VOL. 17 (8) DECEMBER 1998 383

AUSTRALIAN WATCHER 1998, 17, 383-389

Four-egg Clutches in the Hooded : Description, Occurrence and Female Investment

by M.A. WESTON!, A.J. BURKP, V.L. FORD2 , J.D. STEWARP, and B. DOWLING4 •

'Department of Zoology, University of Melbourne, Parkville, Victoria 3052 2Friends of the Hooded Plover, c/- Momington Peninsula National Park, P.O. Box 117, Sorrento, Victoria 3943 3Box 28, Rendelsham, South Australia 5280 4Momington Peninsula National Park, P.O. Box 117, Sorrento, Victoria 3943

Summary We describe five nests of the Hooded Plover, from Tasmania, Victoria and South Australia, each of which contained four eggs. Clutches of four eggs are rare, but have been recorded from all major types of habitats except inland wetlands. At least some eggs are known to have hatched in the four­ egg clutches that were monitored, though only one was known to hatch all four chicks; only one nest produced fledglings. The proportion of female body weight represented by the eggs in the clutch, a crude measure of female investment, indicated that four-egg clutches did not represent an unusually high investment in comparison with the normal investment made by other species of in Australasia. Introduction The breeding biology of the Hooded Plover Thinornis rubricollis is considered to be reasonably well known (Marchant & Higgins 1993). Nevertheless, many aspects of breeding remain poorly known, particularly those that are cryptic or rare. Nests can be difficult to find, and little has been published on basic breeding parameters, such as clutch-size. The Hooded Plover shows considerable variation in clutch-size, with clutches consisting of between one and four eggs (Marchant & Higgins 1993). This note serves to describe five known instances of clutches containing four eggs, and place them in context in terms of frequency of occurrence. We also compare the female investment by Hooded Plovers in clutches containing four eggs with that of other plovers breeding in the region. In the literature, there appears to be only one paper that mentions a clutch of four eggs: Stewart (1991); and a single unnumbered plate in South Australian Ornithologist [Vol. 12(1), 1933]. There are other records of four-egg clutches, but they are all unpublished. They refer to nests in Victoria and Tasmania, including one on Flinders Island, in Bass Strait (P. Park & M. Schulz pers. comm.). Full details of these records are unavailable, and so will not be discussed further. It is also possible that other unpublished records of large clutches exist. We are not aware of any clutches containing more than four eggs, either reported in the literature, from our own observations, or known to other workers (P. Park & M. Schulz pers. comm.). Methods This report summarises data collected in south-eastern South Australia (by J.D. Stewart), and the Mornington Peninsula (B. Dowling), and. other areas in Victoria (M.A. Weston). All researchers have regularly searched for and checked nests, and systematically recorded clutch-size. In addition, we have searched relevant published reports of breeding biology for clutches containing four eggs, and analysed the Australia Nest Record Scheme (NRS) database. We have also questioned other researchers working on Hooded Plovers (B. Baird, T. Dennis, P. Park). The exact localities of the nesting sites have been withheld for their protection. AUSTRALIAN 384 WESTON et a!. BIRD WATCHER

Potential problems in the determination of clutch-sizes There are two problems with the determination of clutch-size: the possibility that laying has not yet been completed, and the possibility of partial loss of the clutch. Both of these problems will cause clutch-sizes to be underestimated. If nests are checked during the laying period, clutch-sizes will be underestimated unless they are re-ch~cked after an appropriate delay; in Hooded Plovers this needs to be at least two days (Newman & Park 1992, M.A. Weston unpubl. data). The clutch-sizes for Hooded Plovers reported here were collected by experienced researchers who usually re-checked nests, and usually determined that laying had been completed. There is also the possibility of partial loss of a clutch during incubation, which has been recorded in Hooded Plover nests in both South Australia and Victoria (unpubl. data). The contents of a nest containing three eggs in the Momington Peninsula National Park decreased by one egg per day, and footprints indicated that this was the result of partial crushing by humans (unpubl. data). Single-egg clutches in the New Zealand Dotterel Charadrius obscurus have been attributed to predation of other eggs in the clutch (Marchant & Higgins 1993), though it is unclear whether the eggs were taken during laying, causing a shift in the nest-site before subsequent laying, or if only some eggs were taken from a particular nest. There is a record in the NRS that has attributed a clutch of one egg to a pair whose behaviour is very suggestive of the presence of chicks; this would mean that the one remaining egg was probably addled, and one or more chicks were hidden nearby.

