Flora and Fauna News

Tropicals Birds
Heading Back

By Michael Plagens
Sonoran Desert Sciences

PINTO CREEK, Az ----- By mid-August, well before the Sonoran Desert's human residents become aware of any seasonal cooling, tropical birds that have spent the summer in the northern latitudes begin filtering through Arizona on their way back to Central and South America. Known as Neotropical Migrants, these tropical birds of the New World, have, over evolutionary time, discovered that there is a bounty of food during the brief summer of the Temperate North. But, they have retained their sensitivity to cold weather and its lack of available food and so must migrate back and forth each year.

Many kinds of birds fall into this category including tanagers, hummingbirds, flycatchers, swifts, swallows, thrushes, and cuckoos. Among the most diverse and colorful are the warblers. Although mostly quite small, they are conspicuously colored with yellows, oranges, reds, and blues. It's little wonder that warblers are a favorite with bird watchers. One common species now moving along Pinto Creek near Globe is Wilson's Warbler. The males are bright yellow with a dashing little black cap. Back in June they were busy rearing their young in the Northern Rockies as far north as Canada and are now headed to Southern Mexico, Costa Rica or maybe as far as Panama. Weighing in at barely 7 grams (less than ½ oz!) these high energy birds must stop frequently for fuel and water. For much of the arid southwest this means they must move within riparian corridors -- permanent waterways -- and they prefer those that are oriented north-and-south. Here the trees and plants are green and there are fruit, flower nectar, insects and spiders to eat.

If that weren't enough, Neotropical Migrants now face an increasingly difficult task in that more and more of these waterways are altered or even dried up as a result of human disturbance. The Santa Cruz River was once a vital waterway in the past that flowed from the Mexican Border to the Gila River. It is now almost always dry. The San Pedro River is still intact and vital, but is threatened by rapid population growth in Sierra Vista, Arizona. Pinto Creek in Gila County, as another example, has been subject to mining spills, overgrazing by cattle, and pollution from human habitations.

It is a wonder of nature that such tiny birds can navigate the gauntlet of difficulties across a 5000 km trek, twice each year. They bring vibrancy and beauty wherever they go. Hopefully, humans will be wise enough and diligent enough to prevent damage to the riparian habitats they require for their survival.

Yellow-breasted Chat (Icteria virens)
Photography by Robert Shanz