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Are Black-faced Woodswallows indicators for other birds in Australia’s northern savannas?

Justine Rice | 2023 Graham Harrington Student Research Scholarship recipient


Editor’s Introduction

Justine Rice, the author of this Research Project update, was the recipient of the 2023 Graham Harrington Student Research Scholarship (for which she achieved First Class Honours). This annual Scholarship was established by BirdLife Northern Queensland (BLNQ) in recognition of noted ornithologist, Dr Graham Harrington, to encourage student researchers to pursue the systematic study of threatened northern Queensland birds; share their discoveries; and contribute to the understanding and conservation of our birds.

Justine undertook an Honours Research Project to determine if focusing search efforts on Black-faced Woodswallows (Artamus cinereus) would increase our ability to detect the Endangered Black-throated Finch (Poephila cincta cincta), which has disappeared from over 80% of its former range. Black-throated Finch has a strong association, in mixed-species flocks, with Black-faced Woodswallow, which is more conspicuous due to its aerial hawking of arthropod prey.


Australia’s northern savannas are facing perplexing avifaunal declines, and there is a need to identify the primary drivers if further declines are to be prevented. Northern savanna birds are unevenly dispersed across vast, privately owned rangelands, contributing to low species detection rates and hindering research efforts.


The bird behavioural phenomenon known as ‘mixed-species flocks’ adds to the uneven dispersal of savanna birds. Mixed-species flocks include ‘leader species’, which are often conspicuous, even from a moving vehicle, and ‘follower species’ which are often less conspicuous. Searching for conspicuous leader species could provide a solution to the low detection rates of less-conspicuous species by signifying areas with mixed-species flock activity.

A mixed-species flock of Black-faced Woodswallow, Double-barred Finch, and Black-throated Finch. Image by Justine Rice.


Black-faced Woodswallows (Artamus cinereus) have been reported to lead mixed-species flocks, and act as sentinels for less-conspicuous follower species such as Black-throated Finch (Poephila cincta). The southern subspecies of Black-throated Finch (Peophila cincta cincta) is nationally Endangered, and its rarity has contributed to our lack of understanding regarding the species’ ecology and conservation needs.

Black-faced Woodswallow. Image by Justine Rice.
Four of the nationally Endangered Black-throated Finch southern subspecies. Note the identifying white rump of the upper bird. Image by Justine Rice.


An individual Black-throated Finch: southern subspecies. Image by Justine Rice.

My study investigated the association between Black-faced Woodswallows, Black-throated Finch, and the broader bird assemblage, to establish if Black-faced Woodswallows are useful indicators for the presence of mixed-species flocks and, if so, whether Black-faced Woodswallow detection-based surveys are a useful tool for improving the detection rates of other birds in the northern savannas.


I spent five weeks conducting surveys within the Desert Uplands bioregion of central Queensland, where three of the four extant populations of Black-throated Finch persist. To investigate the association between Black-faced Woodswallows and the broader bird assemblage, particularly Black-throated Finch, I conducted bird and habitat surveys at ‘treatment’ sites where Black-faced Woodswallows were detected, and at paired ‘control’ sites where they were not present.

The northern savanna comprises vast rangelands across which northern savanna birds are unevenly dispersed. Image by Justine Rice.


The results of my study revealed that Black-faced Woodswallows were useful indicators for birds that tend to associate with them in mixed-species flocks, as both bird species richness and abundance increased markedly in their presence with no other habitat variable ecologically explaining their presence.


The association between Black-faced Woodswallows and the other bird species is likely to be a direct behavioural association, in which the other bird species are responding to the Black-faced Woodswallows acting as sentinels, and forming mixed-species flocks.


Twenty-six bird species (out of a total of 60: that is, 43%) were recorded in the presence of Black-faced Woodswallows at treatment sites, but never in control sites where Black-faced Woodswallows were absent. Conversely, only seven (12%) of bird species were found only where Black-faced Woodswallows were absent.


Therefore, surveying areas where Black-faced Woodswallows were present may be a useful way of increasing the efficiency of surveying for other species that associate with them in mixed-species flocks.


Black-faced Woodswallow detection as a bird survey method may also present an effective way to monitor population trends of other birds that tend to associate with them in mixed-species flocks. Monitoring participation rates in mixed-species flocks, for species that associate with Black-faced Woodswallows in mixed-species flocks, may provide an opportunity for early identification of those species’ declines. The implementation of Black-faced Woodswallow-detection as a species monitoring method might have been deployed too late to be used as an indicator of Black-throated Finch decline in my study region.


In summary, my research concluded that Black-faced Woodswallows were useful indicators for the presence of other birds that associate with them in mixed-species flocks in my study. Therefore, the use of bird surveys that take advantage of the conspicuous nature of Black-faced Woodswallows, and their association with less-conspicuous species, may assist in improving detection rates in future studies, particularly for species with low detection rates, such as the Black-throated Finch.


It is also likely that Black-faced Woodswallows could be useful indicators for species declines and provide a more effective method for monitoring avian population trends. Mixed-species flocks are not unique to Australia’s northern savanna and as such, using indicator species of mixed-species flocks as a bird survey method could prove a promising approach to improve the detection of inconspicuous birds in other ecosystems.


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