Current and recent research

Mudflats in this region are of particuar important to Semipalmated Sandpipers, which use the area as a staging ground on their fall migration from the Arctic to South America. Each year in late summer, hundreds of thousands sandpipers visit the upper Bay of Fundy. While here, they feed extensively, roughly doubling their mass during a stay of approximately 3 weeks. C. volutator has historically been thought to be their most common prey, though other species are taken. In recent years, we have observed substantial fluctuation in C. volutator populations. This leads to concern about stability of the community and availability of food for migrating shorebirds.

I have been working on various ecological questions associated with these mudflat communities since 1999. Most of the focus has been on interactions between shorebirds and the community, though recently we have focused on tracking shorebird movements and habitat use. Following are some of the main recent and ongoing projects occurring in my lab:

Effects of shorebird predation on C. volutator and the rest of the mudflat community - Using predator exclosures and fertilizer application, we examine top-down and bottom-up forces on mudflats, including direct and indirect effects of shorebirds during their stay in the region. We have found that shorebird predation does indeed reduce abundance of C. volutator, but that it is not responsible for all losses (Hamilton et al. 2006). We have also found that shorebirds affect vertical distribution of adult C. volutator by causing them to move deeper into the sediment (MacDonald et al. 2014), and that effects of shorebirds may be mitigated or exacerbated by presence of mudsnails, which also negatively affect C. volutator (Hamilton et al. 2006, Cheverie et al. 2014).

Duration of stay, movement and habitat selection by Semipalmated Sandpipers - Working in collaboration with Environment Canada (Julie Paquet, Cheri Gratto-Trevor), we recently completed two detailed studies of sandpiper movements within and adjacent to the upper Bay of Fundy. We have also radiotracked birds tagged on the Acadian Peninsula, in the Arctic, and in James Bay during their time in our region. All tracking is done as part of the Motus Wildlife Tracking System, which offers us the opportunity to follow movements of our birds over a wide area. We are also examining habitat use relative to food availability, and looking at sex-related differences. Results suggest that birds remain in the region considerably longer than previously thought. We have also identified regional staging populations that exhibit little mixing during the time in the area, though extensive movement within their regions. Work by M.Sc. graduate Sarah Neima has confirmed that birds segregate between arms of the Bay of Fundy within years, and based on a resighting study we have also learned that individuals return to the same arm of the Bay in subsequent years (Neima et al. 2020). Sarah also identified key departure points, and found that departure timing is linked to specific weather patterns. Duration of stay is therefore influenced by far more than just time needed to refuel. Honours student Hilary Mann studied movements and duration of stay in Cobequid Bay, Nova Scotia. She found that birds exposed to extremely high tides that resulted in limited roost sites engaged in over ocean flocking rather than going elsewhere to roost (Mann et al. 2017). This appears to have led to increased energy costs, and longer stay times in the region. From 2018 to 2020 we conducted a follow up study of Semipalmated Sandpipers in this region, examining juveniles and adults using habitat both inside and outside the Bay of Fundy. This was part of Siena Davis' honours thesis and Rebeca Linhart's M.Sc. thesis. Rebeca found that some birds tagged outside the Bay of Fundy remained outside the Bay, whereas others transferred to the Bay and remained there. Duration of stay is longer for Bay of Fundy birds than coastal birds.

Diet and foraging behaviour of Semipalmated Sandpipers - It has been traditionally assumed that C. volutator is a critical food source for migrating sandpipers, and indeed most sandpipers are found where C. volutator is most abundant (Hamilton et al. 2003, Ashley Sprague M.Sc. thesis, 2006). However, sandpipers have been observed at one site exhibiting a novel foraging behaviour which is similar to related species that consume biofilm, suggesting that they may be exploiting this alternate resource. M.Sc. student Matthew Ginn used a combination of stable isotope analysis of blood plasma and behavioural observations linked to food availability to address these questions. He found that biofilm was indeed a significant part of the diet of sandpipers in one year, but unimportant the following year. However, the consumption of biofilm appears to be incidental, in that there was a strong link between the observed "skimming" behaviour and ostracods, another novel prey item, but not linked to biofilm abundance (MacDonald et al. 2012). These results highlight the flexibility of sandpiper diets in situations where C. volutator is in low abundance. M.Sc. student Jenna Quinn has expanded this work to examine birds from more areas, and looked at fatty acid profiles of the various prey appearing in the diet. Her work has revealed diet differences in different areas of the Bay of Fundy (Quinn and Hamilton 2012). She has also noted that polychaetes have similar fatty acid profiles to Corophium, and that biofilm may be a profitable food item if consumed in sufficiently large quantities (Quinn et al. 2017). Ph.D. student Travis Gerwing developed a molecular technique to allow us to identify prey consumed in feces collected from the mudflat (Gerwing et al. 2016). He found that Semipalmated Sandpipers have an extremely broad diet consisting of inputs from marine, freshwater and terrestrial sources.

Importance of mudsnails in mudflat communities - Mudsnails (Ilyanassa obsoleta) are important in intertidal mudflat communities. They have substantial negative effects on C. volutator, which may be the result of interference and/or exploitation competition, leading to increased patchiness, reduced populations and limited movement into areas of high snail density (Drolet et al. 2009). We also have evidence that they directly feed on C. volutator under lab conditions (Coffin et al. 2012). In recent years we have determined that mudsnails can compensate for both bottom-up and top-down forces, effectively blocking a trophic cascade (Hamilton et al. 2006), that their presence is a strong predictor of sandpiper habitat use (Hamilton et al. 2003), and that they display a strong preference for tide pools (Coffin et al. 2008), which are also preferred habitat for C. volutator. M.Sc. student Mike Coffin is has conducted lab and field experiments to further understand interactions between these two species. Honours student Miriam Coulthard examined the effect that snails may have on the vertical distribution of C. volutator in the mud, which in turn will affect prey availability for shorebirds (Coulthard and Hamilton 2011).

