Bumper count of Brolgas in SW Victoria

Part of a larger group of brolgas surveyed west of Casterton

Part of a larger group of brolgas surveyed west of Casterton

In late April this year, observers again spread out across south-west Victoria to count brolgas at their annual flocking sites. The count had two aims: to get a better estimate of total population size, and to estimate the proportion of young birds in flocks to give an idea of the amount of successful nesting that had occurred in the previous two years. Young brolgas can be aged with confidence to about 2 years old.

 

Counters searched previously known flocking sites in the following areas: Willaura, Penshurst, Lake Bolac, Streatham, Darlington, Camperdown, Strathdownie, and Bool Lagoon. Bool Lagoon near Naracoorte in South Australia was included because brolgas are known to move between south-west Victoria and South Australia.

 

A total of 907 birds were counted on the day. The largest flock recorded on the day was a massive 320 birds at Strathdownie counted by Richard and Ros Collins. Numbers for Penshurst were also high, down from a maximum count of 268 earlier in the season to 241 on the count day. A flock of 100 birds were counted at the Willaura flocking site.

 

The first estimate of the Victoria brolga population was 600-650 birds by  Arnol et al. (1984) with approximately 550-600 birds in south west Victoria. The smallest total reported in previous flock counts in south-west Victoria was 402 by Phil Du Guesclin in 2002, and the largest was 675 from 2004 by Rebecca Sheldon. This is only the second year in which counts have been undertaken systematically by having different sites counted on the same day across the state. Previous counts from the late 1980s to 2000s are thus not comparable to the counts from 2012 and 2013. Nevertheless, the large number of young birds in flocks in the past three years and highly unusual sightings of several flocks of sub-adult Brolgas during the breeding season of 2012 both support the conclusion that there has been a substantial increase in total brolga numbers in south-west Victoria in this period.

 

Large numbers of juveniles and sub-adults were found in this year’s counts, with an estimated 17% of all birds counted being either juvenile or sub-adult (less than two years old). This number is at the upper end of values found for south-west Victorian flocks and is similar to last year’s result. Such high proportion of juveniles and sub-adults in flocks also suggests that breeding success has been higher over the past two years than in previous years. In contrast, the count in 2009 recorded a proportion of only 3% birds less than two years old in counted flocks. These age structure counts are helping us gain a better understanding of breeding success in the southwest and in the longer term, the viability of this south-west Victorian population.

 

This year all counts were done on a single day, following the advice of Inka Veltheim, PhD candidate at University of Ballarat, who has found that flocking brolgas can move quickly between flocking sites. A simultaneous count of sites across the region gives greater confidence that the number did not include any individuals counted twice. Although the vast majority of birds are considered to flock to these traditional sites, some brolgas can be resident year round at their breeding wetland if they retain water and food resources. Breeding sites are not counted in annual flock counts, and thus these counts represent an underestimate (presumed small underestimate) of the total population size in south-west Victoria.

 

In conclusion, these counts are allowing us to produce a more accurate picture of the population size and status of our iconic brolga population. Recent results showing substantial increase in successful breeding suggest that breeding success is markedly increased in years of good winter-spring rainfall, and that securing or improving wetland filling for brolga nest sites should be a key focus of brolga conservation in south-west Victoria.

Richard Hill, DEPI, Casterton.

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