BRANTA — Friederike Woog
Ecology and behavior of reintroduced Hawaiian Geese
Institution: University of Hannover, Germany & Wildfowl & Wetlands Trust, UK
Supervisors: E Zimmerman, JM Black (WWT)
Details: PhD 1999 (Completed)
Current Address: Staatliches Museum für Naturkunde Stuttgart, Rosenstein 1, 70191 Stuttgart, Germany (Dec 2006) Email
Subject Keywords: conservation, breeding, dispersal, flock structure, grassland management
Species Keywords: Hawaiian Goose (Nene) Branta sandvicensis
Abstract
This study investigates the ecology and behavior of Hawaiian Geese (Branta sandvicensis) in relation to reintroduction into the wild.
After release, Hawaiian Geese established breeding populations around rearing and release pens, but after the maintenance of lowland pens was discontinued, birds moved away and colonized new breeding habitats. New breeding habitats were mainly located at mid-altitude volcanic scrublands with little vegetation cover. Wild-bred goslings and goslings reared by free-flying parents inside predator proof pens paired and bred earliest. Parental contact was apparently important not only during rearing but after release, suggesting that young should be released with their parents.
The distribution of individual Hawaiian Geese varied between years. Some birds were faithful to a restricted number of areas but others ranged more widely. Individual movement was similar between years and seasons. There was no consistent monthly movement pattern. Single birds and pairs moved in similar proportions.
The phenology of food plants varied between sites, rainfall and with elevation and affected the seasonal distribution of individually marked Hawaiian Geese. Geese appeared to time their movements and nesting according to local food availability. Generally, geese that nested earlier in the season, when berry availability was high, tended to be more successful in rearing young but external events, such as predation, caused some early breeders to fail.
Two overgrown grasslands were mowed and compared with established grasslands that had previously been mowed or grazed by livestock. Sites differed in plant species composition and quality, seedhead production, grass height and rainfall. Hawaiian Geese grazed more in sites that had plants of high nutritional quality. Over time, the variation in rainfall explained a large part of the differing grazing pressure, suggesting that geese used grasslands less during dry periods. Hawaiian Geese remained in established sites and did not move to newly managed sites. To encourage feeding opportunities, my results suggest that grasslands could be managed at a height below twelve centimeters, irrigated in drought periods and fertilized.
Since 1960, 366 goslings are known to have fledged in the three release regions, including 196 in the wild and 161 in or around pens. Maybe due to higher rainfall and better foraging conditions, clutch size at Haleakala was greater than on Hawaii. Birds in pens reproduced better than those in the wild, reflecting reduced predation and enhanced feeding opportunities. When paired to a wild bird, released birds were more successful than when paired to a released bird. Parent-reared birds in large open top pens, which eventually flew from the pens after fledging, reproduced most successfully. Most birds nested in open scrubland where they were more successful than in grassy scrub.
In captivity, clutch size and the number of eggs hatched initially increased with age in males and females, then levelled off and declined for older birds. The number of eggs hatched initially increased with pair duration, but decreased later. Body size did not affect reproductive success.
Hawaiian Geese were compatible with their partners to a varying degree. The behavioral fine-tuning of partners in social displays varied in relation to the relative age, size and pair duration of partners as well as to the distance with which partners associated. Females that showed stoic responses to overt male behavior had a lower hatching success. In contrast, when the male displayed less intensely in relation to the female, pairs were more likely to have a clutch.
Published Papers
Woog, F., & Black, J.M. 2001. Foraging behavior and temporal use of grasslands by Nene: implications for management. Studies in Avian Biology 22: 319-328.
Woog, F. 2002. Distribution and timing of nesting in Hawaiian Geese in relation to food phenology in scrublands.Wildfowl 53: 78-106.
Woog, F. 2002): Reproductive success and pairing in Hawaiian Geese (Branta sandvicensis) in relation to age and body size. Journal für Ornithologie 143: 43-50.