White-browed woodswallow (Artamus superciliosus) - rejection of vulnerable species listing

The Scientific Committee, established by the Threatened Species Conservation Act, has made a Final Determination to REJECT a proposal to list the White-browed Woodswallow Artamus superciliosus (Gould, 1837) as a vulnerable species in Part 1 of Schedule 2 of the Act. Rejection of Vulnerable species is provided for by Part 2 of the Act.

NSW Scientific Committee - final determination

The Scientific Committee has found that:

1. After the exhibition of the Preliminary Determination in May 2009 to support a proposal to list the White-browed Woodswallow as a Vulnerable species; information received from public submissions and associated reinterpretation of available information have led to the conclusion that there are insufficient data to support such a listing.

2. The White-browed Woodswallow Artamus superciliosus (Gould, 1837) is a small (17 cm) songbird, blue-grey on the upperparts and chestnut on the underparts, with a black face and white eyebrows. Its wings are long, pointed and appear triangular when in soaring flight, while the white-tipped tail is often twisted and fanned. The bill is blue-grey with a black tip. The similar Masked Woodswallow  A. personatus is pale grey on the underparts and has a smaller black mask with a white lower rim. Other species of woodswallows are either overall much darker and lack head markings (Dusky  A. cyanopterus, Little  A. minor), paler and plainer (Black-faced  A. cinereus), or have a white rump and underparts (White-breasted  A. leucorynchus).

3. The White-browed Woodswallow occurs in eastern, northern and central Australia. In New South Wales it typically breeds in open forests and woodlands from the inland slopes to the far western plains but during dry years its distribution extends east to open habitats of the tablelands and coast (Higgins et al. 2006).

4. The White-browed Woodswallow inhabits mostly eucalypt, sheoak and Acacia woodland, including mallee, and adjacent open areas including grassland with scattered trees or shrubs. In agricultural landscapes it prefers healthy woodland patches with low disturbance and little grazing (Higgins  et al. 2006). It eats arthropods, including insects that swarm above vegetation, as well as some nectar and small native fruits. Prey is captured aerially and by sally-strike to the ground. The White-browed Woodswallow builds a cup-shaped nest of twigs and plant fibres in a fork, crevice or foliage in a tree or shrub (live or dead), vine, creeper, stump or artificial structure.

5. White-browed Woodswallows are gregarious and form large aerial flocks sometimes consisting of several hundred individuals often in mixed flocks with Masked Woodswallows (Joseph 2009). They also nest in loose colonies sometimes exceeding 50 pairs, with more than one pair occasionally nesting in the same tree (Higgins et al. 2006, Joseph 2009, R Kavanagh, pers. comm. August 2009). White-browed Woodswallows are strongly migratory, with a general southward trend to breed during spring and summer, and a more northerly distribution during autumn and winter (Barrett  et al. 2003). They also exhibit nomadism becoming locally abundant in a region in one year, but being virtually absent the next. For example, White-browed Woodswallows were commonly observed in flocks of several hundred in the Macquarie Marshes in the spring of 2008, but were uncommon there in the spring of 2009 when they were highly abundant near Burke, some 200 km distant (T Hosking, pers. comm. September, 2009). Their patterns of movement have been described as exhibiting a “boom or bust” trend, occurring in vast numbers in eastern Australia in some years, but being virtually absent in others (Joseph 2009).

6. Research on the effects of anthropogenic landscape change has not made a conclusive determination of the response of White-browed Woodswallows to loss of native vegetation. The White-browed Woodswallow’s index of abundance (reporting rate) was found to be positively associated with patch area, the number of remnants more than 10 ha within 5 km, species diversity of shrubs (Seddon et al. 2003) and the amount of native vegetation cover (Barrett  et al. 2007). However, in contrast, Reid (1994) found that the White-browed Woodswallow was one of only four “declining woodland birds” that did not show strong positive correlations with measures of native vegetation cover.

