Chatham Island Oystercatcher Recovery Plan 2001–2011
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Chatham Island oystercatcher recovery plan 20012011 THREATENED SPECIES RECOVERY PLAN 38 Published by Department of Conservation P.O. Box 10-420 Wellington, New Zealand © June 2001, Department of Conservation ISSN 11726873 ISBN 047822060X Cover: Chatham Island oystercatcher. (Alan Wright) CONTENTS Recovery plans 4 1. Introduction 5 2. Past/present distribution and population numbers 5 3. Cause of decline and present-day threats 7 4. Species ecology and biology 9 5. Past conservation efforts 10 6. Recovery goal 11 7. Options for recovery 12 8. Objectives for term of plan 13 9. Work plan 13 10. Review date 22 11. References 22 Recovery plans This is one of a series of recovery plans published by the Department of Conservation. Recovery plans are statements of the Departments intentions for the conservation of particular plants and animals for a defined period. In focusing on goals and objectives for management, recovery plans serve to guide the Department in its allocation of resources, and to promote discussion amongst a wider section of the interested public. After a technical report which had been refined by scientists and managers both within and outside the Department had been prepared, a draft of this plan was sent to the Chatham Islands Conservation Board for comment. After further refinement, this plan was formally approved by the Wellington Conservator in January 2001. A review of this plan is due after ten years (in 2011), or sooner if new information leads to proposals for a significant change in direction. This plan will remain operative until a reviewed plan is in place. The Department acknowledges the need to take account of the views of the tangata whenua and the application of their values in the conservation of natural resources. While the expression of these values may vary, the recovery planning process provides opportunities for consultation between the Department and the tangata whenua. Departmental Conservancy Kaupapa Atawhai Managers are available to facilitate this dialogue. A recovery group consisting of people with knowledge of Chatham Island oystercatcher, and with an interest in its conservation has been established. The purpose of the Chatham Island Oystercatcher Recovery Group is to review progress in the implementation of this plan, and to recommend to the Department any changes which may be required as management proceeds. Comments and suggestions relating to the conservation of Chatham Island oystercatcher are welcome and should be directed to the recovery group via the Wellington Conservancy office of the Department. 4 1. Introduction The Chatham Island oystercatcher Haematopus chathamensis is the rarest oystercatcher species in the world. It is endemic to the Chatham Islands, and lives on the rocky coastlines and sandy beaches there. The Department of Conservation presently ranks the CI oystercatcher as Category A, the highest priority category for conservation management (Molloy & Davis 1994). The CI oystercatcher is ranked as Endangered by the IUCN Red List Categories (BirdLife 2000). This plan sets out the recovery programme for CI oystercatcher over the next ten years (20012011). It is preceded by a draft recovery plan (Davis 1989a), and a revised draft recovery plan covering the period 1994 to 1998 (Grant 1993). CI oystercatcher conservation needs were also covered in a management strategy prepared for Chatham Island threatened species (Grant 1991). 2. Past/present distribution and population numbers The historic distribution, including the distribution of CI oystercatchers during the period 1970 to 1989 has been documented by Baker (1973), Best (1987), Davis (1988, 1989b), and Schmechel & OConnor (1999). CI oystercatchers were present in many of the coastal areas of Rangatira, Mangere, Pitt, and Chatham Islands, with a pair being observed during the 1970s on the Star Keys (B. Bell pers. comm.). S. Sawyer (pers. comm.) has observed them more recently on the Star Keys and Murumurus. Best (1987), Davis (1988, 1989b), and Page (1992) recorded the distribution of CI oystercatcher in the late 1980s to early 1990s, and a thorough account of the oystercatchers current distribution in more recent times is available in Schmechel (1999). Figure 1 shows the distribution of CI oystercatcher recorded during the comprehensive census conducted in December 1998. Population surveys of CI oystercatchers carried out between 1986 and 1996 have estimated numbers of oystercatchers to be between 65 and 120 adults, including 3045 breeding pairs (Best 1987; Davis 1988, 1989b; Page 1992; Sawyer 1993, 1994; F. Schmechel pers. comm.). The 1998 survey recorded 142 adult CI oystercatchers, including 34 confirmed breeding pairs (and seven additional suspected breeding pairs). This is 20 to 40 more individual adults than has ever been counted or estimated previously (Schmechel 1999). Best (1987) and Davis (1988) proposed that there had been a decline in CI oystercatcher numbers from the 1970s to the 1980s, based on the loss of oystercatchers from various locations on Chatham Island, and the observed loss of breeding pairs on Rangatira during this period. However, it is debatable whether CI oystercatcher numbers continued to decline until the mid 1990s 5 !"