Although our Sky Island region is renowned for a plethora of wildlife – from bees to butterflies and mammals to monsters (Gila, that is) – perhaps we are most famous for our bird diversity. Enter April. Spring migration is now well under way, heralding the return of a veritable slew of neotropical migrants. These are species who have evolved to vacate our rather hospitable winter climes in deference to the opulence of more tropical habitats.
Why do they head south and why do they return if the tropics are such a good deal? The obvious answer to the riddle of why some of “our” bird species head south for the winter is food. Most of our neotropical migrants feast primarily upon invertebrates, which decrease significantly during an Arizona winter. At the same time the tropics offer a veritable smorgasbord. Further, this pattern of migration may well have its foundations in the Ice Ages, when heading south was even more imperative. Back then the local winters were much harsher with even fewer food provisions. Even when Arizona winters became more mild and invertebrate food more readily available, the ancestral pattern of spending energy via migration to get more energy in the tropics persisted in some species.
Why, then, return to Arizona and other points north from the tropics? The answer may well be competition. The tropics are already famously crammed with breeding bird species that have evolved to exploit local habitats to raise their young. Further, the seasonal glut of resources – from swarms of breeding termites and ants to legions of flies and other insects – in more temperate Arizona and beyond can even temporarily surpass the year-round food abundance in the tropics. Think monsoon season. Hence, the strategic advantage of losing energy via migration to maintain and restore winter fat reserves in the tropics and then to produce healthy offspring in the Sky Islands. A potent combo.
Obviously not all our local birds are neotropical migrants. Some are resident species, which make no large seasonal movements. Greater roadrunners, cactus wrens, and bridled titmice fall into this category. They grace us year-round, though some resident species make rather minor movements as weather dictates, particularly up and down in elevation. Then there are wintering species, who, as their title implies, mainly inhabit the Sky Islands during colder months. White-crowned sparrows, sage thrashers, and Lawrence’s goldfinches are among this crowd. April is a prime time for birding, as resident, wintering, and neotropical migrants are all present.
Who are some of April’s wayfaring birds? Even some of our hawk species tilt south for the winter, searching for more abundant food. Swainson’s hawks often make an epic journey from Arizona all the way to Argentina and nearby locales. Most of our more tropical-leaning hawk species – zone-tailed, common black, and gray – vacate the Sky Islands, but the shift is a more minor one to Mexico and Central America. Sticking with raptors, two of our diminutive owls, elf and flammulated, complete a similar seasonal shift to the nearby tropics.
Still, when most people think of the return of birds in spring, it’s not raptors that they have in mind. Instead, they muse upon passerines – the so-called songbirds of the world. Now the list of returning species swells tremendously. Some returning birds are just passing through our region, while others will stay here to raise a brood or two of young. New World flycatchers comprise the largest bird family on Earth and seriously embellish our April birds. Watch for olive-sided flycatchers, greater peewees, dusky-capped flycatchers, sulphur-bellied flycatchers, and various kingbird species staging their return.
Though we host some wintering vireos, Bell’s and warbling are generally not among them. At our Raven’s Nest Nature Sanctuary, I listen with attentive ears for the scribble-like song of the former as a sure sign that spring has indeed sprung!
Some swallow species also mount a comeback, sweeping the skies like so many miniature baleen whales while feeding upon insects instead of fish or krill. Look too for an explosion of warbler species, which color our local habitats. Some of the more flamboyant include Grace’s warbler, red-faced warbler, and the aptly named yellow warbler. Beware of warbler neck while craning your head upwards in an effort to find and identify such arboreal species.
Not to be outdone in the colorful returnee category are some members of the cardinal family. Some stunners include the tanagers – western, hepatic, and summer – as well as black-headed and blue grosbeaks. Watch for a trio of gaudy orioles, blackbirds in disguise. Hooded, Scott’s, and Bullock’s orioles once again stalk our local haunts in April. Finally, leaving songbirds behind for a second, enjoy the return of some hummingbird species, including blue-throated and Rivoli’s.
If you are already a birdwatcher, then enjoy the visual and auditory feast that is April. If – shame on you – you’ve yet to grab a pair of binoculars, then I entreat you outside this month. Whether alone or with a seasoned guide, April is sure to inject excitement and life into even the most housebound soul!
Vincent Pinto and his wife, Claudia, run RAVENS-WAY WILD JOURNEYS LLC, their Nature Adventure & Conservation organization devoted to protecting and promoting the unique biodiversity of the Sky Islands region. RWWJ offers a wide variety of private, custom-made courses, birding & biodiversity tours. Visit: www.ravensnatureschool.org