Potential problems in the interpretation of large clutch-sizes Unusually large clutches in plovers (e.g. six eggs in the Double-banded Plover Charadrius bicinctus and Shore Plover 1hinomis novaeseelandiae, four eggs in Anarhynchusfrontalis) are attributed to laying by two females in the same nest; often, variation in pigmentation between eggs in a clutch is given as evidence of laying by more than one female (see Marchant & Higgins 1993). Although there is occasionally great variation in pigmentation between eggs within Hooded Plover nests, there is no evidence of egg-dumping, despite significant study including over 500 hours of nest observation, and nests that were monitored by an electronic system which allowed the individual identification of many potential non-pair visitors to the nest (unpubl. data). There have been occasional observations of extra-pair adults near nests with eggs, at nests both on beaches and in dunes (unpubl. data), and so the possibility cannot be absolutely excluded. Any extra-pair maternity (apart from egg-dumping) would still involve the female laying the clutch. Realistically, it is impossible to determine the number of females contributing to a clutch without genetic analysis (DNA fingerprinting) of the eggs and attendant adults. No genetic analysis of egg maternity was conducted.

Potential problems with interpretation of brood-sizes It may be possible to retrospectively assign the size of a clutch by determining brood-size, but we do not consider that this is a reliable approach, as partial brood loss is common (Weston 1998). We have never recorded any amalgamation of broods involving non-flying young, but colour-banding has revealed that groups of flying juveniles are not necessarily related. Brood 'capture' has been recorded in a number of species, e.g. Little Stint Calidris minuta (T.V. Sviridova pers. comm.). Both adults usually attend young chicks, and, in some other territories, single adults have been seen brooding three chicks (unpubl. data), with two chicks under one wing. VOL. 17 (8) DECEMBER 1998 Hooded Plover - Four-egg Clutches 385

Therefore, it is possible for a single adult to brood four chicks, with two under each wing, at least while the chicks are small. Some migratory , such as the Little Stint and Curlew Sandpiper C. ferruginea, often brood four chicks in their Siberian breeding grounds (M.A. Weston pers. obs.). We have one noteworthy record of a group of two adults and four juveniles in south-eastern South Australia, made by R. Schleter while conducting a regular Hooded Plover survey on 2 December 1989. It was noted that the young birds were not runners. The temptation is to interpret such a record as a pair of adults with four of their young. However, there is no independent evidence to suggest that the young originated from the same breeding pair, or to determine any other relationships between members of the group (e.g. whether the adults were even related to any of the juveniles). Therefore, we do not accept such observations as strong evidence of either brood- or clutch-size.

Results We located records of five clutches of four eggs from our data and from the NRS. They were recorded from beaches and coastal dunes. The records of four-egg clutches originated from three states and all of the four-egg nests that were satisfactorily monitored are thought to have hatched at least one chick. Only one is known to have hatched all four chicks, and only one is known to have fledged young.

South Australia (1) This nest was found in the Cullens Bay area, in the Canunda National Park, on 6 November 1990, and has been previously described (Stewart 1991). The nest was in a dune, about 500-600 m from the nearest beach. This pair escorted its chicks to the nearby beach, where three chicks were seen on 7 December. (2) This nest was discovered by S.E. Stewart in the Canunda National Park on 4 January 1997. The nest was on a rocky rise about 150m from the beach. This pair escorted its chicks to the nearby beach, and a dead chick was found there on 19 January. (3) This nest was discovered by I. D. Stewart, in the company of S. Gilbert and D. Gollan (S. A. Dept of Environment & Natural Resources) on 26 November 1997. The nest was on the ocean beach in The Coorong, south of the mouth of the Murray River. It was about 2 m below the fore-dune, on the upper part of the beach. A large piece of cuttlefish was on one edge of the nest-scrape. Only one visit was made to this nest, so its fate remains unknown.

