VOL. 13 (8) DECEMBER 1990 253

AUSTRALIAN WATCHER !990. 13. 253-256 A Nesting Association between the Weebill Smicrornis brevirostris and the Badumna candida by J.N. HOBBS, 12 Hume Street, Dareton, N.S.W. T717

Summary A nesting association between the Weebill Smicrornis brevirostris and the communal nesting spider Badumna candida is described and discussed. Up to 71% of Weebill nests were found in association. Concealment of the Weebill nests is possibly the main purpose. The Yellow-rumped Thornhill chrysorrhoa and Zebra Finch Poephila guttata may also nest in association with the spider. Instances of the association On 19 November 1989 at Dareton, New South Wales, I saw a Weebill Smicrornis brevirostris to a nest of the communal spider Badumna candida situated four metres from the ground in a Black Box largiflorens. In the past I have seen Weebills close to such nests and had assumed they were collecting cobwebs as nesting material ; however on this occasion the Weebill was seen to be carrying material to the nest. Closer observation showed there was a near-complete Weebill nest a few centimetres from the main body of the spider nest, cobweb from which extended to and around the Weebill nest. On 23 November a bird was flushed from the nest, suggesting that incubation had commenced, but three days later the side of the nest was torn out by an unknown predator; the spider nest was untouched. In the same area on 22 November I found another Weebill nest built against a nest of five metres up in a Black Box. The nest was below that of the spiders, its top in contact with the lower part of the spider nest. The relevant area, 4 km west of Dareton, was T7 ha of Black Box woodland which I was surveying regularly for nesting . The two nests described above were the last of a number of Weebill nests found during spring/early summer, but knowing there was an annual resurgence ofWeebill breeding in late summer in this district, I made a special effort in March 1990 to find the nests of the 10 pairs and groups of Weeb ill s known to be occupying the area. To avoid bias I found all nests by following the birds and not by a direct search for nests. Six nests were found built against spider nests. One of these was dismantled by the birds before any eggs were laid, and carried by them to build another nest 78 m away which was also against a spider nest. Four nests were built in typical Weebill sites but not in association with spider nests. Thus of eleven nests of the later summer breeding, seven (64%) were in association with spider nests. All spider nests were examined after the Weebills finished breeding and all were found to be nests of the spider Baduma candida and all contained live, active spiders. As a result of these discoveries I searched two different areas in April 1990 to ascertain if the phenomenon was more general and not confined to one locality. Two groups of Weebills occupy an area of mixed mallee Eucalyptus spp. and Belah Casuarina cristata 1 km east of Dareton. Both had nested in mallee, one nest being built under and against a spider nest. In an area of Black Box woodland 2 km east of Merbein, Victoria, I located four groups of Weebills, two of which were feeding young out of nests which I failed to find . The other two groups were feeding young in nests built against spider nests. In total, from November 1989 when I first became aware of the association to April 1990, I have found 17 nests of the Weebill of which 12 (71%) were built in association with the nests of the spider Badumna candida. AUSTRALIAN 254 HOBBS BIRD WATCHER

RAOU nest records I have examined 180 Weebill nest cards of the RAOU Nest Record Scheme to 1983. One of these (8/67) submitted by S. Marchant, detailing a nest at Canberra, notes the nest site as being 'in twigs of small sapling gum under a large spider's web'. Nest record sheets from 1984 have been examined for me by 1. Starks and he found no references to the association on them. This might suggest the occurrence to be rare or perhaps restricted to my particular district but as I have been consistently active in the field for the past 36 years in many areas frequented by the Weebill and have overlooked the association, it is possible that others may have too. There is no mention of the association with the spider in the Australian literature, but there is a published photograph (Estbergs 1982) of a Weebill nest built in the remains of a nest-sac of Processionary Caterpillars (Notodontidae).

Other instances of association At the site 4 km from Dareton I found two roost nests of the Zebra Finch Poephila guttata built into spider nests. One was thickly lined with feathers and appeared to have earlier been a breeding nest. At the Merbein site I found two nests of the Zebra Finch built on or close to spiders nests. One was found when I saw a Grey Shrike­ thrush Collurincla harmonica apparently extracting something from a spider nest and on examination found the finch nest built on top of the spider nest, an active nest containing many individual spiders. The finch nest contained a broken egg leaking fresh yolk and no doubt the thrush had been consuming this. The second finch nest was built in a clump of Box Mistletoe Amyema miquelii between and touching three active spider nests. It contained four well-feathered young. At the Merbein site I found three nests of the Yellow-rumped Thornhill Acanthiza chrysorrhoa built against spider nests but they were quite old and their history is not known. The spider nests were active ·and one had extended completely round the thornbill nest, with some spiders occupying the latter.

