It is a truth universally acknowledged that a lone common black hawk in no possession of a child, must be in want of a mate, no matter their genus… So begins the tale of one common black hawk’s foray with a red-shouldered hawk, despite their genetic differences. Yet this story does not end in tragedy, for this intergeneric affair has resulted in the natural production of an extremely rare hybrid, an event recorded only a handful of times in wild hawks and eagles.
The unconventional tale began in 2005, when Stan Moore, a raptor bander at Fairfax Raptor Research, noticed an unusual sight in the Laguna de Santa Rosa Wetlands Complex in Sonoma County, California: a common black hawk (Buteogallus anthracinus). More commonly found in corridors of gallery forests along flowing streams from the Southwestern United States through to South America, the common black hawk has only been spotted 16 times over a period of 33 years in California.
Although a temporary resident for the first two years, the common black hawk Moore had spotted started to hold a permanent territory from April 2008. During this time the hawk, later determined as female after Moore tagged her in 2009, had already begun to engage in mating behaviors, enticing the native red-shouldered hawks (Buteo lineatus) into her territory. But she did not receive a warm reception, having been harassed by a resident pair of red-shouldered hawks during several of her aerial courtship displays.
Their refusal of her advances is not wholly surprising, given that the two species of hawks belong to entirely different genera, only sharing common ancestry at the “family” level. Therefore, the black hawk’s uniform dark plumage would be seen as a world away from the red hawk’s rusty and white speckled front. The female black hawk’s superior size may also have been on the male red hawk’s mind, as the size contrast would have posed a significant threat to them.
So what was it that attracted the female black hawk to the male red hawk in the first place? Well, according to a paper published earlier this year in the Journal of Raptor Research, the answer is probably not love but in fact desperation.
Hubbs’ principle, referred to as the “desperation hypothesis,” is one way in which hybridization can be explained. This is when “a rare individual fails to find a conspecific mate and settles on a mate of a common species,” a rarity caused, for example, by vagrancy, endangerment, or natural range expansion, according to the authors.
Therefore, away from her species, the vagrant black hawk in western California had to change up her type in order to mate, and the red-shouldered hawks were the most abundant species available, although their dietary overlap and strong associations with aquatic habitats may have helped them along.
After several years of mating behavior, a suspected hybrid juvenile was sighted in 2012. Ramping up their observations, the researchers recorded a total of three courtship flights, two copulations, and two simultaneous nest attendances between the female black hawk and a male red hawk, which ultimately resulted in another hybrid birth in 2014.
Marrying the two species’ appearance, the offspring was large and had a dark plumage, similar to its mother, and had a hooked bill and patches of cream and dark brown, like its father. Although the offspring’s appearance and the behavior between the two hawks point to a hybrid, a genetic analysis of the juvenile’s blood sample would confirm it.
But what of the adult hawks’ fate? Reports and photographs from 2019 show the pair engaged in aerial courtship displays. The less cynical amongst us may wonder that what perhaps was once an act of desperation has turned into love after all.