Monday, April 11, 2005

Blakeman answers Watson:More on the Hawk Size Muddle

I'll ask the question quite a few readers may be wondering about: What exactly are the vertebrate/invertebrate generalists? I suppose these are hawks that eat insects and worms as well as meadow voles---like screech owls. Am I right? Other species of hawks or owls in this category?

Marie and Steve,
Yes, I've read Dr. Tom Cade's work on this (many years ago), but I don't have it at hand, and I don't think it much resolved the "why" of reverse sexual dimorphism in raptors, although it tended to carefully quantify the "what" of the question. I'll leave it to someone else who has more closely followed modern research developments to give a contemporary explanation of reverse sexual dimorphism in raptors.
[For those new here, virtually all raptors, both in owls nocturnally and in all diurnal raptors, hawks, falcons, eagles, others, females are larger than males, and females do most of the incubating. Why this is so remains a contentious question. In most other avian species, males are larger, but not in raptors. Why? A big question.]
Steve, I understand (as I'm sure you do, too) the correlation coefficient numbers. The -0.209 is most interesting, indicating that for this group of raptors ("vertebrate/invertebrate generalists") there is actually a very slight negative correlation between female sex and size. Makes sense, as most hawks in this category are smallish species. The other two categories are pretty significant.
Remember, a 0.0 correlation datum means that one quantity is totally unconnected to some other. One event or trait or characteristic has absolutely no connection to the other one. In the case of a -1.0 correlation, one datum is absolutely, 100% oppositely connected to the other. When one thing happens or occurs, the other never, ever does. Conversely, a 1.0 correlation means that when one thing or event occurs, another one must also always occur.
So, the 0.4 correlations of the other two categories are very strong. But again, the specific "why" of these correlations is contentious. I hope a more knowledgeable viewer could bring us up to date on this. I appreciate, Steve, that you have taken the time to sift through some of the more modern papers on the subject. Sadly, since I'm not in a university town, I don't have access to modern ornithological journals, so I'm nothing of an expert on the topic. I'm aware of its difficulties, but not of any recent resolutions of the problem.
And I thank you for your kind attribution of my Ph.D. But sadly, it's figmentary. I'm just Mr. Blakeman, a retired advanced placement biology instructor, now doing native plants landscape designs and installations. I defer to authentic Doctors of Philosophy. My expertise derives mostly from extensive hands-on field studies of red-tails, not from properly attained higher degrees or published papers.
John A. Blakeman