142 AUSTRALIAN Field Ornithology 2010, 27, 142–145 Australasian Activity on a Flood-retarding Basin

VIRGIL HUBREGTSE 6 Saniky Street, Notting Hill, Victoria 3168

Summary This paper reports observations of breeding activity of Australasian novaehollandiae, the movement and survival of a nest when the water-level rose rapidly, and an intruding Grebe feeding one of the resident ’ young.

Introduction The Australasian Grebe Tachybaptus novaehollandiae is widely distributed in . It is found on a variety of shallow bodies of fresh water, from small dams to large lakes and marshes, mostly with some fringing vegetation. It is secretive and wary, and usually occurs singly or in monogamous pairs. The nest consists of a soggy platform of waterweeds, usually not far from the shore, and is concealed amongst vegetation. Young birds are fed by the parents until they are old enough to find their own food, and are fully independent at 8 weeks of age. Breeding losses are thought to be high because of fluctuating water-levels, weather and predation (Marchant & Higgins 1990). Between October 2006 and April 2010, Grebes nested eight times on the flood- retarding basin located at the Clayton campus of Monash University in suburban Melbourne, Victoria. Despite occasionally adverse conditions, only one nesting attempt failed. This paper includes a report of the movement and survival of a nest and eggs when there was a rapid rise in water-level, and observations of an intruding Grebe feeding one of the resident birds’ young.

The location The flood-retarding basin at the Clayton campus of Monash University is ~200 m long. At the wider (western) end it is ~80 m across. There is a patch of bulrushes Typha sp. at each end, and an outlet covered by a grille near the eastern end, for excess water to flow through.

Observations The observations were made opportunistically, generally three times per week, during walks around the flood-retarding basin since 2000.

2002 Australasian Grebes were first observed on the basin on 5 May 2002, when two birds were present. Approximately 4 years and 5 months elapsed before this was seen there again. VOL. 27 (3) SEPTEMBER 2010 Australasian Grebe Breeding Behaviour 143

2006–2007 In October 2006, two Grebes were present and nested in the bulrushes at the western end of the basin, raising five young. In February 2007 the Grebes built another nest in the bulrushes, near where the first had been. This nest failed, presumably because of intrusive and noisy construction activity nearby; the Grebes often swam near the eastern end of the basin, but they made no attempt to nest there, possibly because of frequent human activity. Both Grebes stayed on the basin for some time, but both eventually departed. One was present on 11 September 2007, and one was seen from time to time until January 2008.

2008 Late in January, two Grebes built a nest among the waterweeds in the north- western section of the basin. One of the birds was on the nest on 3 February and subsequently. On the morning of 7 February the nest was gone after heavy overnight rain and a rise in water-level. What may have been the remains of the nest were floating several metres from the nest-site. The Grebes were not seen for more than 2 weeks, but on 23 February they were calling from near the bulrushes at the western end of the basin. The following day they were seen at the same place with four tiny chicks. From 6 March to 22 April only one adult and three young birds were seen, but on 23 April all six birds were present. By 7 June only two adults and one young remained, and they left in June or July. By 2 November, a pair of Grebes had nested in the bulrushes at the western end of the basin and raised three young.

2009 During January, a pair of Grebes built a nest out in the open at the western end of the retarding basin and occupied it for ~4 weeks. On 24 February there were young in the nest, and 3 days later the adult Grebes were seen swimming with three young. During the second and third weeks of March usually one but sometimes two ‘new’ adult Grebes, in breeding plumage, were present. The resident Grebes seemed to spend more time trying to chase away the newcomers than feeding their own young. On 28 March three adult Grebes were present, and each was feeding a young one; each group of two Grebes was well separated from the others. On 30 March one young bird was diving frequently, and the adults were rejecting the young. On 6 April the three groups of two were still intact, although one young bird was chased when it snatched a food item from a surfacing adult. The three adults were chasing the young birds, which were now about full size. AUSTRALIAN 144 HUBREGTSE Field Ornithology

From 7 April one of the young Grebes seemed independent, and on 10, 12 and 13 April just one of the three young birds was pestering an adult for food, but without success. On 27 April and subsequently only two adult Grebes, presumably the original pair, were present on the retarding basin. Later in 2009 a pair of Grebes raised four young, two in September and two in December. The latter nest survived inundation, unlike a nearby Eurasian Coots’ Fulica atra nest that failed.

2010 In March the Grebes raised three young. Previously, they had not bred so late at this location.

Discussion

Rising water-level and disappearance of the nest When the water-level in the retarding basin rose, on 7 February 2008, somehow the eggs and at least part of the nest must have been saved, because, with an incubation period of ~23 days (Fjeldså 2004) there was not time for the birds to build, lay and incubate again: the chicks were only a few days old when seen on 24 February. Although it is possible that the motion of the rising water moved the nest, it is unlikely that it would have concealed the nest in the bulrushes. There is no mention by Marchant & Higgins (1990) of Grebes being able to move their nest or eggs, but there is a suggestion that breeding losses are ‘probably high, caused by fluctuating water-levels, weather and predation.’

The intruder feeding the residents’ young Although Marchant & Higgins (1990) referred to young Australasian Grebes helping feed younger siblings (a behaviour not yet observed in the Grebes at the retarding basin), and Fjeldså (2004) mentioned parent birds separating, each caring for one or two chicks, neither said anything about adult birds other than the parents feeding the young. In this case, whether or not the ‘intruder’ was related to the breeding pair cannot be determined, although it is known that Tachybaptus grebes may leave and return to their natal waterbody; perhaps the third adult had some social bond with the breeding pair, and was accepted for that reason (J. Fjeldså pers. comm.).

The dangerous grille Although several offspring of both Pacific Black Ducks Anas superciliosa and Australian Wood Ducks Chenonetta jubata have fallen through the grille covering the outlet of the retarding basin (pers. obs.), as has happened to ducks elsewhere (Steele 2008), so far this has not happened to any young Grebes, even though they swam near the grille occasionally. In January 2010 a new grille, which should be safe for young birds, was installed (pers. obs). VOL. 27 (3) SEPTEMBER 2010 Australasian Grebe Breeding Behaviour 145

Breeding performance To date, 22 young Grebes have been raised on the retarding basin. Only one nest failed, and that was apparently because of inadvertent human interference. Tachybaptus species can be prolific breeders: a pair of Least Grebes T. dominicus laid 35 eggs in eight clutches and raised 24 young in 10 months (Fjeldså 2004).

Acknowledgements Grateful thanks go to Andrew Ley for considerable help with the manuscript. Jon Fjeldså made valuable comments on a draft.

References Fjeldså, J. (2004), The Grebes, Oxford University Press, Oxford, UK. Marchant, S. & Higgins, P.J. (Eds) (1990), Handbook of Australian, and Antarctic Birds, vol. 1, Oxford University Press, Melbourne. Steele, W. (2008), ‘A cluster of duck deaths at the Western Treatment Plant, Werribee, Victoria, during 2005–06’, Australian Field Ornithology 25, 109–120.

Received 19 June 2009, revised 31 May 2010 