What was done
In addition to examining pertinent data in the literature, the authors conducted a three-year field study on ranch land of the Welder Wildlife Refuge along a 30-km stretch of the Aransas River in southeastern Texas, which they say is located "at the northern end of the New World subtropics," in an attempt to determine to what extent tropical and subtropical birds from lower latitudes may have been making their way northwards in response to regional warming since the mid-1970s.

What was learned
In the words of the five U.S. researchers, "range change is occurring at a rapid rate for tropical, subtropical, and warm desert birds in Texas." More specifically, they report that "comparisons between former (1974) and current avian distributions for the region show significant breeding range extension of 40-220 km to the north, northeast or east for at least 68 species, many of which cross major biogeographic boundaries." As for the driving force or forces behind these range extensions, they conclude that "change in key parameters of habitat, e.g. seasonal food availability, as affected by factors related to climate change, e.g. mean annual precipitation, temporal distribution of precipitation (monthly means), or monthly means for nighttime-low temperatures during the breeding season, provide the most likely explanations for observed range extensions."

As for the single overriding "environmental factor associated with avian range shift in South Texas," Rappole et al. identify "change in mean annual temperature," as documented by Norwine and John (2007). And as an important added bonus, they report that the movement of this "large segment of the subtropical avian community into temperate habitats has not been met with a corresponding shift of temperate species as had been predicted by a number of models." Quite to the contrary, as they continue, "the communities now overlap, creating, in effect, novel communities." And these new communities possess a greater biodiversity than the ones that existed there prior to the arrival of the many new tropical and subtropical bird species.

What it means
Whereas climate alarmists see little of hope in warming-induced migrations of species - see our Major Report The Specter of Species Extinction: Will Global Warming Decimate Earth's Biosphere? in our Education Center - real-world studies paint a much different picture of the recent and ongoing reorganization of the planet's many and varied ecosystems.

Reference
Norwine, J. and John, K. 2007. Welcome to the Anthropocene: South Texas climate. In: Norwine, J. and John, K. (Eds.). The Changing Climate of South Texas: 1900-2100. Texas A & M University, Kingsville, Texas, USA, pp. 1.4.