Are you outside? Look up, look around you, and if you don't spot one immediately, wait a few minutes. Your chances of seeing a common raven (Corvus corax) are very good. These jet-black birds with glossy, iridescent feathers, chisel-shaped black bills, and wingspans of up to four feet are ubiquitous in the Mojave and Colorado deserts. But this wasn't always the case. Ravens were uncommon in the California deserts in the first half of the 20th century; wildlife biologists now estimate that raven populations have increased here by approximately 1000 percent in the last 35 years. How has this happened? Although the question cannot be answered with any finality, much of the raven's success seems to hinge on its innate intelligence and its ability to exploit conditions provided by human habitation. Wherever people are, ravens thrive. They are world-class opportunists.
It has been said that more has been written about the raven than about any other bird. Even before recorded history, Native Americans told many stories about the raven, the majority of which characterized it as a mischievous and clever animal. Perhaps ravens fascinate us because they have been observed playing with sticks and passing stones to each other, and they have been taught to count, mimic human speech, and to read the face of a clock. Ravens reportedly mate for life (although this statement has been contested by some observers) and they have an extraordinarily diverse vocabulary of vocalizations. The social life of a raven is complex. These birds are very gregarious and sometimes form groups composed of as many as one hundred individuals. Their ability to produce a wide range of sounds may attest to a sophisticated avian vocabulary that, although largely impenetrable to humans, allows them to express themselves and communicate a vast amount of information crucial to their survival. A begging nestling, for example, will eventually produce a "yell call," which is thought to bring the attention of other juvenile ravens to a newly-discovered food supply.
Other types of vocalizations include "vocal play," a sort of warm-up repertoire that prepares the young raven for more advanced sounds. After being fed, nestlings will produce "comfort sounds," consisting of a soft quiet medley. If a person disturbed a raven's nest, or a bird of prey flew overhead, the raven might issue a "predatory alarm," a series of short high-pitched keck-keck-keck calls. When in flight, a raven might produce a "demonstrative call" to announce its presence within a particular territory. If it is being pursued by another raven whose territory it has invaded, it will utter "chase calls." "Knocking calls" are made only by females, either to establish their dominant status within a group, or in displays where they are being courted by a male. Surprisingly, ravens in the wild do not appear to mimic other sounds. The ability to mimic human speech has been clearly observed only in ravens raised in isolation. Ravens may live as long as 50 years. They reach sexual maturity at about two to three years old, and after breeding the female typically lays three to seven eggs, out of which two to four young birds may successfully fledge.
It is the female who appears to do most of the nest-building, although males assist in the process by delivering twigs and sticks to the female as she constructs a nest first by stacking the larger pieces and then by weaving a cup from the smaller branches and twigs. Once the eggs are laid it takes about 18-20 days for them to hatch. Over the course of the last two decades ravens have earned a villainous reputation among naturalists in the California deserts - they have been identified as one of the main predators of desert tortoise (Gopherus agassizii) hatchlings, a species listed as "threatened" on the federal Endangered Species List. Early efforts made by several agencies to mitigate the raven's impact on desert tortoises have had limited success. Raven populations continue to increase while tortoise populations remain in decline. Where tortoises usually suffer from loss of habitat due to human encroachment, ravens often prosper: open landfills provide acres of available food; roadways become slaughterhouses for wildlife subsequently consumed by scavengers such as ravens; utility poles provide excellent nesting platforms; and pet food left outdoors where it is accessible to ravens, coyotes, and other scavengers tips the scales of survival - to the detriment of other species.
Whereas a certain number of ravens usually die off each year due to a natural reduction in seasonal food sources, the availability of a steady supply of pet food has reduced that number. Ravens are neither predators nor scavengers - they are both. Some of their energy income is collected through predation while another portion is obtained by scavenging, but when people unwittingly provide them with fast food in the form of dog chow or shredded fishheads, why should they bother to hunt for a gourmet meal? They're shrewd enough to grab what they can, when they can. And grab they do. How is it that the human presence in a landscape can have such radically disparate impacts on different species? The answer may lie in the innate behavior of those species and how they are or are not able to adapt to the human influences imposed on them.
Desert tortoises need open land with enough vegetation to sustain them and space in which to forage for that vegetation. They also need plenty of earth in which to dig their burrows. Ravens do not have those same requirements - they are able to find what they need in a landscape shrunk by human development yet swollen with the detritus often introduced by human civilization. In order to help restore the balance between ravens and tortoises, and between ravens and the other species they affect, we can become aware of some of our current practices and change them.
These are some of the things we might do to help control raven populations:
(1) Keep a lid on all garbage receptacles.
(2) Cover and store food if you leave your campsite during the day.
(3) Do not feed any wildlife!
(4) Observe the speed limit: speeding increases the incidence of roadkill accidents.
(5) Use drip irrigation in your yard: pools of water attract ravens.
(6) Bring pet food and water bowls indoors when they are not being used by your pets.
Although we did not intentionally create the recent explosion in raven populations, it seems as though we have inadvertently enabled ravens to dominate the California desert landscape. If we behave responsibly today, we may yet restore balance to the desert ecosystem. If not, certain species may become a tale of nevermore. by Park Ranger Caryn Davidson