obol@xxxxxxxxxxxxx>, "Lincoln Co. Birding & Nature Observing" <LCBNO@xxxxxxxxxxxxxxx>
- Date: Wed, 2 Apr 2014 21:44:36 -0700
Passing this on for Michael McMann
---------- Forwarded message ----------
From: Mike McMann <mdmcmann99@xxxxxxxxx>
Date: Sun, Mar 30, 2014 at 4:52 PM
Subject: peregrine feeding
To: Range Bayer <range.bayer@xxxxxxxxx>
Hi Range, Checking back through some of the OBOL postings to catch up
and found Wayne's great observations on the peregrine that hauled a
male Surf Scoter up to the Yaquina Head cliffs. Don't have my
vacation sign-on completely figured out yet but was hoping you could
pass this on.
I'm a former falconer and have observed many Peregrine Falcons at
their eyries. This subject intrigues me and I thought others might be
interested in some observations and subsequent reading:
1) The 1/3 Guide Line: Brown and Amadon, 'Eagles, Hawks and Falcons of
the World' 1968, and others, use the 33% rule. That a raptor can
navigate comfortably with prey weighing 1/3rd of it's body weight in
most wind conditions. Wayne was surprised to find that the male Surf
Scoter weighed more than the Peregrine. I can only assume that he was
using Sibley's weights: Surf Scoter = 2.1lb. and Peregrine = 1.6lb.
Sibley apparently averages the weights for birds if there is a male
female difference. But there is as much as a 30-40% difference between
male and female raptors and between subspecies. John K. Terres, 'The
Encyclopedia of North American Birds,' 1995; site female Peale's
Peregrines (subspecies on Pacific Coast) as large as 3.5lb- largest
subspecies in the world.
2) Who's Doing the Hunting? Since there is such a difference in
weights between male and female Peregrines the prey weight will depend
on which is doing the hunting. Observers know that the female
peregrine does most of the incubation and feeding during early
nesting. That means the male is doing most, if not all, the hunting
and gathering during this period. With their weights varying between
1.8 and 2.33lb that means the prey normally has to weigh in between .6
and .8lb. Note: I led excursions where we assumed Rhinocerous Auklets
(1.1lb) were the main prey in one area. We never saw a single
Peregrine until we moved into a zone that featured an abundance of
Cassin's Auklets (6 oz.- .4lb.)
3) Wayne's Big Haul: This was undoubtedly an above average haul for
this Peregrine. Even if the Yaquina bird is one of the largest
Peale's Peregrines, a male Surf Scoter would have been 2/3 of it's
body weight. This is pretty far south for the Peale's subspecies so
if it is actually the smaller F. p. anatum subspecies it ups the ante
even more. I suspect Alan Jenkins is right (a USAF pilot would know a
lot about this) that the prevailing winds were favorable for this
female. It implies that the falcons can adjust their prey selection
if the wind is right...? Wondering also if this impressive kill was
part of a mating prenuptial given Wayne's further observations? Could
be the germ for a couple academic papers on the horizon...
Michael McMann
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