Typical Polygyny and Cooperative Polygyny in Ridgway's Hawk (Buteo ridgwayi)

Abstract

Avian mating systems are often monogamous, although polygamy in the form of both polyandry and polygyny are regularly employed by some species and opportunistically practiced by others. Among raptors, multiple species within the genus Buteo have been documented using either polyandrous or polygynous strategies. Here, we describe the first known cases of polygyny in Ridgway's Hawk (B. ridgwayi), a small forest hawk endemic to the island of Hispaniola. This raptor has been studied since the mid-1970s, and intensively during the last 20 yr. Ridgway's Hawks are generally considered to be monogamous; however, we report here observations of polygynous behavior in a recently established, wild population. We consider these polygynous breeding events opportunistic responses that display behavioral flexibility that may serve to benefit the conservation of this critically endangered raptor.

Pre-breeding behavior of Ridgway’s Hawks (Buteo ridgwayi) in Punta Cana, Dominican Republic

“…Although none of the focal individuals were seen in close proximity to other pairs aside from one documented territorial flight, we did observe one juvenile female interacting with an adult pair on 19 January. Notably, this juvenile hawk eventually joined that pair as a polygynous trio in 2018, and again in the three subsequent breeding seasons (Hayes et al 2022). The male of this pair was later documented copulating with both females, and both females incubated eggs, fed nestlings, and defended the nest territory (Hayes et al 2022).…”

“…Notably, this juvenile hawk eventually joined that pair as a polygynous trio in 2018, and again in the three subsequent breeding seasons (Hayes et al 2022). The male of this pair was later documented copulating with both females, and both females incubated eggs, fed nestlings, and defended the nest territory (Hayes et al 2022). Our single observation of the juvenile bird and one of the adult hawks lowering their legs in flight in close proximity to each other appeared consistent with aggressive flight displays documented by Wiley and Wiley (1981), but we observed no other evidence of aggression during these early encounters between the juvenile female and the pair.…”

“…Further study should assess rates of extra-pair paternity in Ridgway's Hawk broods in Punta Cana, especially in broods raised by polygynous trios like those documented in Hayes et al (2022). If rates of extra-pair paternity are higher in Punta Cana than in Los Haitises, where hawks appeared to be strictly monogamous, this could help explain frequent copulations between members of a social pair.…”

“…), but this is uncommon for the species overall (Anderson et al 2021). To date, polygyny has only been documented in the Punta Cana population, never in the Los Haitises population, and polygynous events account for about 8% of occupied nests in Punta Cana between 2011-2021 (Hayes et al 2022).…”

“…Given that these copulations were observed more than a month before the typical egg-laying date, it also seems unlikely that these copulations would have produced any fertilized eggs. Perhaps with a higher-density population of hawks, an overall younger population in Punta Cana than in Los Haitises, and a higher frequency of polygamous events (Hayes et al 2022), male hawks in Punta Cana have greater need for forms of mate guarding such as frequent copulations.…”