7. The White-browed Woodswallow’s population size in New South Wales is uncertain and assessment is made difficult by the mobility of the species and its gregarious behaviour. There are recent observations of the species being locally abundant (R Kavanagh, pers. comm. August 2009; T Hosking, pers. comm. September 2009), but there is also evidence of a reduction in population size based on comparative atlas results. The species was reported in 81 one-degree grids in New South Wales in the first national bird atlas in 1977-81 at mostly moderate to high reporting rates (Blakers et al. 1984). In the second national bird atlas of 1998-2002 it was recorded in 68 one-degree grids at low to moderate reporting rates (Barrett  et al. 2003). A significant difference in reporting rates was identified from between-atlas comparisons both nationally (38% decline) and in NSW (61% decline) (Barrett  et al 2003, 2007). Declines of more than 20% were recorded in all New South Wales bioregions except the Murray-Darling Depression and Broken Hill Complex, where increases of more than 20% were reported (Barrett  et al. 2003, 2007). However, different survey methods were used in the two bird atlas surveys and some bird species have been demonstrated to vary in their detectability using the two survey methods. The detectability of White-browed Woodswallow was not assessed in the between-atlas comparisons, but the congeneric Dusky Woodswallow was found to have equal detectability between the two atlas periods (Barrett  et al. 2003). While the Dusky Woodswallow is the closest available relative for inferring survey bias, further information indicates that this species is not an appropriate indicator for the White-browed Woodswallows because of differences in the behaviour of the two species. Dusky Woodswallows are not strongly migratory, and they are more evenly dispersed through woodland than the gregarious White-browed Woodswallow. It is possible that the larger grid size used in the first bird atlas was more likely to detect White-browed Woodswallows, making the Dusky Woodswallow a poor surrogate for determining survey bias. Moreover, the boom or bust cycles of White-browed Woodswallows cause considerable uncertainty in inferring a population trend from what are effectively two atlas data points. There are therefore insufficient data available at present to conclude that there has been a moderate decline in population size over an appropriate time period. The degree of threat to the species is also uncertain.

8. The White-browed Woodswallow Artamus superciliosus (Gould, 1837) is not eligible to be listed as a Vulnerable species as, in the opinion of the Scientific Committee, there is too much uncertainty in the available data to demonstrate a moderate decline in population size within a time frame appropriate to the life cycle and habitat characteristics of the taxon.

Dr Richard Major
Chairperson
Scientific Committee

Proposed Gazettal date: 09/07/10
Exhibition period: 09/07/10 - 03/09/10

References:

Barrett GW, Silcocks AF, Barry S, Cunningham R, Poulter R (2003) 'The new atlas of Australian birds.' (RAOU: Melbourne)

Barrett GW, Silcocks AF, Cunningham R, Oliver DL, Weston MA, Baker J (2007) Comparison of atlas data to determine the conservation status of bird species in New South Wales, with an emphasis on woodland-dependent species. Australian Zoologist 34, 37-77.

Blakers M, Davies SJJF, Reilly PN (1984) 'The atlas of Australian birds.' (Melbourne University Press: Melbourne)

Higgins PJ, Peter JM, Cowling SJ (Eds) (2006) 'Handbook of Australian, New Zealand and Antarctic birds (vol. 7)' (Oxford University Press: Melbourne)

Joseph L (2009) Woodswallows: a longer term, evolutionary view of boom and bust. In 'Boom and bust: bird stories for a dry country.' (Eds L Robin, R Heinsohn and L Joseph) pp. 205-222. (CSIRO: Collingwood)

Reid JRW (1994) 'Threatened and declining birds in the New South Wales sheep-wheat belt: II. Landscape relationships - modelling bird atlas data against vegetation cover.' Consultancy report to NSW National Parks and Wildlife Sevice. CSIRO Sustainable Ecosystems, Canberra.

Seddon JA, Briggs SV, Doyle SJ (2003) Relationships between bird species and characteristics of woodland remnants in central New South Wales. Pacific Conservation Biology 9, 95-119.