Ornithol. Sci. 2: 89–96 (2003)
INVITED ARTICLE Translocations in avian conservation: reintroduction biology of the South Island Saddleback (Philesturnus carunculatus carunculatus)
Johanna P. PIERRE#
Marine Conservation Unit, Department of Conservation, P. O. Box 10–420, Wellington, New Zealand
Abstract Translocation is a commonly used tool in conservation management. ORNITHOLOGICAL However, because post-release monitoring has been infrequent in the past, reasons for SCIENCE the outcomes of translocations have often been unknown. Here, I review the reintro- © The Ornithological Society duction biology (including dispersal patterns, social organisation, survival, habitat use of Japan 2003 and foraging patterns) of a population of 26 South Island Saddlebacks (Philesturnus carunculatus carunculatus), on Motuara Island, New Zealand. After release on Motu- ara Island, South Island Saddlebacks dispersed widely through forest areas. During their first post-release breeding season, saddlebacks established territories of 1.9 ha- 8.8 ha (X¯ 4.21 ha, SD 2.42) in size, and territorial confrontations were very rare. Saddlebacks bearing both adult and subadult plumage held territories and attempted to breed, and successful breeding produced approximately 10 fledglings. Saddlebacks foraged on a variety of plant species, dead wood and the ground. Except for five-fin- ger (Pseudopanax arboreus), a preferred foraging substrate, birds foraged in all plant material in proportion to its availability. Saddlebacks preferred to forage in the lower levels of the forest. Although vegetation composition differed significantly between territories, all territories contained forest areas, and birds appeared to prefer foraging in larger sized trees. Large territory sizes, breeding attempts by young birds and rarity of territorial confrontations are most likely products of low population density. As density increases, birds are expected to occupy smaller territories, forage more effi- ciently within these smaller areas, start breeding at older ages, and possibly colonise scrub habitats. The translocated group sustained no more than 50% mortality at 8-10 months after release. In the past, translocations of 15–59 South Island Saddlebacks have been successful, suggesting that the relatively small founder group does not threaten the success of the transfer to Motuara Island. Saddlebacks are flexible in their habitat use, appear to readily adapt to ‘new’ environments and have high repro- ductive potential, increasing the likelihood of success of translocations of this species.
Key words New Zealand, Philesturnus carunculatus carunculatus, Reintroduction, South Island Saddleback, Translocation
Translocation is becoming increasingly commonly 1973; Merton 1973, 1975; Bell 1978; Butler & Mer- used for conservation, and can be defined as the in- ton 1992). In New Zealand, translocations have often tentional release of plants or animals to the wild been incorporated into species management programs to establish, re-establish or augment a population in the past, and have been successful in saving some (IUCN 1987; Griffith et al. 1989). The technique has New Zealand birds from extinction. Since the 1880s, been applied to the conservation of mammals (e.g. almost 400 translocations of 50 taxa (42 birds, five Dufty et al. 1994; Short et al. 1994), invertebrates reptiles and three invertebrates) have been conducted (e.g. Sherley 1994) and birds (e.g. Atkinson & Bell in New Zealand, often in emergency situations, such as in 1962 when ship rats (Rattus rattus) arrived at (Received 4 March 2003; Accepted 23 September 2003) the last stronghold of the South Island Saddleback # E-mail: [email protected] (Philesturnus carunculatus carunculatus) (Atkinson Proceeding of the Symposium on Behavioral Studies and Conserva- tion Biology. 15 September 2002, Tokyo; Organized by Go Fujita & Bell 1973; Merton 1973, 1975; Bell 1978). and Hisashi Nagata Despite the increasingly common application of
89 J. P. PIERRE translocations in conservation management, and wide shore islands, it is unable to coexist with introduced recognition of the value of post-release monitoring predators, and consequently, was virtually extinct by (e.g. Scott & Carpenter 1987; Griffith et al. 1989; 1900 (Oliver 1955; Roberts 1991). The total popula- Sarrazin & Barbault 1996), such monitoring does not tion of South Island Saddlebacks is currently about always occur. In fact, Wolf et al. (1996) reported that 650, with birds occurring on 11 islands, all of which only 45% of 336 bird and mammal translocation pro- are free of introduced predators. grams included tagging of released individuals or Following the South Island Saddleback Recovery post-release telemetry, and in about 30% of transloca- Plan (Roberts 1991) administered by the New tions, the causes of 90–100% of animal losses were Zealand Department of Conservation, 26 South Is- never identified. In New Zealand, translocation con- land Saddlebacks were translocated to Motuara Is- tinues to be widely used as a conservation tool. Post- land in the Marlborough Sounds from the Titi Islands release monitoring of translocated animals may be near Stewart Island, New Zealand, in March 1994. becoming more common (e.g. Nelson et al. 2002), (See Figure 1 for the locations of islands mentioned but such monitoring seldom occurred in the past (De- in the text). Seven adult males, 11 adult females, 5 partment of Conservation 1994; Lovegrove & Veitch subadult males, one subadult female and one adult 1994; Armstrong & McLean 1995). and subadult of unknown sex were included in the Similar to post-release monitoring of survival, translocated founder population. Motuara Island (59 monitoring the habitat use of newly translocated or- ha) was selected as the release site for translocated ganisms is important, yet seldom occurs. Globally, South Island Saddlebacks for three main reasons. translocations are deemed most likely to succeed First, introduced predators (Rattus exulans) were ex- where animals are released into areas of high habitat tirpated from the island in 1993. Second, vegetation quality and/or quantity (Wolf et al. 1996). This em- on Motuara Island has been regenerating since farm- phasizes the importance of thoroughly investigating ing was abandoned in 1926 (W.F. Cash pers. comm.), the habitats at potential release sites before conduct- and finally, the bird was historically resident in the ing translocations and monitoring the habitat use of area. Conservation managers considered Motuara Is- translocated animals after they are released. Post-re- land to be sufficiently large and with appropriate lease monitoring of habitat use can confirm suitability of the new location, and produce valuable informa- tion relevant to future translocations, thereby facili- tating adaptive wildlife management (Sarrazin & Barbault 1996). For example, mobile animals at low densities may occupy habitats on the basis of prefer- ence rather than requirement, and may colonise less ‘preferred’ areas as their population density increases (Jenkins 1976; Armstrong & McLean 1995). There- fore, monitoring spatiotemporal patterns of habitat use together with population growth can be informa- tive in determining habitat requirements and prefer- ences, and the ability of translocated organisms to colonise ‘novel’ environments. The South Island Saddleback is a forest passerine endemic to the islands of New Zealand. It is an en- dangered subspecies of the near threatened New Zealand Saddleback (IUCN 2000). Diurnal, territorial and largely insectivorous, the South Island Saddle- back forages on foliage, live and dead wood, and the ground. It uses cavities for roosting and is monoga- mous with apparently flexible nest site requirements (Guthrie-Smith 1925; Pierre 1995). Although the South Island Saddleback was formerly widespread Fig. 1. Locations of islands mentioned in the text. (From over New Zealand’s South Island and southern off- Pierre 1999).
