Winds diminished significantly last night, allowing for a good wave of songbirds to move into the area. Jeannette had at least 25 Hermit Thrushes at Hedgehog Mountain Park, while I had lots of activity at Portland’s Dragon Field: 31 Savannah Sparrows, 17 Yellow-rumped Warblers, 8 White-throated Sparrows, 6 Palm Warblers, 6 Pine Warblers, and 3 Blue-headed Vireos. (And, the Savannah Sparrows here at the store have departed).

A Fish Crow flew over, giving its diagnostic nasal call - a long-overdue (there's a colony not far away in Falmouth Foreside) addition to my Dragon Field list that now stands at 144 species. My goal is to “finish” the patch list (reach 150) by the end of this year – and my work is really cut out for me! I have no easy birds left; it’s just a matter of luck now. Missing that Northern Shrike this winter, and the Red-bellied Woodpecker last fall, may come back to haunt me! I need some uncommon migrants, like Red-shouldered Hawk and Mourning Warbler, but I’ll need a couple of rarities – or some really dumb luck (like a new flyover shorebird or duck) to reach the target.

Also at Dragon Field today, I once again saw a Gray Catbird that has been present there since late last fall. We’re still 1-2 weeks away from newly arriving migrant catbirds, but thanks to the mild winter this bird is already set up on territory -saving himself (I have heard it sing, so it is a male) the arduous and dangerous journey of thousands of miles of migration.

There’s no way of knowing why he stuck around last fall. An injury? Was he unable to build up enough fat reserves? Was he just stupid? No matter what the reason, the mild winter – and a good fruit crop last summer/fall – allowed him to survive.

For sake of argument here, let’s say that this catbird's failure to migration was casued by a genetic defect. A severe (normal?) winter would have eliminated his genes from the gene pool. However, if that defective gene prevented him from migrating (such as disrupting the hormonal change that triggers migration tendencies) allowed him to survive (i.e. provides a benefit in terms of fitness – such as not flying into a communications tower while migrating one night), that gene will be passed on to his offspring. Furthermore, since he is already on territory, he has the “home field advantage” when a newly returning migrant that has just flown in from Belize shows up. Now, let’s say that this gene prevents his offspring from migrating next fall. Next winter is also mild – continuing the long-term trend of mild winters due to global warming – and the whole family survives. And the same thing in the next year. Alas, a population of non-migratory Catbirds develop and begins wintering in Maine.

Now, this is a complete hypothetical - and greatly oversimplified scenario – but it’s a useful example of how some species adapt to changing conditions (unfortunately, we don’t seem to be seeing many species that are adapting positively to the extremely rapid changes caused by the Global Climate Change that we are now witnessing). Evolution in action at Portland’s Dragon Field? Or, just one darn lucky little catbird!