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https://doi.org/10.24199/j.mmv.1981.42.05 30 September 1981 DISTRIBUTION AND STATUS OF COASTAL COLONIES OF SEABIRDS IN VICTORIA By M. p. Harris* and F. 1. NormanI *Instilule of Terrestrial Ecology, Banchory Research Station, Hill of Braihens. Glassel, Banchory, Kincardineshire AB3 4BY, U.K. tArthur Rylah Institute for Environmental Research, Fisheries and Wildhfe Division, Ministry for Conservation, 123 Brown Street, Heidelberg, Victoria 3084. Abstract Most of the known seabird colonies around the Victorian coast were surveyed between October and December 1978; others were examined in 1979 and early 1980. Data collected included colony area, nest- site density, associated vegetation and soil depth. There were some 1.45 milHon burrows of Short-tailed Shearwaters Puffinus lenuirostris in Victorian colonies and about 20 000 nest sites of Little Penguins Eudyptula minor, the two most abundant species encountered. Earlier estimates of colony numbers or size are reviewed together with survey estimates and the individual species' status is considered and com- pared with other Australian data. The threats to breeding areas and to the species in Victoria are considered. Most Victorian seabird colonies are currently secure although some breeding sites are being reduced by land development. Man's increasing use of the coast, and the associated increased predation by dogs, may be locally severe but is of little importance to populations generally. Oil spills and other pollutants present potential threats and possible competition between seabirds and the local fishing industry requires investigation. Introduction (June); Rabbit (December). Wattle Island was In a changing environment conflict between surveyed in December 1979 and Dannevig and Norman Islands were visited in 1980. the requirements of man and those of wildhfe is January inevitable. As well as killing or hunting wildlife A few of the smaller islands for which recent details were available investigated, of all types for food or sport, man affects were not nor wildlife indirectly by removing or modifying were the more inaccessible stacks in the Bay of habitats and by introducing detrimental Islands Coastal Park and the Port Campbell substances. Consequently populations of ani- National Park. Mainland colonies of some species also visited, the mal groups such as seabirds may alter were but data collected dramatically. In Austraha there have been a are incomplete. Data from pubUshed and un- published sources few attempts to assess the sizes of breeding have been incorporated colonies of seabirds comparable with those con- below. In this survey we consider the following species in detail: ducted in Britain and Ireland (e.g. Cramp, or (e.g. Bourne and Saunders, 1974) Canada Little Penguin Eudyptula minor Nettleship, 1977) but recently some accounts of Fairy Prion Pachypiila turlur Short-tailed Shearwater lenuirostris island seabird colonies have been published (in Puffinus White-faced Storm Petrel Pelagodroma marina the Australian Bird Bander and its successor Common Diving-Petrel Pelecanoides urinafrix the Corella). However, such details are Australasian Gannet Morus serrator Black-faced Shag Leucocarbo fuscescens generally lacking for Victorian colonies. Silver Gull Larus novaehollandiae The present study was designed to produce Pacific Gull Larus pacificus data against which subsequent changes may be Kelp Gull Larus dominicanus Caspian Tern Hydroprogne caspia evaluated, and from which management pro- Crested Tern Sterna bergii cedures may be formulated to retain 'desirable' species at appropriate levels. Techniques for the estimation of seabird Methods populations, and the accuracy of such Between October and December 1978, at- estimates, depend largely on the species in- tempts were made to visit the larger coastal volved. Methods used tend to be group-specific islands of Victoria (Figure 1). Some islands and vary from direct counts (of nests, or pairs, were also revisited in 1979; Lady Julia Percy or eggs, etc.) to sampling segments of colonies (January); Citadel (February); South Channel and extrapolation of areas occupied. For bur- Memoirs of the National Museum Victoria, 89 No. 42, !98L G2 90 M. P. HARRIS AND F. I. NORMAN 39 40 38 9^ / 13-7 Tvi2 3' 4' 10 / \ \~^^ ,/ \ » ^Hi^ a<y 1^ V Point Dar>9er Prench (sland 21 Wilsons Promontory 31 Wattle Islond Lawrence Rocks Tortoise Head 22 Shellback Islond 32 Rabbit Rock Lody Julia Percy Island Phillip Isbnd 23 Norman Island 33 Rabbit Isbnd Grifhthi (sktnd Seal Rocks 24 Great Glennie Islond 34 Rag Isbnd Me>n Island The Nobbies 25 Donnevig Islond 35 Cliffy Islond Middle Island Cape Woolamoi 26 Citadel Island 36 Notch Island Bay of Islands Corner Inlet 27 Mc Hugh Island 37 Seal Island Wedge Light Granite Island 2& Anser Island 38 The Skerries Mud Islands 19 Benison Island 29 Cleft Island 39 Tulbburga Island -i^ South Channel Isbnd 20 Doughboy Island 30 Konowna Island 40 Gobc Island Figure 1 . Main localities mentioned in text. rowing species particular problems exist with drawings. However, areas