The Sarolga: Brolga-Sarus hybrids

Ozcranes looks at the earliest sightings of ‘Sarolgas’ in northern Queensland in 1972, followed by years of field observations – and speculation. Recent genetic research has confirmed hybridisation in the wild. This is more common than indicated by sightings of apparent hybrids, and the future implications for both species (and Sarolgas) in the north are uncertain.

The first Brolga-Sarus hybrids known to ornithology were not found in the wild in Australia, but were bred in captivity in France in the 1930s: for the history of these Sarolgas see Sarolgas in France». See also Ozcranes Brolga breeding» and Sarus breeding».


Australia, 1972: Discovery

Sarolga hybrid

In 1972 George Archibald of the International Crane Foundation photographed the first known Sarolga in Australia on the Atherton Tablelands, and collected a specimen. This was a hybrid between the Australian Sarus Crane Antigone a. gillae and the Brolga A. rubicunda. Archibald also observed an apparent F2 hybrid, a backcross between a Sarolga and a Sarus Crane [1].

← Brolga-Sarus Crane hybrid, 2013, Atherton Tablelands (courtesy John D A Grant»)

Archibald continued discussion of the implications of hybrids in a second paper on Sarus and Brolga breeding in the Gulf Plains [2], and both articles are available from Ozcranes Downloads». From the mid 1990s, John Grant, Tim Nevard and others began to search for apparent hybrids in wintering crane flocks on the Atherton Tablelands. in 2004, John wrote an article ‘Secrets of the Sarus Crane’ in Wingspan (former magazine of BirdLife Australia) including observations of hybrids:

I pause to take a better look at an unusually marked bird – it is grey-legged like a Brolga, with the bright yellow eye of that species (the Sarus Crane has a darker, reddish eye), but the red of the head is more extensive than on a typical Brolga, and the dark dewlap on the throat is barely present. Several birds show features intermediate between the two species, and this particular bird is one of the most convincing arguments I have yet seen that hybridisation cccurs in the wild.

Brolga and Sarus

← Immature Sarus Crane and adult Brolga acting as a pair, Hasties Swamp, Atherton Tablelands 2007. Courtesy Jan O'Sullivan.

This generated quite a lot of sceptical comment, as John noted ten years later in BirdLife Australia's new magazine:

When I first mentioned hybrid cranes...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...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.

He added that after 17 years watching the cranes, hybrids seemed to be more common. They usually paired with Brolgas, and there were many variations of hybrid features. (Both John's articles can be read in full on Ozcranes, see links in Sidebar).

Notes: In the first photo above, this Brolga-type hybrid on the Atherton Tablelands was taller than the accompanying Sarus Cranes, and had a range of intermediate features, including a larger than usual comb, a slight bulge in the throat rather than a dewlap, grey legs with a tinge of pink on the ‘thighs’, and the short cap and overall pale body colour of a Brolga without that species' obvious scalloping on the upperparts. The Brolga and immature Sarus above are displaying typical behaviours of a pair in response to disturbance, by engaging in synchronised distraction preening. In the Sidebar (above right), the (presumed) male Sarus Crane takes an upright alert posture while the (presumed) female Brolga takes a submissive posture.

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Genetic studies

Introgression is the transfer of genetic information from one species to another as a result of hybridisation between them and repeated backcrossing. Following years of field observations as outlined above, Tim Nevard and colleagues [3] proved the existence and extent of wild hybridisation between Australian Sarus Cranes and Brolgas through genetic analysis of samples from blood, tissue and moulted feathers. Samples were from the Atherton Tablelands and Gulf Plains, plus some reference samples from pure-bred captive birds.

Simplified graphic of genetic introgression due to hybridisation of Brolgas and Sarus Cranes (after Nevard et al. 2019 [3]).

Hybrids

Birds in the black rectangle are hybrids (‘Sarolgas’). Brolgas on the left (blue), look like Brolgas but a (small) number have a component of Sarus genes (red). Sarus on the right (red) look like Sarus but a (smaller) number have a component of Brolga genes. The incidence of hybrids revealed by genetic analysis is 10 x the number than can be distingished from obvious features in the field. All details can be found in Nevard et al. 2019 [3].

Future directions?

The future evolutionary and conservation directions from this ongoing hybridisation in northern Australia, are unknown. The Sarolga could possibly evolve over time, into a new, separate species. Also unknown, is how long hybridisation has been occurring, and whether the rate of genetic change is increasing as (perhaps) more and more hybrid Sarolgas interbreed with purer bred Brolgas and Sarus Cranes. Tim Nevard and team are continuing work on these aspects, collecting more shed feathers for future analysis. For more on this project, see Tim Nevard research».

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References

[1] G. Archibald. 1981. Introducing the Sarolga. pp 213-215 in: Lewis JC, Masatomi H, eds. Crane research around the world (Symposium). See Ozcranes Downloads»
[2] G. Archibald, S Swengel. 1987. Comparative ecology and behavior of eastern Sarus Cranes and Brolgas in Australia. Proceedings of the 1985 Crane Workshop, ed JC Lewis: 107-116. See Ozcranes Downloads»
[3] T Nevard, M Haase, G Archibald, I Leiper, & ST Garnett (2019). The Sarolga: conservation implications of genetic and visual evidence for hybridization between the Brolga Antigone rubicunda and the Australian Sarus Crane Antigone antigone gillae. Oryx 54: 40-51.

Next: Brolga-Sarus hybrids in France, 1930s»

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