Victoria ( 4) A single nest was discovered at a popular ocean beach in the Moroington Peninsula National Park by V.L. Ford and A.J. Burke. The nest, containing three eggs, was found on 10 December 1997, and four eggs were seen in the nest on 24 December (Plate 62). It was situated on a flat area above a low cliff, which consisted of calcarenite with a little sand and unconsolidated material, and also some calcarenite rubble and other rocks. The nest contained small fragments of shells, which is not unusual, but there was an unusually large amount of shell material at the nest (B. Baird pers. comm.). All the eggs hatched, and four chicks were seen on 9 January 1998. This nest had the only four-egg clutch where all four eggs are known to have hatched. The chicks and adults subsequently moved to the beach. A check about 14 days after hatching revealed only two chicks. These chicks both fledged, and this is the first record of successful fledging from a nest containing four eggs. The loss of chicks is not unusual, though the causes AUSTRALIAN 386 WESTON et al. BIRD WATCHER

A Hooded Plover nest containing four eggs, showing unusually large amount of nesting material (shells), arrangement of eggs, and placement of nest. Plate 62 Photo: A.J. Burke

are practically unknown (Weston 1998). We do not know the fate of the lost chicks, but it was not necessarily related to the unusually large size of the brood.

Tasmania (5) This nest was described on a NRS data sheet completed by J. Harris. On 28 October 1992, a clutch of four eggs was discovered at Death Valley Beach on the north­ eastern coast (40°45'S, 148 °08'E). The nest had disappeared when a return visit was made on 5 November, but the observer considered that the eggs had hatched, and young were subsequently seen. Although the sheet records four young, an attached comment indicates that this was an inference, and that the young had not been sighted. Follow-up visits revealed only two young.

Occurrence of four-egg clutches Clutches containing four eggs are very rare. Their occurrence in different areas is shown in Table 1. In addition to our data (n=273 nests), the NRS contains data on nests from throughout the range of the Hooded Plover. When the account in Marchant & Higgins (1993) was prepared, there were only 34 nests recorded in the database, and none contained a clutch of four eggs. There are now 169 records of Hooded Plover nests in the database: of the 136 records that adequately recorded clutch-size, only one nest contained four eggs (0. 7% of all records). Regular monitoring on Phillip Island, Victoria, has revealed no nests containing four eggs, although about 80 nests have been located (B. Baird pers. comm.). Although the NRS database contains records from throughout the range of the Hooded Plover, only 11 are from Western Australia. Notwithstanding the inherent VOL. 17 (8) DECEMBER 1998 Hooded Plover - Four-egg Clutches 387

Table 1

The occurrence of four-egg clutches in Hooded Plovers. All data were gathered by the authors, except those from Western Australia, which were extracted from Newbey (1996). Western South-eastern Cape Otway Mornington Kilcunda to Australia South to Point Peninsula, Wilson 's Australia Lonsdale, Victoria Promontory, Victoria Victoria Total number of nests located 13 42 74 86 71 Number of four-egg clutches located/reported 0 3 0 0 Percentage of nests with four-egg clutches 0.0 7.1 0.0 1.2 0.0 80 70

Ul"" 60 -Cll c .... 50 0 Cll Cl 40 :1 c 30 Cll ..u Cll 20 0. 10 0 2 3 4 Clutch-size

Figure 1. The occurrence of different clutch-sizes in the nests of Hooded Plovers (n = 136 records in Nest Record Scheme, where clutch-size was determined on at least two dates). error in determination of clutch-sizes, the frequency distribution of different clutch­ sizes in the NRS is given in Figure 1. The average clutch-size in the NRS was 2.7 eggs (n = 136). Four-egg clutches were the least frequently recorded clutch-size. Two­ egg and three-egg clutches were most common, accounting for 97 % of all nests in the database. Clutches with three eggs were more common than two-egg clutches (x.Z=31.03, p(0.01). In summary, when we combine our data (n =273 nests, not yet added to the NRS database), with those nests in the NRS where clutch-size has been determined (n= 136), we found c. 1.2% of all nests had clutches of four eggs.

