Posted on 6/6/2012 by Mitch Weegman
After a period of increase, the global Greenland White-fronted Goose population has declined markedly since the late 1990s due to low reproductive success in recent years. In 2006, hunting of white-fronts was banned in Iceland, yielding complete protection throughout their annual cycle. This conservation strategy has halted the decline, but the cause of low breeding success continues to puzzle researchers.
Greenland White-fronted Geese breed in west Greenland, stage during autumn and spring in Iceland, and winter in Ireland and western parts of the United Kingdom. The purpose of my Ph.D. research—a collaboration between the University of Exeter and Wildfowl and Wetlands Trust—is to understand the reasons for the population decline and low rates of reproductive success.
One approach to improve our biological knowledge of these birds is to examine decisions made by individuals throughout their life cycle and ultimately link these to reproductive output in successive years. Greenland White-fronts are unique among waterfowl in that less than 5% of individuals marked in their first winter of life ever breed. It is this enigmatic portion of the population that I will study. In addition, we hope to gain insight about the other 95% of the birds that never breed, but migrate to Greenland each spring. Fortunately, collaborators in Ireland and Britain have maintained, since 1982, a long-term database of resightings of marked individuals and counts of all known regular wintering habitats. Thus, there is a wealth of historical data to analyse.
Flock sizes have fluctuated at most wintering habitats since counts began, although the mechanism for this dynamic is not understood. However, the large flock at Wexford, Ireland—that numbers over 8,000 birds—has remained relatively stable since the early 1990s, despite overall declining population size. This decline is in contrast to the flock at Islay, an island off the western coast of Scotland, where numbers more than doubled to 15,000 birds, but now have declined to levels similar to the late 1980s. By analysing these data, I hope to help explain variation in flock sizes and specific strategies of breeding birds.
To examine behavior of individuals and how this affects their propensity to breed, I began fieldwork in Ireland and Scotland during winter 2011-2012. I attached GPS/accelerometer tags to 20 male Greenland White-fronts. I chose to mark males instead of females to avoid any potential reproductive bias and because males are typically larger than females, minimizing tag weight effects. The tags record one GPS fix per day and an electronic trace of movement in three dimensions that enables us to record behavior every six minutes over an annual cycle. Data may be downloaded remotely to a base station less than a mile away. This fine-scale behavioral data will provide new insights into strategies of individual birds.
Another important aspect of my work was observation of social interactions between family groups. We believe larger family groups enjoy access to quality food and habitat throughout the year, therefore potentially contributing the greatest number of young annually to the population. Over the next few years, I would like to compare biological outcomes (e.g., body condition, survival, etc.) of these white-fronts and conspecifics without membership in large family groups to understand possible differences in life-history strategies.
While family group size may be very important to breeding success, overall body condition of birds and food availability during migration are issues ornithologists have pinpointed for many years as fundamentally important for population dynamics. Beginning in the early 1980s, studies of staging Greenland White-fronted Geese have taken place at Hvanneyri, Iceland, home of the Agricultural University of Iceland and one of the most important known staging areas for Greenland White-fronts as they migrate to Greenland.
To determine overall condition of birds, we brought a 12-member team consisting of professionals and volunteers from the Czech Republic, Denmark, England, Ireland, and Scotland. We conducted daily goose counts, documented the amount of fat storage by scoring abdominal profiles of individuals, and resighted collared birds from 3 April to 6 May 2012. An average of 1,000 Greenland White-fronts were counted on fields of the Agricultural University; peak numbers occurred 22 April, when nearly 2,000 were counted. In addition, the team generated over 900 resightings of collared birds; most were collared at Wexford, Ireland. A few resightings were of birds collared in the late 1990s, making them 12-15 years old. Two of the team members, Kerry Mackie (Wildfowl and Wetlands Trust) and Alyn Walsh (National Parks and Wildlife Service of Ireland), coordinated rocket-netting efforts, catching 69 new birds this year. These newly collared birds in the population will contribute to our studies and the estimates of long-term survival of individuals.
Preliminary results from this spring suggest birds arrived 10-14 days earlier than average, as conditions in Iceland were mild and snow had melted by mid-February. In fact, first flocks arrived 24 March, the earliest documented arrival date. Further, white-fronts were in exceptional condition from early April. Abdominal profiles of many individuals during early April were similar to those of birds departing for Greenland in years past. We also observed many birds resting and not foraging in fields throughout the day, perhaps due to their exceptional condition. However, despite excellent condition of geese by mid-April, average departure date only was six days earlier than in previous years. These results suggest the staging period in Iceland is actually increasing in duration. Historically, white-fronts have staged for three weeks, but this period has now increased to nearly six weeks. Although further research is needed on staging areas, it seems likely changes in climate have resulted in warmer conditions and thus increased forage opportunities in Iceland, which the birds are exploiting.
The trip to Iceland completes the fieldwork for this season. We’ll return with the geese to wintering sites in Ireland and Scotland in November, as we continue to follow the 20 tagged birds. Ideally, we’ll use historical and tag data to better understand the Greenland White-fronted Goose population decline and provide management recommendations to return this important population to favorable conservation status. I look forward to seeing my U.S. colleagues and friends in Memphis, TN in January at the symposium, Ecology and Conservation of North American Waterfowl, where I’ll provide further results of my research.