Do Male Roadrunners Feed to Females
It seems everyone has a lot of questions about roadrunners (Geococcyx californianus) lately, including how to determine sex. Many observant people have noted that some roadrunners have a colorful post-orbital apterium (the patch behind the eye) while others do not. It was once thought possible to determine sex depending on the presence of white or blue in this area(PDF warning), but current research indicates this method to be unreliable. The only reliable field method to visually sex a living roadrunner is to take measurements of the bill length and width as well as measurements of the foot. Besides the ethical concerns of chasing down a bird just to satisfy your curiosity, as you might imagine, they are difficult to catch! While it is unfortunate Roadrunners do not display as visible sexual dimorphism as many other birds (think of the white coloration of a male bobwhite and the tan coloration of a female bobwhite), it is still fantastic to observe the little differences between individuals.
Another popular recent myth
Another often asked question is whether roadrunners impact northern bobwhite populations through predation. The reasoning is that roadrunners are very successful predators of small animals including rodents, lizards, snakes, and even other birds. Since quail chicks start life the size of a marble and spend the first few weeks of their lives smaller than a golf ball, it is easy to imagine roadrunners quickly taking a brood of bobwhites. It doesn't help that northern bobwhite are a species that have suffered a huge population decline in the last century, and biologists, landowners, hunters, and nature lovers are desperately exploring the driving forces behind that decline. This has led to some too quickly pointing fingers, and roadrunners have been a victim in the past. The truth is that there is no evidence to support the claim that roadrunners are negatively driving bobwhite populations. A Texas Parks and Wildlife Department project (PDF warning) examined the stomach contents of 118 roadrunners and found two bobwhite chicks out of many prey items. In a landscape plagued with drought, unmanaged grazing, and abundant mammalian nest predators, there is a long list of more likely culprits.
So, what do they eat then?
The shorter list would be what roadrunners will not eat. From insects to rodents, lizards, snakes, birds, and plants, they are adapted to survive in the sometimes food scarce American Southwest. In 1998, I observed a roadrunner kill several cliff swallows by laying as flat as possible near a building and suddenly making an explosive jump to snatch a diving swallow from the air. After each kill, the roadrunner would carry the dead swallow to the base of a fence post and then return to hunt again. Later, the roadrunner carried off all of the swallows to a location I could not observe.
In addition to hunting for food for themselves, food plays a large role in roadrunner courtship. Males attempting to woo a mate will bring her bride-gifts. If she accepts the gifts, the new couple with build a nest together, with the male bringing the female nest material. While both sexes will incubate and tend the nest, the male will often bring the female food while she sits on the nest. This is another reason why causal observers make over estimate the influence of Roadrunners on prey species populations: while it may appear a single roadrunner is a blood thirsty killing machine, it may in fact be feeding half a dozen other roadrunners.
I may eventually write a full species account for the roadrunner for this blog, but a fantastic resource to learn more is Dr. Martha Maxon's wonderful natural history book, The Real Roadrunner (paid link). It is very approachable by general interest readers while maintaining scientifically accurate information.
(Cover photo: Dawson County, 2017).
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Updated 2022.
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Source: https://instantemense.com/2016/09/09/sexing-roadrunners/
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