Those who doubt global climate change are, as far as I know, poorly represented among field biologists. We rather scruffy scientists (few of us are fashion plates) have seen major changes in fauna and flora during the last 50 years. In my own case, this has been especially evident in insect species, several of which have moved higher in mountains or further north (see butterflies and global warming) and in some plants, which have somewhat altered their blooming times (see blooming time and global warming). However, one should not attribute every change in distribution to global climate change. Organisms can change and have changed their distribution for other reasons. In the Southwest, the cases of the Common Crow, the Great-tailed Grackle and the White-winged Dove are instructive in this regard. The American Crow seems to have invaded the area in which I live from the north and Great-tailed Grackles and White-winged Dove from the south. The invasion of crows is within my tenure, but the doves and grackles were already here in numbers when I originally moved to New Mexico in 1978. After a year and a half back in Florida, starting in 1981, I returned in 1983. There were still no crows. By the 1990s there were some crows here during the winter and now there are thousands.
In checking my copy of "Birds of New Mexico" by Florence Merriam Bailey (published by the New Mexico Department of Game and Fish in 1928) I came up with the following quotes, first on the American Crow (referred to as the Western Crow by Bailey).
"On March 26, 1926, Ligon observed about 100 birds 3 miles south of Bernalillo, which as a rule represents about the southern limit of range on the Rio Grande."
Bernalillo is near Albuquerque. She also noted 3 birds seen 10 miles west of Elephant Butte Dam. Now in winter I cannot open the front door without hearing the familiar "caw, caw. caw." The flocks are everywhere!
As to the Great-tailed Grackle, Bailey notes
"Although rare in New Mexico, in Brownsville, A. P. Smith says, the Jackdaws are found 'in possession of the streets....' "
He is referring to Brownsville, Texas, and quite accurately, as during a visit I made there in the 1980s I got exactly the same impression. Jackdaw is another name for the Great-tailed Grackle, which was separated from the Floridian and eastern Gulf Coast Boat-tailed Grackle by modern ornithologists. She also says that a male was shot in Las Cruces in 1913. Again I can hardly take a walk without seeing these now ubiquitous birds. These were referred to as "trash birds" by a nature writer I know!
Male Great-tailed Grackle on Afghan pine in Mesilla Park, NM
White-winged Doves are now everywhere in the Rio Grande Vally, yet Bailey says
"From Mesilla, Professor Merrill reported 'I have noted this species only once, the summer of 1912' "
I once counted well over 400 perched on the power lines in Mesilla during the winter!
White-winged dove on clothes line in Mesilla Park, NM
What are we to make of one bird going south (American Crow) and two going north (Great-tailed grackle and White-winged Dove)? In truth none of these cases proves much about climate change, but instead these testify to the ability of some birds to take advantage of new opportunities (see expansion of white-winged dove range). All found new resources in modern agriculture and two of the birds (crow and grackle) are now considered major agricultural pests. They are routinely poisoned at the dairies and farmers have never liked them (poisoned birds). If it was not for their popularity with hunters, the doves would probably be in the same boat. I have seen them by the hundreds eating from cotton seed piles.
To show evidence that we can really ascribe to global climate change I now await the arrival of two more southern birds that are found as close as Tucson and are less likely to be influenced by agriculture - the Black Vulture and the Common Ground Dove!
The patterns caused by natural expansions of range by opportunistic biota (the Cattle Egret is another case obviously not, at least initially, climate change related) have to be separated from those resulting from the true effects of climate change and this is not always as easy as in the case of the three birds which are the subject of this diary. Add to this human caused range extensions, such as the introduction of Burmese Pythons, Walking Catfish, several species of parrots, the Nile Monitor and the Green Iguana to Florida, and you see a very complex picture of distributions. On the other hand the recent movement of the Brown Widow Spider north and west from Tampa, Florida, to Louisiana and Texas, and north and east in California may be one of those range expansions affected by global climate change (at least in part), and this may also be true of the further north push of the Cattle Egret and even the grackle and dove. References to most, if not all, of these can be found on the Internet. It's complicated!
All photographs are by me, taken in New Mexico over the last year or so. Crows, as I have discovered, are very difficult to photograph!