Researchers have recorded an extraordinary case of nest usurpation in South Africa where a crowned eagle successfully incubated the eggs of an Egyptian goose.
An article published in the Journal of Raptor Research details an incident involving a pair of crowned eagles (Stephanoaetus coronatus) on the Zimbali Estate, north-east of Durban. In 2025, they were found to be incubating a single egg of their own alongside two eggs of an Egyptian goose (Alopochen aegyptiaca).
Remarkably, the eagles showed no willingness to reject the goose eggs in what is believed to be the first authenticated example of interspecific clutch mixing involving this species.
Endemic to much of sub-Saharan Africa, the Egyptian goose does not construct a nest but instead uses tree cavities or simply lays a clutch beneath a bush or in dense undergrowth. They also use vacated nests of other birds, or employ a method known as nest usurpation, where they forcibly occupy nests already being used by other species.
Their popularity as an ornamental species has seen feral and introduced birds colonise parts of the Middle East and Western Europe, where they may usurp the nests of medium-sized raptors, such as common buzzards (Buteo buteo) and Eurasian goshawks (Astur gentilis).
The crowned eagle is a large, bulky raptor with a long tail and relatively short wings, perfectly built for forestine habitats where they are found. They are long legged and possess powerful talons with which they prey predominantly upon mammals up to the size of monkeys and antelopes.
In recent years, the species has adapted to suburban habitats, exploiting remnant tracts of forest, such as that found on the Zimbali Estate where the birds are monitored by The Crowned Eagle Research Project and co-authors of the study, Petra Sumasgutner, Brendan Smith, and Shane C. Sumasgutner.
Their research includes remote camera operation and live streaming of nests, and this specific 30-metre-high platform nest has provided prior footage of usurpation behaviour by Egyptian geese.
In 2012, the resident eagles were continually agitated by a pair of geese as they incubated their single egg. Despite the interference, the eagles successfully fledged an eaglet, whereafter the geese laid and brooded six eggs of their own.
In July 2025, a pair of crowned eagles were active at the site, bringing fresh nesting material and mating on the nest. While the eagles were absent, an Egyptian goose laid two eggs in the nest which were subsequently found and incubated by the female eagle alongside an egg of her own.
The geese remained in proximity, occupying the nest if both eagles were absent, but quick to depart on their return. The goose eggs hatched at the end of August, whereupon the eagles offered the hatchlings food which was refused.
Egyptian geese are precocial, with goslings normally leaving the nest within 24 to 48 hours, and the first to hatch made the 30-metre jump from the platform after two days.
However, as the second gosling became more active, the eagle continually tucked it under her body, typical of nestling retrieval in raptors. At one point, the gosling climbed onto the eagle’s back, prompting a dramatic shift in behaviour from the female eagle, who then attacked and predated the gosling.
The recorded events show a remarkable tolerance of crowned eagles to both the eggs and young of another species, but also prompts concern for native species, particularly medium sized raptors, where Egyptian geese are invasive.
Find out more about the study.
Top image credit: Brendan Smith
More wildlife stories from around the world
- Remote cameras capture woodcocks aggressively charging deer in West Virginia
- Oregon’s biggest city was drowning in crow poop. Then a new predator came to town
- “I was photographing seabirds on a remote island off Norway. Then a huge predator appeared from nowhere”
- Great crested grebe seen drowning and eating chiffchaffs in Spain
