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Articles by John Grant
Thank you to author Dr John Grant for permission to post Research Reports (slightly edited for web) on early stages of his crane studies. This first page covers recruitment and foraging studies for Sarus Cranes on the Atherton Tablelands, hybrid cranes, and the first attempt to satellite track an Australian Sarus Crane. For crane breeding studies in the Gulf, see Articles Part 2».
Tablelands studies
Demographic and ecological studies of Sarus Cranes on the Tablelands
‘Demographic and ecological studies of Sarus Cranes on the Tablelands’, John Grant, originally published in Crane News 2002, edited E. Scambler. A paper on recruitment rate was published in 2005.
Over the past eight years I have started building up a picture of the age structure and foraging habitats of the Sarus Crane population that winters on the Atherton Tablelands. At present we know almost nothing of the population dynamics of Sarus Cranes in Australia, with even the total population size a mystery (published estimates range from 5,000 to 10,000 birds).
However, with several thousand birds wintering on the Tablelands, there is the opportunity to obtain some basic demographic data on a good-sized sample of the Australian population. Examining the age structure of the Tablelands birds can help us to understand such parameters as recruitment rate, overwinter mortality, year-to-year fluctuations in survival rates and, in the long term, the overall trend of the population. With long-lived birds such as cranes, it is important to build a solid foundation of these data so as to enable future comparisons.
Age structure
Some interesting findings from my preliminary analysis are:
← Juvenile Sarus (David Stowe)
- the recruitment rate (measured as the percentage of juvenile birds in the population) is currently quite stable from year to year at around 6%
- juvenile overwintering mortality (measured as change in percentage of juvenile birds from early winter through to October) is close to zero
- the proportion of juveniles goes through the roof in November, indicating that older birds are departing early (presumably to their breeding grounds), and younger birds follow later, or as we have seen in some summers, remain on the Tablelands in small numbers
Much more remains to be discovered, and with several more age classes appearing identifiable in the field (with experience, a telescope and considerable eye strain), the potential exists for much more sophisticated demographic analysis.
Foraging sites
Foraging habitats of the Sarus Cranes (and Brolgas) on the Tablelands have so far been surveyed mainly in the Atherton-Malanda-Yungaburra-Kairi area. In most years, cranes of both species have been concentrated on corn stubbles, with a good amount of time also spent foraging in more well-grazed cattle pastures
This year, however, and possibly as a result of a very poor corn crop, cranes are using pastures more often and are also feeding in a wider variety of other situations, even including cane trash where they have been very rarely seen in the past. As this unusually dry year progresses, we may see more changes in crane behaviour and distribution.
MORE: Dr KS Gopi Sundar reports on John Grant's recruitment studies in Breeding for Success, a story of the Sarus in Queensland»
TOPSarus-Brolga hybrids
An old acquaintance not forgot
Originally published in Wingspan, March 2014 page 36.
When I first mentioned hybrid cranes in a Wingspan article in 2004, there was some scepticism. The fact that Sarus Cranes and Brolgas segregate by habitat on the breeding grounds was presented as one of the main arguments against introgression. While nesting pairs of the two do indeed select different parts of the Gulf to breed in, this is essentially irrelevant to hybridisation since courtship and pair formation occur outside the breeding season. The two species come into close contact on the Atherton Tablelands, and dancing Brolgas are often joined by Sarus, especially immature birds, clearly stimulated by the movements which are so similar to those of their own species.
I have been watching cranes closely for 17 years, and although I may be simply getting better at spotting intermediate birds, my impression is that hybrids – first noted by George Archibald in 1981 – have become more common over that period. This is perhaps not surprising, as the two species have been wintering together on the Tablelands for a relatively short time as their presence can only date as far back as the clearing of the area's forests about 100 years ago.
The majority of hybrid birds appear to pair with Brolgas. A number of these pairs have been seen with progeny, indicating that the hybrids are fertile. Several different ‘morphs’ occur, perhaps representing different generations and back-crosses, many of them larger than both parent species.
The genetic relationship of Brolgas and Sarus Cranes presents an interesting history. The two are each other's closest relatives, their shared ancestry diverging when Brolgas became the first wave of cranes to colonise Australia, breaking away from their Asian relatives about three million years ago.
