Raptors, or birds of prey, and owls, are important indicators of environmental health.
Dr Stephen Debus
School of Environmental and Rural Science.
Raptors, or birds of prey, and owls, are important indicators of environmental health because they are at the top of the food chain. Their population trends can signal ecosystem stability (or dysfunction), and their propensity to accumulate, and be affected by, toxins such as pesticides and heavy metals (notably lead) can signal potential health risks for humans exposed to such chemicals. New England-North West provides an ideal case study for environmental health because it is typical of an intensively farmed and grazed landscape, with increasingly cleared and fragmented woodlands. It is also home to many threatened flora and fauna species, where water is increasingly scarce under global warming.
Over the last few years, Steve Debus, together with UNE students and interested amateur observers, has researched four avian species found in this area, including the White-bellied Sea-Eagle, Little Eagle (small cousin of the Wedge-tailed Eagle), Black Falcon and Barking Owl. These declining species are scheduled as threatened fauna (category Vulnerable) in NSW. The focus of his work has been on determining their ecological requirements, such as diet and nest-site characteristics, in conjunction with a survey, commissioned by Local Land Services, of their nests across different land tenures.
The White-bellied Sea-Eagle is a large grey and white eagle, similar in size to the Wedge-tail that breeds on inland waterbodies. At several reservoirs, Steve has many times seen an eagle swoop to snatch a fish from the water surface, and eagles pursuing ducks in full flight. Observations include many altercations between Sea-Eagles and either Wedge-tails or ravens over the Sea-Eagles’ nest sites, with the Sea-Eagles sometimes swooping at their opponents.
With honours student Candice Larkin, Steve has located 15 Little Eagle nests. Together, they saw the defending eagles make lightning swoops at an intruding raven near their nests. Eagles courting or advertising their territory perform vigorous undulating display dives high in the air. Steve has also seen Little Eagles make fast or stealthy dives to the ground to catch a rabbit, or fast dives to the tree or shrub canopy to try to catch a bird, and was told that a local observer saw a Little Eagle catch a lorikeet in flight.
Meanwhile, some of Steve’s colleagues in Canberra found, by satellite telemetry, that a Little Eagle migrated for the winter to the Top End of the Northern Territory before returning to his breeding territory in spring – a journey of over 3,000 km each way, and soaring to a height of 8,000 metres above sea level while travelling.
With honours student Alice Bauer, Steve has studied four pairs of Black Falcons at Tamworth. This is of particular interest to researchers as these falcons only occasionally visit the Tablelands. They have spotted them catching birds in fast pursuit or dives. Steve says this is typical of a bird-hunting falcon; giving the example of the Black Falcon’s equivalent in Africa being measured by GPS telemetry in dives of up to 141 km/hr.
Local surveys, undertaken by Steve and Candice, have located several nests of the Barking Owl on the Tablelands, but the researchers still need more information. Steve says that research is always helped by local amateur observers and he welcomes people letting him know what they have seen, and where they have seen it.
Sightings of raptors and their foraging are by no means limited to the wilds—Steve says they can be seen in town. Collared Sparrowhawks and Australian Hobbies hunt and apparently breed in or near the Armidale suburbs, and Steve is keen to find out where. Black Falcons hunt feral pigeons over the CBD of inland cities and Steve says he has seen a Peregrine Falcon swoop over his house in Armidale, diving at and chasing a Galah. These birds have been GPS-tracked in dives at up to 196 km/hr. Candice Larkin, who is starting a PhD with Steve in 2019, will be looking at raptor nesting in the Tablelands.
To help with identification of these difficult birds, Steve has produced two small books: Bird of Prey of Australia: A Field Guide, due as a third edition in 2019, and with Richard Seaton and Mat Gildfedder, Australian Birds of Prey in Flight: A Photographic Guide, just published (both by CSIRO Publishing).