High in the rafters of a suburban Cincinnati library, a pair of red-shouldered hawks is raising their brood—and that brood likely skews female. After thirty years of meticulous fieldwork tracking these medium-sized raptors across forests, suburbs, and urban spaces in Ohio, researcher Cheryl Dykstra has uncovered something remarkable: hawk parents strategically produce more female offspring when living in better territories with abundant prey.
The finding, published in the Journal of Raptor Research, reveals a nuanced biological strategy that illuminates how wild animals respond to their environment—and offers biologists a new lens for understanding habitat quality. It also underscores how hawks are thriving as urban neighbors, adapting to a landscape increasingly shaped by human development.
The mechanism is elegant. Dykstra's team discovered that red-shouldered hawks possess the ability to adjust the sex ratios of their offspring before hatching, essentially choosing to invest more heavily in female chicks when conditions permit. Why females? Females are roughly 25% heavier than males and require significantly more energy to rear—a costly proposition when food is scarce. But in resource-rich territories, the payoff justifies the investment. Biologists theorize that females offer parents a genetic advantage: they can begin breeding earlier than males, meaning their offspring will contribute genes to the population sooner, accelerating the family's reproductive success.
The data supporting this pattern comes from a comprehensive dataset spanning 2004 to 2016, gathered by Dykstra's team working across rural, suburban, and urban environments. By the time hawk nestlings reach three weeks old, their leg and foot measurements reveal their sex—allowing researchers to correlate territory quality with the proportion of males to females in each nest. Higher-quality territories, containing more prey, consistently produced more female nestlings. The pattern had been observed in other raptors, such as Eleonora's falcons and lesser kestrels, but this three-decade study from Ohio provides particularly robust confirmation.
The team also uncovered secondary patterns worth noting. Solitary nestlings are more likely to be female than male. Eggs laid later in the breeding season, meanwhile, are more likely to hatch male, regardless of whether the territory is rich or poor—suggesting that as resources dwindle seasonally, parents shift strategy.
What makes this research especially relevant is its focus on urban-adapting hawks. Red-shouldered hawks once thrived primarily in forests, but increasingly they nest on library rooftops and in suburban settings. This shift brings new ecological questions. Urban hawks face threats that their forest-dwelling cousins do not: vehicle collisions, exposure to rodenticide from the rats they hunt, and different patterns of human activity. Understanding these differences is critical for developing protection plans that actually work across the species' expanding range.
Dykstra emphasizes the human dimension of raptor conservation. "The relationship between humans and urban-adapting birds is critical for conservation," she notes, adding with warmth that "few people can resist the appeal of an awkward, half-feathered nestling raptor." Her team continues to involve the public through nestling-banding activities that build local awareness and appreciation for these top predators, which play vital ecological roles that often go unnoticed. As hawks claim a place in cities and suburbs, fostering that appreciation may prove as important as the science itself.