of small colonies temporal variation in occupancy, burrow den- were determined by ground measurement. sity (which can be materially affected by Because no allowance was made for irregular substrate) and burrow or colony distribution. topography the areas of many colonies were Additionally, the identification and numerical slightly under-estimated. determination of nest sites themselves may be In small colonies, the numbers of burrows difficult or impossible in certain terrain (for showing signs of current usage were counted further details see Nettleship, 1976). The tech- directly. Elsewhere burrow density was deter- niques used in this survey are discussed below: mined by counting burrows in circular quadrats time and weather constraints added to other of 20 m2. In the larger colonies (e.g. Cape practical problems. Survey information is sum- Woolamai), and in those with prominent marised in Appendix 1, and further, more features (e.g. Griffiths Island, Corner Inlet descriptive, details may be found in the series of islands), the quadrats were selected by means of articles on individual islands published mainly a numbered grid, superimposed on a map or in Corella (and hsted in the references) or in photograph of the colony, and tables of ran- Harris (1979), as may earlier information on dom numbers. In some colonies the quadrats the islands. sampled were at irregular intervals of 5-10 m, Existing or potential threats to colonies were along a zig-zag path from one side of the colony recorded. Whilst human disturbance may affect to the other. The position of the quadrat was all seabird colonies only observed instances are determined by throwing a metal rod about 5 m listed below. ahead. Quadrats which covered bare rock were always included. Total numbers of SHORT-TAILED SHEARWATER burrows in colonies were determined from the product of The boundaries of colonies usually coincided colony area and mean burrow density; 95% with changes in vegetation and were marked on confidence Umits are ± 2 SE of the mean den- local maps or aerial photographs (black and sity. Most nest sites had only one entrance but white or colour) of largest available scale. some had several; how this affects estimates of Larger colonies were subdivided, where prac- breeding pairs is not known. No allowance is ticable, according to vegetation or physical made for possible error in delineation of colony features, and areas determined from the scale boundaries. SEABIRD COLONIES 91 For most Short-tailed Shearwater colonies OTHER SPECIES samples of burrow density were sufficient to On most islands Fairy Prion and Common provide reasonably restricted 95% confidence Diving-Petrel burrows were difficult to find and limits (given as ranges below). The accuracy of impossible to census, hence the population sizes such estimates is unlikely to be greatly increased of each colony are only general impressions. since some quadrats always contain no Nests of Australasian Gannets were counted, as burrows. However, the largest source of error were those of gulls and terns where practicable. was in determining the areas of colonies: in When gull colonies were inaccessible the low-density colonies with scattered, outlying number of pairs holding territories was burrows boundaries were particularly difficult estimated and added to counts of nests. to delineate. Replicate counts were not made, but inter- On 1 November 1978, before laying, 56 observer differences were minimised since all burrows on PhilHp Island were individually counts in 1978 were made by the senior author. marked; on 22 December 46 (82%) held eggs. A further 150 burrows were examined on Great Glennie Island (7-11 December 1978); these Results held 98 eggs (e.g. 65%). Burrows were also ex- L ISLAND/COLONY DETAILS amined on Wattle Island (12 December 1979; Survey dates, methods and results (including 50, 34 occupied). population estimates) are summarised in Ap- pendix 1 for the individual islands examined and totals for Little Penguins and Short-tailed LITTLE PENGUIN Shearwaters given in Table 1. Details for other The above procedure was generally adopted colonies (not surveyed) are as follows: in penguin colonies, but only burrows with adults, young, eggs or accumulations of drop- Skull (Cleft) Island pings were counted. Because burrow densities Black-faced Shags recently bred on the island in colonies among rocks, or in thick vegetation (Lane, 1979b) and burrowing species may nest (where there tended to be few), were difficult to in the apparently sparse vegetation. estimate, the numbers of burrows in the more Killarney Reef accessible areas of such colonies were deter- Some 500 pairs of Silver Gulls and about 200 mined and extrapolated to provide estimates of pairs of Crested Terns have been recorded as burrow densities. However, on some islands nesting (Bowker, 1980a). even this proved impossible and only the order of magnitude of burrow densities is proposed Bay of Islands below. Hundreds of Short-tailed Shearwaters were Conversion of number of burrows to number seen on a stack off Boat Bay in about 1960 (W.