Knowledge Gaps 2
On this page we canvass some interesting hypotheses about Australian Sarus Cranes still awaiting investigation. And even the common and better-studied Brolga has its mysteries: for example the New Guinea population is virtually unknown, and the first detailed study of Brolga breeding habitat is only now about to be published.
Issues that are reasonably well-settled – but often not widely appreciated – are in Knowledge Gaps 1. More unknowns on numbers, movements, distribution and breeding are in Ozcranes Brolga and Sarus Crane FAQs.
Nesting & Development
No Australian Sarus nest has been followed from egg to flying young and there are no marked birds. Information like incubation time, first flight and first breeding comes from India or captive birds. Features of first year young still with their parents are being documented but later stages of maturity when the young progressively develop full colours on head, neck, and legs are much harder to establish, without known-age birds. This complicates (at least) population monitoring of older immatures, determining age of first pair-formation and field observation of possible hybrids.
Hybrids
← Brolga-Sarus interactions in the wild, including possible hybridisation, are still unclear (image HANZAB2)
When Sarus Cranes were identified in Australia in 1966 speculation began about interbreeding with Brolgas. The only proven hybrid so far (‘Sarolga’) was bred in captivity (Ozcranes hopes to have a photograph soon, courtesy of the International Crane Foundation). Reports of apparent wild hybrids are based on –
- Unusual head colouring/extent of colouring
- Unusual leg colouring
- Unusual combinations of head and leg colouring
- The above sometimes combined with unusual plumage
- At least one report of a Sarus Crane/Brolga pair with a fledged dependent immature
Apparently there are no photographs from the wild of mixed pairs or possible hybrids. Some scientific literature has stated (on the above basis) that wild Brolgas and Sarus Cranes hybridise, but molecular studies have so far found no supporting evidence. More blood or feather samples for testing are a priority. Some birds may hybridise, or, as with initial assumptions that the Brolga and Sarus Crane were sister species, features observed in the field can be misleading. They may be primitive (shared due to a common ancestor), derived (evolved) or convergent (similar in form and function, but not related).
TOPHabitats
← In the Dry Season, some Sarus Crane pairs roost at scattered waterholes along sandy watercourses on Cape York Peninsula (cranesnorth, CYP). The largest known wintering population concentrates on the inner (wetter) Atherton Tableland, while Brolgas occupy drier hinterlands
→ Typical Sarus Crane nest site habitat in the Gulf of Carpentaria, NW Qld. Brolgas nesting in the same area choose more open sites (John Grant)
As outlined in Sarus Crane FAQ3, Sarus have been observed using fewer habitats than Brolgas but records from areas with both species give no broad indicator of habitat choice based on ‘wetter’ vs. ‘drier’ environments. Without more detailed information on characteristics of habitats used by either or both species, it seems premature to be predicting conflict or exclusion between them, or whether land use changes will advantage one species over the other, and so on.
One key Sarus habitat issue has been better documented. Australian Sarus seem very selective in choosing nest sites compared with Brolgas, and compared with Indian Sarus Cranes that breed successfully in open sites like flooded paddy rice fields. All the data so far sugggest they particularly choose swampy melaleuca woodlands and smaller wetlands on treed ridges. Further work is needed to –
- identify major nesting areas other than the Smithburne-Gilbert Fan Aggregation NW of Normanton & vicinity
- identify finer-grained habitat characteristics of nest site selection
- using Landsat imaging and GIS, estimate available potential nest habitat of this type
Archibald, GW & Swengel, SR. 1985. Comparative ecology and behaviour of Eastern Sarus Cranes and Brolgas in Australia Proceedings of the 1985 Crane Workshop, pp. 107-116.
Beruldsen, GR. 1997. Is the Sarus Crane under threat in Australia? Sunbird 27, pp. 72-78.
Borad, CK; Mukherjee, A & Parasharya, BM. 2001. Nest selection by the Indian Sarus Crane in the paddy crop agroecosystem. Biological Conservation 98, pp. 89-96.
Sarus conservation
← Sarus Crane flock (David Stowe)
Sarus Cranes overseas are increasingly under pressure despite major efforts in some countries. Australia is a signatory to international agreements on migratory waterbirds that include the Sarus Crane. As a result, potential impacts on Australian Sarus are considered in Environmental Impact Statements for developments like windfarms on known or assumed migration routes. But the State of Queensland where most Australia Sarus and all known breeding sites are found, classifies Sarus at the basic protection level of ‘Common Wildlife’. Thus there is no provision to allocate environmental funding or enable sustainable use agreements for Aboriginal hunting, and so on (note the comment from one advisor on the Fencing Whiteboard that potential wetland fencing impacts on Sarus Cranes are ‘not a sustainability issue’). The Action Plan for Australian Birds 2000 lists Sarus at the base level of ‘Least Concern’.
Comments on how cranes fare in Queensland and Northern Territory NRM Plans are on Ozcranes NRM page. Any major change (eg weeds, fire regime, drainage) that particularly impacts on the Sarus Crane's apparently restricted nesting habitats in the breeding areas could have a serious impact on already low Sarus recruitment rates. Given as well uncertainties about population size and the stability of roost sites essential to the wintering Tablelands population, a review of conservation status for the Australian Sarus Crane seems overdue.
More..
The 1992 baseline for Brolga and Sarus knowedge gaps, many still unexplored, is in HANZAB2. Ozcranes FAQ pages cover more unknowns on Brolgas and Sarus.
