Articles by John Grant

Thank you to Dr John Grant for permission to post Research Reports (slightly edited for web) on aspects of his crane studies. This article was first published in 2012 and covers breeding season surveys in the Gulf of Carpentaria. The articles are copyright accounts of studies in progress and should not be cited without permission of the author. For ecological and foraging studies for Sarus Cranes on the Atherton Tablelands, and an account of the first attempt to satellite track an Australian Sarus Crane, see Articles Part 1».

‘Gulf Crane Surveys’ was published in the BirdLife Northern Queensland newsletter, 2012. BirdLife Northern Queensland provided some funding for continuing post-breeding surveys in the Gulf.


Gulf Crane Surveys

Introduction

Sarus and young in Gulf

Surveys of Sarus Cranes Grus antigone on breeding areas in the south-east Gulf of Carpentaria were undertaken over four days in mid March 2012, with the aims of estimating density of breeding birds and documenting habitat use during the breeding season.

← Sarus and young in the Gulf (David Stowe)

As this population of Sarus Cranes is poorly known and has only been examined in any detail on the breeding grounds on one occasion (Archibald and Swengel 1985), further studies are required. The density of nesting pairs recorded in the 1985 study at Delta Downs (Morr Morr) Station was very high, with approximately 1.1 pairs per square kilometre, rivalling the highest known densities of breeding cranes anywhere on earth, such as those recorded by Sundar and Choudhury (2008) for Sarus Cranes in Uttar Pradesh, India. The breeding areas in Australia are shared by Brolgas G. rubicunda, also recorded in high density by Archibald and Swengel (1985), so that total crane breeding density in the southeastern Gulf is likely to be the highest known, making this a globally important site. More recently the area has been recognised as such by its listing as an IBA by Birdlife International.

Archibald and Swengel (1985) also documented differences in breeding site selection between Brolgas and Sarus at Delta Downs, suggesting that competition between the two species may be lessened by the apparent habitat partitioning. They also suggested, however, that if Sarus numbers were increasing, as was thought at the time, increased competition for breeding habitat could occur and Sarus, which appeared to them the behaviourally dominant species, could displace Brolgas and come to predominate further (in 1985, Sarus outnumbered Brolgas by a ratio of 3 to 2 at Delta Downs). Some further aims of this survey were then to document comparative habitat use by the two species in some unstudied sites, record interspecies interactions, and to examine the current proportions of the two species.

top TOP

Methods

Juvenile Sarus

Early morning point counts in different habitats were used to estimate relative densities of cranes, with unison calling pairs of both species recorded as to distance and direction from the observer's position.

← John Grant surveys Gulf cranes, early morning (K.S. Gopi Sundar). Companions are Swati Kittur and Inka Veltheim

Vehicle transects were conducted on the Normanton to Burketown road (the ‘Gulf Track’), and to a lesser extent (due to road closures) on the Burke Developmental Road, with habitat scanned for cranes along slowly driven sections of road between fixed observation points, where larger areas could be scanned from an elevated position (the roof of the vehicle).

Cranes continued to unison call periodically for much of the morning and occasionally thereafter, so morning counts from the fixed survey points (spaced 0.5 to 2km apart) included records of calling birds not visible in more densely vegetated areas. In these cases distance estimations were again used to approximately plot calling birds; experience over this period and on previous surveys gave an effective detection distance for unison calling birds of up to 2km; calling birds that were visible at various estimated or measured distances gave support to this as a maximum detection distance in calm conditions (which prevailed during these surveys).

Cranes encountered were identified, aged (see Grant, 2005) and grouped according to apparent breeding categories:

For each observation, birds were plotted from the fixed positions or from opportunistic sightings while driving, using GPS co-ordinates of observer position with compass direction and estimated distance of birds. Each sighting or aural record was accompanied by habitat observations, broad while in the field (e.g. floodplain, Eucalyptus woodland, etc.) and refined later by reference to regional ecosystem maps available from DEHP. Habitat condition was also recorded, in particular extent of flooding.

top TOP

Results and Discussion

Using an effective detection distance of 2km, the area surveyed on the Gulf Track transect was estimated at 20 sq km, and yielded totals of 20 potential breeding pairs for Sarus and 7 for Brolgas. The density of presumed breeding pairs was thus 1 pair of Sarus per sq km and a total of 1.35 crane pairs, combining both species. Five pairs with accompanying immature young also were recorded in the survey area, and some of these, in some years, undoubtedly breed also, based on observations of pairs reaching the Atherton Tablelands with immatures belonging to successive age classes (J. Grant, unpublished observations), so the density of breeding pairs may be higher. The next scheduled survey trip (April) may shed some further light on this. Additional pairs were undoubtedly missed during surveys also, as most records came from the more open habitats, but many of the calling birds were in woodland; pairs in more densely wooded areas of the transect (approximately 30% of this survey area) were presumably often undetected if their calls did not coincide with observer census times.

Total density of cranes recorded in this survey transect was approximately 4 per sq km, in a ratio of 3.4 Sarus to 1 Brolga. It was clear that pairs of each species occurred in the same habitat types, with most of the observed pairs in Regional Ecosystem (RE) 2.3.4 (Blue grass Dichantium spp. And Brown top Eulalia aurea grassland on plains of cracking clays) and RE 2.3.10 (Coolibah Eucalyptus microtheca and box E.chlorophylla low open woodland and Broad-leaved tea tree Melaleuca viridiflora woodland and savannah on plains). These presumed breeding territories (again more observations in April will make this clearer) appear to show a high degree of overlap in habitat use, contrary to some earlier suggestions, perhaps simply reflecting different behaviour in different locations, but may also indicate more competition than previously thought for breeding habitat. No observations were made of direct interactions between the species, though one observation of a ‘standoff’ by calling birds, one pair of each species, suggested neighbouring territories may be defended interspecifically.

Early morning surveys on the accessible part of the Burke Developmental Road, in densely wooded habitats (mainly RE 2.3.10) gave estimated densities of Sarus at 0.8 pairs per sq.km, slightly below that of the Gulf Track survey area, and no Brolgas. Possibly the open plains are a more favourable habitat for both Sarus and Brolga.

Further fieldwork will help clarify some of the observations made in the March surveys. Reliable estimates of density will help in identifying some of the habitat types surveyed as Critical Habitat for one or both of the crane species; at present none of the habitats in the survey areas, mapped in the RE maps from DEHP, are indicated as critical habitat for any species in the accompanying documents. Further evidence of habitat use by nesting birds of both species will be of use in deducing their inter-relationships and helping to work out the dynamics of the long-term interaction between the species.

References

Archibald, G. W., and S. Swengel. ‘Comparative ecology and behavior of Eastern Sarus Cranes and Brolgas in Australia.’ In Proceedings of the 1985 Crane Workshop, pp. 107-116. 1987. (Download from Ozcranes Downloads»)

Grant, John DA. ‘Recruitment rate of Sarus Cranes (Grus antigone) in northern Queensland.’ Emu 105, no. 4 (2006): 311-315.

Sundar, KSG and Choudhury, BC Impact of Land Use Changes on the Ecology and Habitat of the Sarus Crane (Grus antigone antigone) in the Indo-Gangetic Flood Plains: Part II. Uttar Pradesh. Wildlife Institute of India, 2008.

top TOP

«Back to John Grant Articles Part 1


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. He is a member of the the Crane Specialist Group.


Change AT to @ and DOT to . in email addresses