Australian Sarus, by contrast, seem to have split from their South-East Asian conspecifics as recently as 30,000 years ago, arriving here to find the Brolga adapted to the dry continent, including its development of a salt gland and the ability to live in deserts.
The long isolation of the two species has obviously not rendered them reproductively incompatible. Upcoming genetic work by Tim Nevard will help to clarify the dynamics of the hybridisation process. Tim has asked that if anyone has sightings of potential hybrids to report them to him [see Tim Nevard's page in Ozcranes Research»].
Bird in the Hand..
..the first Australian Sarus Crane (almost) to be satellite tracked
‘Bird in the Hand’ was written for Ozcranes and BirdLife Northern Queensland website, 2008. BirdLife Northern Queensland provided some funding for the 2006 attempt to satellite track an Australian Sarus Crane for the first time. Gulf flood image courtesy courtesy NGRMG.
In mid-May 2006 the Gulf country was still largely inaccessible. Flooding in the wake of cyclone Monica the previous month had left the seasonal wetlands high and wide, making our chances of locating young Sarus Cranes that much more remote. With satellite transmitters and permits in hand, and accompanied by Rigel Jensen and Merryl Baetge, I had come out to Karumba with high hopes of obtaining the first data on movements of these cranes, maybe even tracking their annual migration to the Atherton Tablelands.
A reconnaissance the previous February had shown that many pairs of adult cranes were on territories in the flooded woodlands, but nesting had seemingly not yet commenced. So by now I expected to see many juveniles, including some as yet unfledged and therefore catchable. Our methodology was simple and in the established tradition of crane-catching – see a young crane, run it to ground!
As usual, the theory proved deceptively straightforward, firstly because we found only one flightless juvenile (I speculated that many eggs or chicks had been lost in the floods) and second its skill at eluding capture was far greater than our hunting prowess. This half-grown chick was adept at disappearing into the neck-high grass as its parents led us away in opposite directions. After several unsuccessful attempts over two days, we spotted the family in an open area and Rigel and I sprang from the braking car. Our speed caught the birds by surprise, and the chick dropped while still in short grass - even so, it lay so well camouflaged that I almost trod on it before it hissed and broke cover. It soon gave up the chase as two of us closed in, and barely struggled as we put a hood over its head. It weighed in at a healthy 4kg (adults range from 5 to 8kg), more than enough to carry the 30g transmitter without ill effects. This was mounted on a specially designed legband, a system used successfully in north America, where monitored birds showed no adverse effects on behaviour or reproduction. As the adult birds flew wide circles above us, calling loudly, we fitted the transmitter and recorded vital statistics in about 15 minutes. On release, the youngster spread its wings and ‘craned’ to its full height, posturing defiantly until I backed off. We watched it walk away, apparently unencumbered by its new load, before leaving so that the family could reunite.
Having tested the transmitter satisfactorily beforehand, we waited expectantly for the first fixes, relayed by David Roshier from Charles Sturt University, who had donated the transmitters. Anticipation turned to profound disappointment as a day, then two, passed with no signals received. The realization that the transmitter had been damaged soon after deployment (most likely by some vigorous pecking at the antenna) was truly deflating, but on the brighter side there may still be a young crane wearing a very expensive legband, fetchingly bright red and inscribed with the code ‘K01’ in large print. So there is still a chance we may learn something from our bird. He or she has not been sighted on the Tablelands yet. In 2006 many fewer cranes than usual arrived, presumably remaining on the Gulf plains which were unusually green well into the year. Despite larger numbers in 2007, there were still no sightings. This year may be different, so if you happen to spot ‘Karumba’, on the Tablelands or in the Gulf, or anywhere else for that matter, please let me know!
Next: John Grant Articles Part 2»
About the authorJohn» is a professional zoologist working in teaching and research, with a particular interest in Sarus Cranes. He has been studying the recruitment rate and feeding substrates in the wintering population of Sarus on the Atherton Tablelands since 1997. Both studies have reached the significant stage of 20 years of survey data, and writing is in progress. John's other work includes Sarus breeding ecology in the seasonal Gulf of Carpentaria wetlands and the maturation stages for Australian Sarus. John is a member of the the Crane Specialist Group and other articles on his long term work with Sarus Cranes can be read on Ozcranes.