Discussion Clutches containing four eggs are rare. Table 2 shows the typical clutch-size in plovers (Charadriinae) that breed in Australia and New Zealand; in addition, the Red­ kneed Dotterel Erythrogonys cinctus (Vanellinae) is included. None of the Charadriinae that breeds in Australia has a modal clutch-size of four eggs, though six species have Table 2 w 00 Selected breeding statistics of plovers (and the Red-kneed Dotterel) that breed in Australia and New Zealand, based on data in Marchant I 00 & Higgins (1993). The highest egg weights have been taken, because eggs lose weight during incubation (see, for example, Saunders & Smith 1981). Where sexual size dimorphism may not have been uncovered, data from both sexes have been pooled. As weight may vary seasonally, this table represents approximate measures of female investments; maximum, rather than average weight has been used in order to make estimates as conservative as possible. Species Variation in Range Modal Egg weight Adult female Proponion of female clutch-size (usual) clutch size (g) weight (g) body weight in an (no. of eggs) average clutch New Zealand Dotterel Charadrius obscurus 1-6 5 3 23.7 124.0 0.57 :E til Red-capped Plover en >-3 C. ruficapillus 1-4 3 2 8.4C 54.0 0.31 0 Double-banded Plover z C. bicinctus 2-6 4 3 12.0 76.0 0.47 ~ ~ Inland Dotterel C. australis 2-4 2 3 - 107.0 Black-fronted Dotterel Elseyonis melanops 1-4 3 2-3 - 42.0b Hooded Plover 1hinomis rubricollis 1-4 3 3 14.0 110.0b 0.38 Shore Plover T. novaeseelandiae 2-3• 1 3 14.5 69.0b 0.63 Wrybill Anarhynchus frontalis 1-3 2 2 11.4 64.8 0.35 td Red-kneed Dotterel -tic:~> Erythrogonys cinctus 1-5 4 4 - 54.0 - :Ecn >>-3 "one clutch of six excluded as it was definitely known to have resulted from laying by two females. nr>-3~ bdata pooled from both sexes. ::r:- cbased on five eggs, all known to be less than 7 days old, from Truganina Swamp, Altona, Victoria. Minimum egg weight was 6 g, and the til> eggs averaged 7 g; length ranged from 28.6 to 30.6 mm and width ranged from 21.0 to 23.7 mm. ~z VOL. 17 (8) DECEMBER 1998 Hooded Plover - Four-egg Clutches 389

maximum recorded clutch-sizes of at least four eggs. Despite the modal clutch-sizes in Australian Charadriinae invariably being two or three eggs, the ratio of weight of eggs: weight of female (a crude measure of female investment in a clutch) varies considerably between species, and might reflect differences in the breeding strategies. Several species are excluded from the calculation of female investment, due to the unavailability of egg weights from the literature (Marchant & Higgins 1993) or other sources, such as the Museum of Victoria (R. O'Brien pers. comm.). This comparison is preliminary because we have not controlled for phylogeny, and have confined our comparisons to the Australasian region. When compared with other plovers (except the Wrybill and Red-capped Plover), female Hooded Plovers contribute relatively little (in terms of the proportion of female body weight) to an average clutch. A clutch containing four eggs would probably represent about 56% of the average female body weight (and 51% of maximum female body weight), which is lower than the investment the congeneric Shore Plover makes in an average clutch. So, perhaps, the real question is: why don't Hooded Plovers usually, or at least more frequently , lay four-egg clutches?

Acknowledgements This is the first publication bringing together the observations of various Hooded Plover researchers. This is particularly useful where we deal with rare or unusual phenomena, and our combined data allow us to provide useful contextual information. It is hoped that further co-operative publications will follow. We thank R. Poulter for his expertise and help with the Birds Australia Nest Record Scheme, and J. Peter, P. Dann and M. Schulz for useful suggestions and comments. Funding agencies supporting the various researchers were: Coast Care, the S.A. Department of Environment & Natural Heritage, Holsworth Wildlife Research Fund, Stuart Leslie Research Fund, Ingram Trust, Barwon Heads Committee of Management, and the Australian Bird Environment Foundation. Numerous people have helped, and we should like to thank the Stewart family, the Friends of the Hooded Plover (Mornington Peninsula), B. Baird, P. Park, T. Dennis, S. Gilbert and D. Gollan.

References Marchant, S. & Higgins, P.J. (Eds) (1993), Handbook of Australian, New Zealand and Antarctic Birds, vol. 3, Oxford University Press, Melbourne. Newbey, B.J. (1996), 'Report on Hooded Plover project', Suppl. to West. Aust. Bird Notes 70. Newman, O.M.G., & Park, P. (1992), 'Egg laying interval: Pied Oystercatcher and Hooded Plover', Stilt 20, 22-23. Saunders, D.A. & Smith, G.T. (1981), 'Egg dimensions and egg weight loss during incubation in five species of cockatoo, and the use of measurements to determine the stage of incubation of birds' eggs', Aust. Wildlife Research 8, 411-419. Stewart, I.D. (1991), '1990 spring Hooded Plover survey, South Australia', Stilt 19, 9- 10. Weston, M.A. (1998), ' takes Hooded Plover chick' , Aust. Bird Watcher 17, 266- 267 . Received 2 7 May 1998 •