"Birds are an ecological litmus paper." — Roger Tory Peterson

Since the beginning of life on earth four major groups of creatures independently evolved wings for self-powered flight (not just gliding). First there were insects. About 385 million years ago the first insects show up in the fossil record. However, they were scarce until about 325 million years ago. What happened? Several groups of insects evolved wings and the number of insect species “exploded.”

One group, the Meganeura, lived some 300 million years ago, were likely precursors of dragonflies and had wingspans of up to 70 cm (about a yard). Next came the reptiles, pterodactyls or pterosaurs to be more precise, which lived somewhere around 228 – 66 million years ago. At least 130 genera have been identified, with numerous species within each genus. Their wingspans ranged from 25 cm to 11 m. Often mistakenly said to be dinosaurs, pterosaurs lacked the skeletal features that characterize dinosaurs (legs and arms perpendicular to their spines giving them two or four appendages in contact with the ground for locomotion) and so have been classed as reptiles whose arms and legs (if they have arms and legs) splay out laterally from their backbones.

The next group to take flight were dinosaurs, about 150 million years ago. These were an offshoot of therapod dinosaurs, close cousins of Velociraptors and Tyrannosaurus rex. Unlike most dinosaurs that went extinct about 66 million years ago when a huge asteroid slammed into earth off the coast of Mexico near the Yucatan Peninsula, this group survived. Today we call them birds. The final group to take to the skies were mammals. Bats show up in the fossil record about 50 million years ago, a geological “blink of an eye” since that asteroid hit our planet. Today there are over 1,400 species of bats, ranging from bee-sized to the largest having wingspans of 1 m. Adapting to flight, whether insects, pterosaurs, birds, or bats, has allowed those groups to radiate into many species. Rather than being stuck to a land-bound, two-dimensional niche, these species are able to exploit a third dimension and in doing so, proliferate.

There are currently about 10,000 species of birds on earth, occupying every continent — including Antarctica. Flight has enabled many birds to migrate vast distances, taking advantage of seasonal abundances in food, and then quickly escape when that food becomes scarce. Still, there are some birds that call our desert home all year long. Many more have moved in to exploit suburban habitats and some of those are uncommon true desert denizens but are abundant in suburban yards. Those suburban entrepreneurs include roadrunners, mockingbirds, house finches, Bewick’s wrens, mourning doves, Cooper’s hawks, American kestrels, and Costa’s hummingbirds. Most of these can be found away from suburbia living a desert life year-round, but they are uncommon, whereas in suburbia they have become far more than common place.

Then there are year-round desert birds that either eschew suburbia, or at best only occasionally enter the world of stucco walls and swimming pools. Those include black-throated sparrows, arguably the most beautiful of North American sparrows, rock wrens, canyon wrens, cactus wrens, northern shrikes, ladder-backed woodpeckers, Say’s phoebes, horned larks, and verdins. It may seem odd to have a true desert woodpecker, often living where trees are absent or rare. In those treeless expanses ladder-backed woodpeckers will excavate nest cavities in the plumper stalks of agaves and yuccas, and forage on fat beetle larvae munching their way through those same stalks.

Of course, we have our “snowbirds," both feathered and human, that enjoy the relatively mild winter desert climate only to escape northward as soon as the temperatures rise toward the century mark. Those feathered snowbirds include white-crowned sparrows, phainopepla (migrating coastward rather than northward), Bell’s sparrows, northern flickers, Brewer’s sparrows, and yellow-rumped warblers (“butter butts”). Phainopeplas are the only ones on this list that breed here in the desert. Then amazingly they migrate to the coastal oak woodlands and breed again, the only bird known to breed in two separate habitats each year. Incongruously, we also have the opposite of snowbirds, species that winter further south and then migrate to our desert to breed in those plus century mark summers. Ash-throated flycatchers, Scott’s orioles, and white-winged doves fall into this group.

There are also birds without any specific habitat preferences, often top of the food web and ecologically referred to as “generalists." Ravens, crows, red-tailed hawks, prairie falcons, barn owls, great horned owls all fall into this category. Another addition here could be burrowing owls, although they could be easily classed in any of the niches describe above. They occur in open deserts, on the edges of suburbia, within agricultural habitats, and a portion of their kind winter here but then breed in southern Canada. The overall lesson here is that by having flight, birds have been able to slice and dice the available resource niches spatially and temporally in ways unavailable to non-volant species.

This adaptability is remarkable; however, reflecting on Roger Tory Peterson’s quote, does that adaptability make them better or less effective for serving as ecological litmus tests?

In a paper published in 2018, Kelly Iknayan and Steve Bessinger reported findings of their comparisons of historical bird occupancy data in the Mojave Desert, collected by a team led by Joseph Grinnell in the early 1900s, to data they collected a century later at the same sites visited by Grinnell. What they found was an average of a 43% decline in the species occurring at those sites over the past century, a decline they attributed to increased heat and aridity from modern climate change. The only bird to increase over that century was the common raven, an extremely adaptable and intelligent species that has benefited from the waste left by our species. Reading the field notes of naturalists visiting our deserts in the late 1800s through the early 1900s, raven sightings were relatively rare; perhaps one pair was seen over a week of surveying this region’s biodiversity. Today they are seen daily in pairs or groups ranging into double and triple digits. Unfortunately, the ravens’ success has come with a cost to other native species, including desert tortoises (some ravens have learned to specialize on eating baby tortoises). Getting back to Roger Tory Peterson’s quote, yes, birds can be ecological litmus tests, but the directions in which they respond to environmental changes are not always easily predicted.

Birds, along with flying insects and bats, (and pterodactyls of long ago) are a wonder of the power of evolution. Imagine the technology and fuel needed to fly a helicopter or jet airplane, and then reflect on the fact that these species do so much more with so much less fuel, and they fit all the technology and coordination needed to hover, stoop, brake, avoid predators, and migrate thousands of miles in bodies measured in grams and in brains that in some cases are much less than the size of a pea. They can also live and thrive in one of the hottest and driest regions on our planet.

Nullius in verba

Go outside, tip your hat to a chuckwalla (and a cactus), think like a mountain, and be safe