While cleaning my office, looking for other articles I encounterned an
interesting paper on avian hybrids and species concepts: "Hybridization
of Bird Species" by Peter and Rosemary Grant, Princeton University.
[Science, vol. 256, pp. 193-197, 10 April 1992] In the introduction they
survey literature on number of bird species that have produced
recognizable hybrids in the wild, with support for a number around 10%.
The have a handy table of known hybrids arranged by order, supporting
what some had said earlier-ducks and geese seem very prone to
hybridization (or at least producing visible hybrids)-In Anseriformes 42%
of species have had hybrid progeny observed. Other groups, such as
swifts, have no known hybrids. In their data, they observed cohorts of
Darwin's finches on the island of Daphne Major. During their survery
period of several years in the 1980's, they found that the resident
spedcies of finches produced rare(1-2%) but regular numbers of hydrid
offspring. On following these young, they found that they were just as
fertile and had higher survival rates than the two parent species. This
kind of observation is a good example of the difficulty of defining
species.

The authors also raise two other interesting notions in the discussion.
First, these results need to be looked at during multiple stages of
weather-climate cycles; this advantage of hybrids under current climate
may not always hold true. Also, recognizing that hybrid production and
backcrossing may be a fairly common part of the natural history of some
organisms, such as many orders of birds, emphasizes the omission of
hybrid species from the US endangered species act. As these authors
point out, rarity may well increase the rate of hybrid production, due to
difficulty in finding a conspecific mate. The species most in need of
protection are the most likely to lose it by this mechanism.

This raises a related question that I have seen in the popular media for
a while but have not seen much on lately: one of the concerns in the
spotted owl conservation plans was the "swamping out" of spotted owls by
direct competion and hyridization with barred owls. The Grant and Grant
paper indicates that owl hybrids are rather rare (or at least not easily
recognizabel), with less than 1% of the known species producing hybrids.
I do remember seeing some notes on owls that were apparently
barredXspotted owl crosses. Can anyone update me or expand on what
poeple know about this particular hybrid example?

PS-this find is an example of why I will never give up hard copies of
magazines and go the the paperless, internet forum of the future, or at
least be dragged in kicking and screaming. Some of my favorite articles
are things I have found while looking for somthing else.

Jim Neitzel
The Evergreen State College
neitzelj at elwha.evergreen.edu