Hi, Dave -
I was in the process of writing a reply when I got Doug's response. He did a
better job than I was doing. I would like to add two clarifications.
1. As Doug indicated, "It is hard to demonstrate assortative mating in the
field." However genetic studies have shown that in multiple regions of North
America, 2 or more types of crossbills coexist whose genomes show evidence that
they have not interbred with each other to any great extent recently. This
conclusion, originally reached by Jeff Groth, was a big surprise. It was
essentially data-driven, rather than theory-driven science.
2. Doug is correct that only the Cassia Crossbill has been split, but another
reason has held up the splitting of more. Determination of which scientific
names are "correct" for which taxa is with a few exceptions determined by date
of the first description that applied a Latin name to a particular species. In
many cases two or more different authors coined names for what was later
decided was the same species. The correct name is then supposed to be the one
that was coined first, provided that the description or other evidence (ideally
a type specimen) is clearly of that species. Many old bird scientific names
are based on paintings of the birds, and this is often adequate to establish
what species that name belongs to. However in the case of crossbills, where
multiple old names exist, it has been extremely difficult to determine which
"types" were responsible for which descriptions or for which paintings. The
Cassia Crossbill could be split because it has a limited range, and no previous
crossbill Latin names had been coined from birds from that area.
Wayne
On 1/19/2018 5:24:27 PM, W. Douglas Robinson <w.douglas.robinson@xxxxxxxxx>
wrote:
Dave,
If you search scholar.google.com for Red Crossbill, I think you will find links
to dozens of research articles, many of which are based on both observation and
experiment. The work from Craig Benkman and his colleagues is especially strong
and insightful.
Crossbills are difficult to study. That is why only Cassia Crossbill in North
America has been split. It is hard to demonstrate assortative mating in the
field. The other types are not known in sufficient detail to demonstrate
limited gene flow; yet. That is part of what makes crossbills a fun problem to
solve. How many cryptic species might there be? None? One more? 10 more?
I am unaware of any evidence that individual crossbills ever utter more than
one flight call type. I think we can feel good that, if it happens, it is rare,
based on thousands of hours of observation and hundreds of recordings.
It is obvious that most crossbills eat more than one species of conifer seed.
There are at least 5 types eating Sitka Spruce on the Oregon Coast now. All of
those except type 10 are thought to specialize on other species besides Sitka.
Specialization does not mean exclusivity. There is good scientific data showing
that bill morphology influences efficiency of seed extraction depending on the
match of cone morphology and bill size and shape. One can eat food from other
crops even though one is not very efficient at it. You can eat nectar from
honeysuckle if you’re in a pinch but hummingbirds are obviously far more
efficient at it.
This is a well studied group of birds yet we still have much to learn.
Doug
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