#$"#%&'()#*+&,-($./!#$!"./ !011234&567416804693 Rangitatahi (The Sisters) Kaingaroa Port Hutt Chatham Island Te One TeWhanga Lagoon (Rekohu, Wharekauri) Waitangi Motuhara (The Forty Fours) Owenga Pitt Island Motuhope (Star Keys) Mangere (Rangiauria) Tapuaenuku (Little Mangere) Rangiwheau (The Castle) Rangatira North Island (South East Island) Tarakoikoia (The Pyramid) Chatham Islands South Island Stewart Island N Bounty Is 01020 30 40 km Antipodes Is Figure 1. Distribution of CI oystercatcher in 1998 (after Schmechel 1999). 6 when there was a noticeable increase in CI oystercatcher pairs breeding in northern Chatham Island, or whether, in fact, their population had remained stable in numbers until this time (Schmechel & OConnor 1999). Differences in survey methods used in the last twelve years make it difficult to determine whether the increase in numbers was the result of actual changes in the population or differing survey techniques. A comparison of the number of adult oystercatchers recorded in areas that have been counted most consistently since 1987 indicates a doubling in numbers on northern Chatham Island (and expansion to peripheral areas), an increase on Pitt Island, and decrease on southern Chatham Island and Rangatira. The 1998 census recorded around 66% of birds on Chatham Island, 24% on Pitt Island, and 10% on Rangatira and Mangere Islands. These figures highlight the importance of Chatham Island for CI oystercatchers. At least 58% of oystercatchers recorded during the census were members of breeding pairs (confirmed or suspected territorial pairs), although this is likely to be an underestimate, as many birds were of unknown status. While the 1998 census recorded 3441 oystercatcher pairs (Schmechel & OConnor 1999), more intensive monitoring over the 1999/2000 season indicated that the total breeding population was in excess of 50 pairs (Moore et al. 2000). 3. Cause of decline and present- day threats Five factors appear to be threatening the CI oystercatcher population and have led to its endangered status (Davis 1988; Grant 1993; F. Schmechel pers. comm.). 3.1 PREDATION Cats, rats, hedgehogs, pigs, weka, black backed gulls, harriers, and possums are potential predators of CI oystercatcher eggs and young chicks, with cats also possibly preying on adults. Video work in 1999/2000 in the north of the Chathams recorded three predation events on film (2 cat, 1 weka) and several close calls of predators sniffing or handling eggs, or nearly trampling nests (cat, weka, harrier, possum, sheep, cattle, human) (Moore et al. 2000). In addition, predation by skuas takes place on Rangatira, Mangere, and Pitt Island during the breeding season, and predation by gulls has been observed on Rangatira (A. Davis pers. comm.). Spur-wing plover were suspected of preying on a clutch of CI oystercatcher eggs on Chatham Island (F. Schmechel pers.comm.). 7 3.2 HABITAT MODIFICATION Changes in coastal vegetation appear to have had an adverse effect on oystercatcher breeding in northern locations on Chatham Island. In sites where marram (Ammophila arenaria) has established, the beach profile has become steeper and the dune face has moved closer to the high water mark than occurs where dunes are covered in native dune vegetation. CI oystercatchers prefer to nest in more open areas, and the establishment of marram appears to have forced the oystercatchers to nest further down the beach where the likelihood of losing nests to spring tides or storm surges is greatly increased. Marram also creates a relatively dense vegetation cover that can conceal predators approaching the oystercatcher nests. 3.3 NATURAL DISASTERS CI oystercatcher nests are vulnerable to spring tides and storm surges. Losses from natural events become significant when combined with nest losses from human-induced causes. Inundation of nests was the most significant cause of nest loss among CI oystercatchers breeding on northern Chatham Islands during the 199497 breeding seasons (Schmechel 1998) and in 1998/99 (Bell 1999, OConnor 1999). These losses are probably linked to habitat modifications where the dense marram growth appear to have forced the oystercatchers to nest further down the beach than they would otherwise. 3.4 DISTURBANCE CI oystercatchers are sensitive to disturbance during nesting. When nesting birds