Mudflat community composition - Former Ph.D. student Travis Gerwing undertook a large scale observational study in which he collected data on biotic and abiotic aspects of mudflat ecosystems throughout the Bay of Fundy. He concluded that most biotic and abiotic factors appear to be only weakly associated with community structure (Gerwing et al. 2015, 2016), and suggested that community strucure may be driven by "first come first served" community dynamics. Recent M.Sc. graduate Greg Norris undertook a manipulative experiment where we test that hypothesis. Large plots on mudflats were rendered azoic, and we are followed community recovery. Greg found that there was no evidence of preemptive competition, and that the community composition gradually approach control plots. Community structure largely depended on what was in the regional species pool, and these results were independent of season and moon phase.

Shorebirds outside the Bay of Fundy

I have recently completed a collaboration with Julie Paquet, Canadian Wildlife Service, and Fletcher Smith and Bryan Watts, Center For Conservation Biology, College of William and Mary, Virginia. We examined ecology of Whimbrel using the Acadian Peninsula of New Brunswick as a stopover point during their annual fall migration. These birds have come into conflict with commercial blueberry growers because the berries provide a rich food supply and attract Whimbrel to the fields. In 2015 honours student Avery Nagy-MacArthur examined activities of Whimbrel in berry fields. We also attempted to capture and track birds using avian nanotags and the Motus Wildlife Tracking system. We continued that work in 2016 in an effort to quantify the extent to which Whimbrel use berry fields, as well as their general movements and duration of stay in the area. We deployed a small number of satellite tags that will facilitate worldwide tracking, allowing us to gain insights into migratory connectivity (Watts et al. 2019). In 2017, honours student Jessie McIntyre undertook a GIS-based project to examine habitat characteristics, including temporal changes, to the landscape used by Whimbrels on the Acadian Peninsula. She has also undertaken an important outreach project, collaborating with Dr. Julie Guillemot, Université de Moncton, to help inform blueberry growers about the importance of these areas to Whimbrels.

We also captured and radiotracked several other shorebird species on the Acadian Peninsula in summer 2016, and in summer 2017 focused on Semipalmated Plovers and Semipalmated Sandpipers. This has helped us to understand important habitat in the area, as well as understand whether birds staging in the area also use other parts of Maritime Canada during their fall migration. Honours student Erica Geldart worked with radiotracking data and habitat data obtained during these two years. We are also examining fattening rates of birds relative to prey consumption and foraging behaviour. Honours student Hannah MacKellar studied plasma triglyceride levels in these two species, and related findings to diet, behaviour, and length of stay in the region. Continuing from this work, honours student Jana Arseneault completed a tracking study on White-rumped Sandpipers, and in 2020 honours student Parker Doiron examined local movements of multiple shorebird species that frequent habitat on the Nothumberland Strait. He found that most birds used relatively restricted ranges, and that juvenile birds moved around more than adults, suggesting they may use a wider range of habitat. M.Sc. student Allie Hjort is continuing this work, and looking at both local and regional movements of a range of late migrating species.

Honours students Sara Bellefontaine and Veronica Ouellette examined foraging ecology and niche partitioning among the shorebird community at a site on the Northumberland Strait. Sara found that species partitioned resources based on diet and habitat use. Veronica found that shorebirds used the habitat during day and night, and that at night the Calidrid species switched to skimming behaviour, whereas the plovers simple ceased foraging.

In winter 2019 we also substantially expanded our research area, initiating a student on wintering Semipalmated Sandpipers in Brazil. We are collaborating with Julie Paquet, CWS, and Aquasis - a conservation NGO in North Eastern Brazil. We erected Motus tracking towers near our study sites, tagged birds, and collected both blood samples and behaviour observations. Rebeca Linhart spent two winters in Brazil and identified intriguing movement patterns and evidence of multiple habitat use strategies. We anticipate that this will be a long term collaboration.

Rocky Intertidal Ecology

During my Ph.D., I examined interactions between diving ducks (primarily Common Eiders) and the rocky intertidal community in which they feed. I found that ducks had a substantial effect on mussel beds, that abiotic disturbance altered this relationship, and that dogwhelks (Nucella lapillus) compensated for absence of ducks, preventing a top-down trophic cascade in the system (Hamilton 2000). Duck predation was much less important in an adjacent rockweed (Ascophyllum nodosum) bed, where dogwhelks appeared to be more important (Hamilton and Nudds 2003). Several year ago we completed a series of studies that followed up on some of these findings. M.Sc. student Melanie R. Boudreau examined direct and indirect interactions between ducks and a number of invertebrate predators of blue mussels. Using exclosures and enclosures, she manipulate separately and together densities of predators, and examined the resulting community structure in Passamaquoddy Bay, New Brunswick. She also examined the effect of experimental timing on results, and found that the ability of other predators to compensate for duck exclusion varies depending on the state of the mussel bed at initiation of the experiments (Boudreau and Hamilton 2012). Honours student Brady Quinn examined predation rates of dogwhelks and green crabs held in field enclosures in varying densities and combinations (Quinn et al. 2012). Honours student Melanie L. Boudreau conducted similar trials under lab conditions and with varying predators sizes (Boudreau et al. 2013).