By Chris MacColl.
Red Goshawks are inherently rare owing to their relatively small population size (currently estimated at 1,340 individuals) spread over a wide distribution spanning the sub-tropical and tropical belts of eastern and northern Australia, at least historically. This endemic bird of prey has long been a mystery to western science: for more than 200 years, our collective knowledge comprised a few anecdotal reports, one breeding account (Lord, 1952), and a total of 46 skins held by museums both in Australia (22) and overseas (24).
Jack and Lindsay Cupper gave us the first intimate account of life inside the nest whilst photographing adults and young from atop a 35m tower on the Wenlock River in 1980. Soon after, the Royal Australian Ornithologists Union (RAOU – now Birdlife Australia) funded the first detailed study of the species in the Top End and Kimberley between 1987 – 1990. Drs. Tom Aumann and David Baker-Gabb led that seminal piece of work providing us with our current level of understanding on their breeding biology and ecology. Tom and David also undertook some of the earliest radio-tracking studies in Australia by attaching tracking devices to the tails of a male and female throughout part of the 1987 breeding season in Kakadu National Park. This was the first information collected on the species’ movements, particularly as it relates to their foraging behaviour whilst breeding. Such insights were hard won as the researchers had to pursue birds on-foot or by vehicle with a radio receiver to try and determine how far they would venture from the nest and in what direction. Thirty years later, the information we can now collect thanks to a quantum leap in animal tracking technology is truly remarkable.
The transmitters used today are micro-sized and allow us to answer all types of questions about a species’ spatial ecology, such as their home range, habitat selections, and movement patterns. Satellite telemetry allows us to determine the position of individual Red Goshawks no matter where they go on the earth’s surface. This ability to communicate with satellites enables the tracking data to be transmitted remotely straight from the bird’s back to the researcher’s home computer. This means we never have to re-capture or re-locate the tagged birds in order to acquire the tracking information being collected as can be the case with other types of tracking units. The data we receive is mostly GPS data meaning that the geo-locations being captured are accurate to within 18m. But what makes the information truly powerful are the timescales over which we are monitoring each individual for: a tracking device attached to a Red Goshawk today may contribute 2 to 3 years’ worth of data before the battery finally expires (and the tag eventually falls off thanks to a weak link).
We are now able to see seasonal and annual behaviours, and how they might change with varying environmental conditions such as wet and dry years. We are able to tell if a juvenile bird survives its first, second, or even third years, by which time it probably becomes a breeding adult itself with a nest and territory. We can also see if an adult is a year-round resident on its breeding territory and what the environmental make-up of that territory is, or if it chooses to migrate elsewhere during the non-breeding season and where that might be.
In terms of a research schedule, our Red Goshawk tracking studies are still in a data collection phase, with a number of birds still being actively tracked and new ones being added to our pool. Still, the information we have been able to collect thus far is significantly shaping our understanding of this species. Prior to this work, it was believed that northern Australian birds would be year-round residents (Aumann and Baker-Gabb, 1991), and whilst this has proven correct for some individuals, others migrate large distances each year between defined breeding and non-breeding season home ranges, some in unexpected environments. Adult females #157650 and #66559 are both migrants moving between seasonal home ranges as shown in the animation below. #157650 moves more than 1000km each year from her breeding territory in northern Cape York Peninsula down to the Einasleigh Uplands region. #66559 has a seasonal home range in the upper Victoria River district on the edge of the Tanami Desert, which she sometimes forays into. Upon returning to breed this year #66559 decided to leave her partner of the past two seasons (at least) and take up with a new male from a neighbouring territory! Fortunately the deserted male soon found himself a new female and now thanks to tracking this one bird we have new information on inter-pair distances and breeding behaviour.
Tracking juveniles departing their natal territories and trying to survive on their own is another key part of this research. We’ve been fortunate to track a number of them over multiple years now and have important information on their dispersive behaviours and survival rates. Juvenile females #66560 and #66561 were both tagged in December 2019 after they had reached a semi-independent state and soon departed their parents’ territories to go it alone. Both females successfully navigated their first 12 months of independence with #66560 even attempting to breed in her first year; totally unexpected in a species of this size (see stationary movement in the tracking animation). Breeding success increases with age as individuals become more experienced, and we are happy to report that #66560 appears to be breeding again this year with the tracking data suggesting it is going well so far. The nesting location is 8.5km from last year’s indicating that it is likely to be with a different male, thus providing us with the location of two new breeding territories!
This kind of information and the technology that enables its collection is greatly enhancing our understanding of this rare and threatened species. We are using it to guide recovery actions through the national Red Goshawk recovery team of which we are members. This research wouldn’t be possible without the vital support received by each of the partner organisations contributing to this project’s implementation – Rio Tinto Weipa, the Australian Wildlife Conservancy, the Queensland Department of Environment and Sciences, and the University of Queensland via the RARES Group.