The Changing Face of Predation on Arctic Nesting Birds presented by Ken Abraham, Ministry of Natural Resources
Cool summer in the Arctic is ‘nice’ for the many ground-nesting birds that make the trip
Lecture report by Lynda Bennett
Dr. Ken Abraham, wetland and waterfowl scientist with the Wildlife Research Team of the Ministry of Natural Resources recently spoke at a Mississippi Valley Field Naturalists (MVFN) meeting in Almonte. His talk “The Changing face of Predation on Arctic Nesting birds” focused on climate change and several remarkable ground-nesting birds of the Arctic, including Red Knots, Semipalmated Plovers, Snow Geese, Eiders and Whimbrels. Some of these birds make spectacular migrations to get to the Arctic only to nest and raise young in a relatively harsh landscape. The Red Knot, a small shorebird, is a good example. In a few days it flies from the Southern tip of South America to the northern tip of Canada. Tracking by satellite shows migration is on a very fixed route and feeding stops are essential. In Delaware Bay, on the Atlantic coast, they have a feeding frenzy on the eggs of Horseshoe Crabs amassing onshore, potentially doubling their weight in a few days! This resource is absolutely critical for migration. Another long-distance migrant, the Whimbrel, deals with hurricanes on its way from Brazil!
Why do these birds make the long journey to the Arctic? Relief from predation is part of the answer. In a simple demonstration experiment Abrahams and colleagues placed nests along a line north from James Bay to the Arctic Ocean. The nests were subject to less predation (primarily from foxes) the farther north they were; it was 3.6% less per degree of latitude northward. In this case predation appears to act as a ‘top down control’ of the nesting population. Factors shaping populations can be approached from a ‘top-down’ or ‘bottom up’ view. ‘Top down’ factors include predation, weather and disease as major factors in nest success. ‘Bottom-up’ factors include resources such as food abundance, nest sites and water availability.
Although it is clear ground nesting birds do get some relief from predators in the Arctic, they are still preyed upon by many species including Arctic Foxes, other birds such as gulls, eagles and Parasitic Jaegers, and, as it turns out, to an increasing degree by Polar bears. There are complex predator-prey relationships at work in the Arctic. A common theme of the interplay of these arctic ground nesting birds and the animals who prey on them is the effects of the relative abundance (and its cyclical or geographical variation) of the preferred prey of the predators. For example Dr. Abrahams explained that although the Arctic Fox is a major predator of many arctic ground-nesting birds, Lemmings are actually its ‘preferred’ prey, and Snow Geese are only the ‘alternate’ prey in low Lemming years. Still other Arctic birds may only be ‘incidental’ prey for the Arctic Fox, when neither Lemmings nor Snow Geese are present in the area.
Our speaker used interesting examples and illustrations to show how Arctic ground nesting birds use the Arctic habitat to their advantage and have evolved several strategies to ensure their nests are as successful as possible. Semipalmated Plovers, for example are: i) masters of camouflage, using the sparse landscape to hide their beige/grey spotted eggs ‘in plain sight’ on open pebbly ground, ii) masters of distraction displays, faking an ‘injured wing’ to lure prey away from vulnerable eggs or chicks, and iii) use nest associations to conceal themselves, i.e. evidence shows they benefit from nesting in close proximity to Arctic Terns whose aggressive defensive behavior discourages predators.
Ken Abrahams (standing left) is thanked by MVFN Vice President Stephen Collie. Abrahams spoke about Arctic breeding birds to a large audience. Ground-nesting birds do get some relief from predators in the Arctic, but they are still preyed upon by species such as Arctic Fox, birds including gulls, eagles and Parasitic Jaegers, and, as it turns out, to an increasing degree, Polar Bears! Photo Pauline Donaldson
Species such as Whimbrels nest on the ground near dwarf shrubs, or hummocks using lichen and other things. to disguise their nests. Early nesting, short incubation and precocious chicks are other strategies to avoid predators, e.g. Red Knot hatching is synchronized and hatchlings begin foraging with parents within a day.
Another strategy involving safety in numbers is the colonial nesting of the common Eider. There are more nesting Eiders in the high Arctic than in the lower and as Abrahams explained they are adapted to nesting in tight, large crèches with multiple hatchings on islands with usually few or no predators. They are tame and not used to predators, so have little defense against increasing predation by, for example, Grizzly Bears moving northwards with climate change. Even Bald Eagles, having made a come-back since the banning of DDT, can do quite a lot of damage to nesting Eiders.
Abrahams concluded with further insights into how climate change is changing the ‘face’ of predation in the north. Polar Bears were seen eating numerous Snow Geese eggs; they are coming to land earlier and earlier each year due to ice melting. On land they cannot access their preferred traditional prey, seals. New camera technology is helping Abrahams and other researchers get a better idea of what is going on. A camera set up opposite a Snow Goose nest revealed that even Black Bears are finding their way up to the low Arctic now and were seen destroying large numbers of Snow Geese eggs; and Barren Ground Caribou trample on a good number of nests