Deforestation threatens one of the worlds largest eagles

2 July 2021

One of the world’s largest and most endangered eagle species face further risk from rainforest destruction, new research from the University of East Anglia (UEA) finds. 

Harpy eagles (Harpia harpyja), which are arguably the world’s largest eagle species, struggle to feed offspring in heavily deforested areas of the Amazon, according to a new study from researchers at UEA and the University of KwaZulu-Natal in South Africa. 

The research, ‘Tropical deforestation induces thresholds of reproductive viability and habitat suitability in Earth’s largest eagles’, is published today in Scientific Reports

Dr Everton Miranda and colleagues found that harpy eagles rely on specific mammal prey that live in the forest canopy, including sloths and monkeys – but these mammals are also dwindling in numbers because of habitat loss. 

The authors observed prey species, how frequently prey was delivered, and estimated the weight of prey arriving at 16 harpy eagle nests in Amazonian forests in Mato Grosso, Brazil, using cameras and meticulously identifying prey bone fragments. They also referenced maps and high-resolution satellite imagery to calculate deforestation levels and estimate forest disturbance around each nest. 

The authors identified 306 prey items, nearly half (49.7 per cent) of which were two-toed sloths, brown capuchin monkeys and grey woolly monkeys. The authors’ observations indicated that harpy eagles in deforested areas did not switch to alternative non-forest prey, and delivered canopy-based prey less frequently and with lower estimated body mass. 

Eaglets starve to death in areas of high deforestation where canopy-based prey items are limited, and the study calculates the maximum deforestation threshold that precludes reproductive viability in rearing young.

In landscapes with 50-70 per cent deforestation, eaglets died from starvation, and no active nests were found in areas that had been deforested by over 70 per cent.

The authors calculated that areas with over 50 per cent deforestation are unsuitable for harpy eagles to successfully raise offspring and estimate that around 35 per cent of northern Mato Grosso is already unsuitable for breeding harpy eagles. This may have caused a decline in numbers of breeding pairs by 3,256 since 1985.

The authors conclude that as breeding harpy eagles rely on specific food and rarely hunt in deforested areas, harpy eagle survival critically depends on forest conservation.

Prof Carlos Peres, a Professor of Conservation Biology at UEA and an author in the study, said: “The geographic range of many forest species in the Amazon, including harpy eagles, is rapidly declining, but this is aggravated in apex predator populations sustained by large areas of suitable habitat.” 

Dr Miranda, who recently concluded his PhD in South Africa, said: “Considering that harpy eagles have the slowest life cycle of all birds, their chances of adapting to fragmented forest landscapes are nearly zero. Retaining forest connectivity, translocating juveniles and food supplementation to eaglets then become critical if they are to persist in these human-modified landscapes.”