90 South Island Saddleback reintroduction habitat to support more South Island Saddlebacks data using paired t tests and analysis of variance than currently existed on any other island (W.F. Cash (ANOVA) conducted in SPSS 8.0 (SPSS Inc. 1997). I pers. comm.). used Games-Howell post-hoc tests (Day & Quinn In this paper, I review the reintroduction biology of 1989) to identify homogeneous subgroups after sig- the South Island Saddleback. I discuss post-release nificant ANOVAs, and Bonferroni a adjustments dispersal, social organisation, survival, habitat use when appropriate, including in G tests described and foraging patterns of the newly released popula- below (Miller 1981). See Pierre (2001) for a discus- tion on Motuara Island, New Zealand. Before the sion of how pseudoreplication and problems of inde- work described in this review was carried out, the pendence were minimized. South Island Saddleback had not been studied in de- I characterised vegetation using a transect-quadrat tail. Also, future translocations were planned to in- sampling method, and sampled both saddleback terri- crease the total population of this bird (Roberts tories and one area uninhabited by saddlebacks 1991). For these reasons, post-release monitoring of (Pierre 2001). I defined plant availability as the cross- the translocated population was critical. sectional area of each plant species at breast height, and the availability of dead wood as the proportion of METHODS total quadrat area it covered on each transect (Pierre 2001). Vegetation characteristics were compared be- Saddlebacks were weighed, measured and their tween sites using G tests (Zar 1996). plumage examined on capture to determine sex and age (W.F. Cash pers. comm.; Nillson 1978; Jenkins & RESULTS Veitch 1991). Numbered metal and unique combina- tions of coloured plastic legbands were used to iden- After release, South Island Saddlebacks ranged tify individuals. After release on Motuara Island, widely through the forested areas of Motuara Island. birds were relocated using a recording of South Is- By the start of the first post-release breeding season, land Saddleback male territorial song, and via their both adult and subadult birds appeared to have settled vocal responses and attraction to disturbances (e.g. on territories, which varied in size from 1.9–8.8 ha logs breaking). The work reviewed here results from (X¯ 4.21 ha, SD 2.42, N 6, Figure 2, Pierre 1999). post-release monitoring involving intensively search- Adult and subadult saddlebacks announced their ing for birds for four days, six months after they were presence vocally from a range of vertical locations in released, and searching for and monitoring birds for their territories, especially in the first two hours after 56 days, from eight months after release, during their dawn, and for approximately one hour just before first breeding season on Motuara Island. dusk. However, confrontations between neighbours Territory boundaries were identified during the appeared very rare, and I observed only one during breeding season by conducting repeated searches for the study. This low frequency was despite saddle- birds and recording the locations of song posts. I backs venturing into each other’s territories, which I monitored birds for 90 minutes during these tracking observed on five occasions during my research, and episodes; tracking beyond five 90 minute sessions did which at least sometimes appeared related to searches not alter the perceived location of territory bound- for water (Pierre 1999). aries (Pierre 1999). As well as recording song posts, I The vegetation composition of saddleback territo- monitored habitat use by birds, including substrates ries on Motuara Island differed significantly, and was used for foraging and other activities, and heights of different again in areas uninhabited by saddlebacks the forest that birds occupied (Pierre 2001). I also (G tests, vegetation composition in all territories recorded prey identity when possible, and where prey compared to all other territories and a vegetated area were caught (Pierre 2000). Saddleback nests were lo- not occupied by saddlebacks: G8 2117.36, P 0.005, cated by following birds holding nesting materials, Pierre 2001). However, all territories were in forest and by checking nest boxes. To avoid disturbing nest- areas and included plants of similar size distributions ing birds, I did not check nests frequently after locat- (G tests: plant sizes in all territories compared to all ing them. Instead, I monitored breeding activities in- other territories, G5 14, P 0.005, NS). In contrast, directly by assessing the behaviour of adult birds saddlebacks did not inhabit a locality covered by (Pierre 1999). smaller diameter plants, in this case scrub (G tests: all I conducted analyses of habitat use and foraging territories compared to an area uninhabited by saddle-
91 J. P. PIERRE