The spider Badumna candida is a communal spider. It builds a nest in the extreme outer branches of a tree or shrub, binding leaves together with cobweb. Webbed tubes extend to the perimeter of the nest and a varying amount of cobweb forming a meshed net is attached to branches surrounding the central nest. The nests vary in size, most being about 100 to 200 nun across, but some are much larger a• .d extend over several branches. The nests may contain up to about 100 spiders, mostly young, the adults leaving to start new nests. Nests may be solitary or as many as ten or more may be found in one tree. In the three localities referred to,'I found that about one tree in thirty contained nests. I have seen them more densely distributed but many large areas of woodland contain no nests at all. The adult female spider is about 7 nun long, the male a little smaller. I have never seen spiders active on the outside of the nest and assume they are nocturnal. No matter how vigorously or delicately the nest was shaken or handled they remained inside the nest. If a nest was pulled apart they ran rapidly. R. Corbould, who originally identified the spider for me, was bitten on his hand and suffered a reddening of the skin and slight discomfort for two days. Badumna candida and its close relatives occur throughout . M.R. Gray of the Australian Museum, Sydney, confirmed the identification of the spider, and the reader is referred to his paper (Gray 1983) for fuller details of and life history. VOL. 13 (8) DECEMBER 1990 Weebill and Spider Nesting Association 255

Weebill nest attached to spider nest, Dareton, N.S.W., April 1990 Plate 66 Photo: J.N. Hobbs AUSTRALIAN 256 HOBBS BIRD WATCHBR

Discussion That birds sometimes nest in association with the nests of stinging or biting social Hymenoptera, e.g. bees, wasps and ants, is well established in Australia and worldwide, e.g. Hindwood (1955), Smith (1985). Association with spider nests has come to attention far less frequently. It has been recorded only for Sunbirds Nectariniidae in Africa (Moreau 1942) and in Sri Lanka (Collias & Collias 1984) and, in Africa, for the Little Grey Flycatcher Alseonax epulatus (Moreau 1942). It is well known that both the Zebra Finch and the Yellow-rumped Thornhill will nest in or against the nests of other birds such as raptors and babblers (Pizzey 1980), and the nesting of these two species in association with the spiders is perhaps a comparable example of this behaviour. An explanation for the Weebill/spider association is not so obvious. In all my observations it was the Weebills that sought out and nested with the spiders, not the reverse, so it is probable that the birds gain some advantage from the association. They could gain: (1) protection from predation by birds, mammals or reptiles; (2) protection from parasitical ; (3) concealment. (1) The example of the Grey Shrike-thrush removing an egg from the nest of a Zebra Finch indicates that an avian predator may not be deterred by the spiders or their webs. (2) One Weebill nest that had been associated with a spider nest was submitted to the Division of Entomology, CSIRO, to assist in the Wool Moth Research Project. M. Horak has informed me that Wool Moths Monopis argillacea were reared from that nest. This may indicate that flying insects may also be undeterred by the spiders or their webs. (3) In 36 years of quite extensive searching for bird nests, I have often noted the conspicuous spider nests and have always moved on without further examination. Perhaps potential predators, birds, mammals and reptiles, could more often than not be equally dismissive. Estbergs' record of the Weebill nest against a caterpillar nest, which closely resembles a spider nest, may add support to the possibility that the association arose through the advantage gained from camouflage and concealment.

Acknowledgements I thank Mike Gray, Johnny Estbergs, Jonathan Starks and Marianne Horak for their assistance and ready response to my queries, and Rex Buckingham for reading my first draft and making helpful suggestions.

References Collias, N.E. & Collias, E.C. (1984), Nest Building and Bird Behaviour, Princeton University Press, Princeton. ' Estbergs, J. (1982), in Serventy, V. (Ed), Ihe Wrens and Warblers of Australia, Angus & Robertson, Sydney. Gray, M.R. (1983), 'The taxonomy of the semi-communal spiders commonly referred to the species Ixeuticus candidus with notes on the genera Phryganoperus, lxeuticus and Badumna (Araneae, Amaurobioidea)', Proc. Linn. Soc. N.S.W 106(3), 247-261. Hindwood, K.A. (1955) , 'Bird/wasp nesting associations', Emu 55, 263-274. Moreau, R.E. (1942), 'The nesting of African birds in association with other living things', Ibis 84, 240-263. Pizzey, G. (1980), A Field Guide to the , Collins, Sydney. Smith, N.G. (1985), Article 'Nesting associations', in Campbell, B. & Lack, E. (Eds), A Dictionary of Birds, Poyser, Calton. Received 25 June 1990 •