Chatham Oystercatcher Haematopus chathamensis Scientific name definitions

47–49 cm; male averages 540 g, female 640 g. Black frontal coloration extends well down breast , and transition to white lower breast is mottled, both features also found in pied morph of <em>H. unicolor</em> , but in no other Old World pied oystercatcher. Most closely resembles pied morph of H. unicolor, but averages slightly smaller with much shorter bill ; legs and feet  stockier; in flight, white uppertail-coverts less conspicuous. Distinguished from H. palliatus by red, not yellow, eye and black, not blackish-brown, dorsal coloration; from H. leucopodus by red, not yellow, eye and mostly black secondaries. Female similar to male, but averages larger and longer-billed. Juvenile  has brown fringes to feathers of upperparts, and dull bare-part colours.

Mostly found on rocky shores, less often on sandy or gravel beaches; sometimes nest  in sites with some short vegetation. Previously, it appeared that the species only bred in areas composed entirely or partly of volcanic rock platform, but successful breeding now also occurs on sandy beaches (3 Dowding, J. E., and E. C. Murphy (2001). The impact of predation by introduced mammals on endemic shorebirds in New Zealand: a conservation perspective. Biological Conservation 99(1):47–64. Close ).

Mostly sedentary and territorial throughout the year; juvenile dispersal up to 40 km between islands.

Prey includes the anemone Isactina tenebrosa, an unusual prey type for oystercatchers; also polyplacophorans (Chiton pelliserpentis, C. glaucus), gastropods (Haliotis australis, H. iris, Cellana chathamensis, Patelloidea corticata, Zelidoma digna and several others), bivalves (Aulacomya maoriana, Mytilus edulis, Xenostrobus pulex), barnacles, isopods, echinoderms and ascidians. Rocky shores favoured for foraging. All oystercatchers attack different prey types using variety of techniques , e.g. hammering, prising, probing , stabbing.

Most-frequently heard call a repeated over-slurred piping whistle “peep” or a doubled “pi-peep”. Also a shorter and softer “puk”. Display call initiated with a piping trill that increases in volume and leads into several doubled notes, “prrrrrr-pi-pi-pipeek-pipeeek-pipeeek” (the doubled notes apparently more strident and piercing than H. unicolor). In groups, several birds may call simultaneously, typically resulting in a loud continuous piping. Overall quite similar to other members of the genus.

Breeds Oct–Mar, with most laying Oct–Dec. Nest  a scrape in ground, lined or unlined; often in sheltered site under overhanging rock or vegetation (e.g. Olearia traversii), sometimes in small cave or on cliff ledge, once c. 6 m deep within a cave and 1·5 m above ground on a ledge within it (4 Young, E.C. (2002). Shorebird numbers and nesting habits on the Chatham Islands. Notornis. 49(3): 166–174. Close ). Clutch size 2  –3; three-egg  clutches commonest early in breeding season; incubation  c. 25 days. Chick  has heavily speckled grey upperparts  ; tail has conspicuous white subterminal band. Fledging period 46–49 days. Fledging success 0·20–0·85 (0·47) young per pair per year on (predator-free) Rangatira, with breeding productivity on Chatham I, where introduced predators are present, improving due to conservation action in some areas (see Status and Conservation), thus in 1999–2001 chicks fledged from 39% of managed eggs, versus just 6% of eggs in unmanaged areas, while annual success in N Chatham I increased from 0·1–0·9 fledged chicks/pair, before 1998, to 0·5–1·6/pair in 1998–2004 (5 Moore, P.J. (2008). The recovering population of the Chatham Island oystercatcher (Haematopus chathamensis). Notornis. 55(1): 20–31. Close ). Annual adult (88%) and juvenile (48–68%) survival similar to other Haematopus, based on data from 1970s and 1980s (5 Moore, P.J. (2008). The recovering population of the Chatham Island oystercatcher (Haematopus chathamensis). Notornis. 55(1): 20–31. Close ). Mean lifespan c. 8 years, with the oldest recorded bird at least 28 years old.

ENDANGERED. Population increased from c. 50 birds in early 1970s (of which almost half were on Rangatira) to 100–110 birds in breeding season of 1987/88, including 44 pairs, to 142 individuals in Dec 1998, including 34–41 pairs (6 Schmechel, F.A. and O’Connor, S. (1999). Distribution and abundance of the Chatham Island Oystercatcher (Haematopus chathamensis). Notornis. 46(4): 155–165. Close ), and most recently 313–351 birds in 2006, including 109 pairs, although there are still fewer than 250 mature individuals (5 Moore, P.J. (2008). The recovering population of the Chatham Island oystercatcher (Haematopus chathamensis). Notornis. 55(1): 20–31. Close ), and latest information indicates that the population has levelled off and that Chatham I has reached carrying capacity. As long ago as 1860s, the species was considered to be uncommon (5 Moore, P.J. (2008). The recovering population of the Chatham Island oystercatcher (Haematopus chathamensis). Notornis. 55(1): 20–31. Close ). Largest numbers on Chatham I during all of the more recent surveys, including 25 pairs in 1987/88, 23–30 pairs in 1998 and c. 200 individuals in 2005/06, where species has obviously increased and expanded its range over the last two decades; eight pairs on Pitt in 1987 (then ten in 1998 and 13–15 pairs in 2004–2006) (5 Moore, P.J. (2008). The recovering population of the Chatham Island oystercatcher (Haematopus chathamensis). Notornis. 55(1): 20–31. Close ), eight on Rangatira (but just 3–4 in mid 2000s) (5 Moore, P.J. (2008). The recovering population of the Chatham Island oystercatcher (Haematopus chathamensis). Notornis. 55(1): 20–31. Close ), two on Mangere (three in 2009); possibly one pair on nearby Star Keys, which was not surveyed in 1998. Main threat is predation by introduced cats (Felis catus), rats (Rattus exulans, R. norvegicus and R. rattus) and Wekas  (Gallirallus australis), with domestic dogs (Canis lupus familiaris) and Red-billed Gulls (Larus novaehollandiae scopulinus) also responsible for some losses (5 Moore, P.J. (2008). The recovering population of the Chatham Island oystercatcher (Haematopus chathamensis). Notornis. 55(1): 20–31. Close ); within range, only Rangatira I and Mangere I are predator-free, and both have been designated nature reserves since 1950s; in parts of range grazing mammals also have negative effects on species, while predation by Brown Skuas (Catharacta antarctica) may be another significant factor. Human disturbance is also a problem; access has been prohibited to a section of coast of Rangatira, in order to reduce level of disturbance. On Chatham I, some pairs nesting on sandy beaches are forced down towards seashore by introduced maram grass (Ammophila arenaria), where nests more vulnerable to flooding during storms or high tides; since 1992, conservation efforts  to avert this by moving nests further in from sea, intensive predator control and artificial incubation of eggs, for return immediately prior to hatching, is probably contributing to reduce risk of predation. Following relative success of this work on Chatham, attention started to shift to Pitt I in 2005/06, where breeding success was then very low (5 Moore, P.J. (2008). The recovering population of the Chatham Island oystercatcher (Haematopus chathamensis). Notornis. 55(1): 20–31. Close ).