Assessing the impact of lesser snow goose and cackling goose competition on breeding Atlantic brant
| Author(s) | Nissley, Clark | |
| Date Accessioned | 2017-06-07T11:25:45Z | |
| Date Available | 2017-06-07T11:25:45Z | |
| Publication Date | 2016 | |
| Abstract | Population estimates from Mid-Winter Survey Counts over the last half century show that Atlantic brant numbers have fluctuated over the course of this time period; however, between 2000 – 2016 the population has been showing a slow decline of ~20%. Additionally, the Mid-Winter Surveys (MWS) indicate a low percentage of young in flocks in recent years (<10% between 2013–2015), indicating breeding ground limitations in those years. Southampton Island’s East Bay (located on the southern end of the Foxe Basin), supported a historic nesting colony of brant as well as a significant population of lesser snow geese (Chen caerulescens caerulescens) and a small population of cackling geese (Branta hutchinsii). However, range-wide, lesser snow geese populations have increased from a few million to ~15 million in the last few decades with consequences that resonate throughout the ecosystem, affecting other species sharing that ecosystem. Additionally, the MWS indicates the range-wide cackling goose population has also increased from ~400,000 to ~700,000 in the last 3 decades. ☐ While East Bay historically supported a large nesting colony of Atlantic brant. Research crews in 2010 found that a local decline in brant nesting had occurred, though reasons for the decline were not resolved. The aim of my study was to begin to decipher the keys to understanding why a localized decline is occurring and to provide an update of the status of nesting Atlantic brant at East Bay. By means of nest searching, the careful observation of brant pairs during incubation, and collection of habitat and nest site selection data, we now believe we have a better grasp on some of the factors limiting brant success at East Bay, Southampton Island. ☐ Snow geese and cackling geese arrived 25 May 2014 and 21– 22 (respectively) May 2015. Brant arrived on 9 June in summer 2014 and 8 June in summer 2015. Snow melt in 2014 occurred much faster than snow melt in 2015. In 2014, snow cover reached 0% by 12 June, while in 2015 snow cover did not reach 0% until 28 June. The snow melt was much quicker in 2014, with 100% snow melt lasting only until ~23 May as compared to 2 June in 2015. The peak initiation for snow geese was 2 June in 2014, but 14 June in 2015. Following a similar pattern, the peak initiation for cackling geese was 6 June 2014 and 19 June 2015. Brant had a less pronounced difference between years, peaking on 18 June 2014 and 22 June 2015. Importantly, the late snow melt in 2015 also caused a significant reduction in initiated nests in cackling geese (from 570 in 2014 to 355 in 2015) and snow geese (from 230 in 2014 to 48 in 2015) and an increase in brant nests (from 44 in 2014 to 78 in 2015). Atlantic brant and lesser snow geese did not overlap in their nesting habitat in 1979, nor did they between 2010–2015 when their nesting habitat appeared to be segregated between the upland (snow geese) and the graminoid/moss zones (brant). By 2010–2015, cackling geese populations at East Bay increased and appeared to wedge between Atlantic brant and lesser snow geese populations, thus overlapping with brant nesting regions. In 1979, 88.5% of Atlantic brant had at least 2 other brant nests within 200 m of their nest. By 2010 that decreased to 18.4% and further declined to 13.6% in the 2014 breeding season, but rebounded slightly to 26.9% in the 2015 breeding season. In contrast, in 1979 only 5% of Atlantic brant had at least 2 or more cackling goose nests within 200 m of their nest. That increased to 46.1% by 2010 and to 40.9% in 2014. In 2015, due to the lower number of cackling goose nests, only 16.7% of brant nests included 2 or more cackling goose nests within 200 m. Even though there were a lower number of nesting cackling geese in 2015, I still found 39% of 2014 brant nest sites were occupied by a cackling goose nest (< 200 m) showing the strong overlap in preferred habitat. ☐ Kruskal-Wallis tests revealed significant differences between male and female brant behaviors between 2014 and 2015. Male brant spent less time feeding as well as less time engaged in locomotive behaviors (swimming/walking) in 2014 than in 2015. Females on the nest spent more time alert more time engaged in nest construction behavior in 2014 than in 2015. Females off the nest spent less time feeding and less time flying in 2014 than in 2015, but more time alert and more time preening. ☐ Mean island size, mean water depth, and mean water distance did not differ between cackling geese and Atlantic brant in summer 2015 when these data were collected for both species indicating brant and cackling geese prefer similar island nest sites. Water distance was defined as the distance from a nesting island to the nearest mainland body. This path was chosen by finding the shallowest water path, with the assumption that a fox will use the shallowest path to access an island. If islands were scattered across that path, then the water distance between those islands was measured and summed (i.e. distance to island #1, distance to island #2, etc.). Brant apparent nest success declined from a high of 86% in 1979 to 65% in 2010, 5% in 2014, and 17% in 2015. Cackling goose nest success dropped from 86% in 2010 to 61% in 2014 and to 2% in 2015. Snow goose nest success was lower (63%) in 2010 compared with 74% in 2014; but then dropped to 6% in 2015. The overwhelming majority of failures were due to arctic fox depredation, responsible for 82% of brant failures in 2014 and 73.3% of brant failures in 2015. I examined the impact of nest site selection on fox predation. The top model included year, maximum water depth, distance to a mainland (water distance), and whether or not the nest was located on an island. Both year and maximum depth had the greatest effect size within the top model. Brant daily nest survival was 0.828 (SE + 0.029) in 2014 and 0.924 (SE + 0.012) in 2015. ☐ I conducted an artificial nest experiment and calculated Kaplan-Meier survival probabilities for artificial nests located in different density plots (high vs. low goose nest density) and found high density nesting plots to experience increased predation and decreased survival probability. ☐ Preliminary evidence at East Bay reveals a complex system in which many factors are influencing the localized decline of brant nest success and local population. My results indicate that at least some level of four kinds of competition (exploitative, preemptive, interference, and apparent competition) is occurring at East Bay. Whether or not these forms of interspecific competition have larger implications for the brant population as a whole remains to be studied at other breeding locations. I also found weather to have a profound impact on the nesting success of geese and the level of competition displayed between different goose species at East Bay.The role that climate change may play in brant survival and reproduction in future decades is yet to be seen, but I believe the importance of weather and climatic variables in the success of East Bay brant indicates that it will play a large role in the future of all breeding brant colonies. | en_US |
| Advisor | Williams, Christopher K. | |
| Degree | M.S. | |
| Department | University of Delaware, Department of Entomology and Wildlife Ecology | |
| Unique Identifier | 989119262 | |
| URL | http://udspace.udel.edu/handle/19716/21431 | |
| Publisher | University of Delaware | en_US |
| URI | https://search.proquest.com/docview/1853453060?accountid=10457 | |
| dc.subject.lcsh | Brant -- Nunavut -- Southampton Island. | |
| dc.subject.lcsh | Snow goose -- Nunavut -- Southampton Island. | |
| dc.subject.lcsh | Cackling goose -- Nunavut -- Southampton Island. | |
| dc.subject.lcsh | Bird populations -- Nunavut -- Southampton Island. | |
| Title | Assessing the impact of lesser snow goose and cackling goose competition on breeding Atlantic brant | en_US |
| Type | Thesis | en_US |