2012-2013: Nature Beneath Our Feet
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
Survivor: Winter Wildlife—Outwit, Outlast, Outplay presented by Patty Summers, Wild Bird Care Centre
Survivor: winter wildlife edition
Lecture report by Elizabeth Wiles & Pauline Donaldson
A delightful, clearly delivered talk to the Mississippi Valley Field Naturalists by Patty Summers from the Wild Bird Centre, February 2013 described the varied and intriguing ways wildlife will prepare to survive winter. How will they do it? Summers divides wildlife winter-survivor strategies into three categories – outwit, outlast and outplay, with outwit being by far the most widely employed strategy.
Outwitting winter, Summers explained, involves turning the tables, knowing the science of cold and of snow and cold water to find the secret, hidden warmth. Fresh snow can be up to 90-95% air and is a good insulator. In the ‘subnivean’ space 15 cm under the snow, small mammals such as mice and voles inhabit a relatively cozy 0 degrees C space between snow and ground. They are not alone there; in fact an entire foodchain inhabits the subnivean space: bacteria, fungus, springtails, spiders, shrews, weasels etc. Likewise aquatic ‘outwitters’ seek out the relative warmth of deep water zones way below the ice. Cooler water sinks and stabilizes at 4̊ C with no circulation and there it has a higher concentration of dissolved oxygen than surrounding layers. Fish here eat less, move less or, like carp, bury themselves in mud. Some aquatic plants have turions which survive in the 4 degrees C water at the bottom of ponds. These turions, or overwintering ‘buds’, sink, but will outwit winter to rise again in spring, and grow new plants. Dragon flies stay in the water in the nymph stage. Another outwit strategy is ‘Build a four season home’. Bees do this. They consume honey for energy and form tight shivering clusters which are 32 degrees C in the middle. Individual bees regularly rotate position, with bees near the centre trading places with bees on the periphery so there is a better chance for survival. Waste is excreted outside the cluster.
Not surprisingly there are challenges faced by the ‘outwitters’, and some will not survive. Life in the subnivean space is risky. The insulating capability of snow depends on its density. Freeze-thaw cycles compact snow, reducing its insulating ability and allowing dangerous levels of carbon dioxide to accumulate. There is also the threat of hunters of the subnivean space. Foxes can hear prey under the snow and can leap and pounce through. Grey owls can locate prey 2 feet under the snow and plunge through a snow crust that can hold 175 pounds!
While outwit involves taking advantage of subnivean and deep water spaces, or building a four-season home during freezing weather, outlast involves becoming dormant and conserving energy. Or, as Summers described it, “dig deep and stay there”. This is the way of the frog, toad, ant and worm. Earthworms survive 6 feet underground in a slimy membrane. Ants burrow into the soil or under tree bark. Others such as groundhogs, chipmunks, and woodland jumping mice hibernate below the frost. Frogs and salamanders, who can absorb oxygen (O2) and emit carbon dioxide (CO2) through their skin, go deep underwater, as do turtles, who can survive but must dig very deep. Another slogan of the outlast survivors is “It’s better with friends”. Snakes can’t dig but they gather by the hundreds in tree stumps, holes, or in cracks or caves among rocks and share their warmth. Ladybugs do the same under bark and rocks or the south side of a house.
Dormancy or hibernation is another key ‘outlaster’ strategy. In an extreme example, some frogs cryopreserve themselves. As ‘frogcsicles’ their heart is stopped but their organs stay ‘alive’ with no oxygen or nutrients. They survive fatal freezing damage by eliminating water from inside their cells; no ice is formed inside their cells because, instead of water, cells are high in glucose which does not freeze easily. Box turtles and many insects use a freeze-tolerant mechanism; the arctic woolly bear caterpillar may freeze and thaw seven times before finding conditions right for it to pupate, often a matter of years. Some animals have a unique super cooling ability; using high sugars or sugar alcohols and excreting waste, they can lower their body temperature below freezing without becoming a solid. Mourning cloaks, slugs, snails, gall wasp larvae do this but it is risky if they touch ice or if it gets too cold. Perennial plants outlast winter as well, storing nutrients in roots below the frost line. Trees reabsorb valuable nutrients from leaves before the leaves are shed and form buds before winter. Conifers form protects them from snow load and as their roots go past the frost line for water, valves can shut off if ice is present.
Just as there are risks to outwitting winter, there are also risks when attempting to outlast winter. Turtles hibernating under the mud with their hearts beating only once every few minutes are totally vulnerable if they did not dig deep enough. They will be eaten if found because they will not wake up.
A third winter survivor strategy is ‘outplaying’ winter. Dress for winter, remain active and ‘play’ all winter despite the harsh conditions. Birds increase feathers and down layers, lose bright colours, eat more and spend nights in torpor, with lowered metabolic rates and body temperature. They keep their feet warm with extra feathers, and a heat-exchange blood circulation system. Some birds will tuck alternate legs up inside their feathers to keep them from freezing. “Who needs boots?” says Summers. One well-dressed ‘outplayer’ among the winter survivors is the ptarmigan with feathers around its toes and ankles and projections off its feet that look like mittens. Mammals will increase fur, change color to a dull white fur which has more air pockets for better insulation. They will fatten up with brown fat. Some small mammals like chipmunks and flying squirrels are active in their burrows and often emerge on sunny days. Squirrels are active all winter, as are deer, that ‘yard’ in an area of good browsing and shallow snow. They keep the snow beaten down with their trampling for ease of movement.
Another game of the outplayers says Summers is “Cache and Seek”. Birds, mammals, squirrels will hide (cache) extra food to use in winter. Many birds cache food in the fall and find it later by smell and in some cases by their amazing memory. ‘Bird brains?’ Beavers live in their houses with food stored nearby and muskrats make and live in mounds of vegetation called ‘push-ups’. They also establish food caches and bundle together for warmth. Others, such as weasels continue to hunt. Some owls have lopsided ears which allow them to locate prey through triangulation of sound. As mentioned, a grey owl can locate prey under deep snow and plunge through to catch prey. Another strategy is ‘form an alliance’. Crows roost together. Flying squirrels must nest in groups together. Large ungulates will follow group paths through the deep snow. In cities birds flock to roost near warm buildings or chimneys.
Wildlife expert Patty Summers poses with a highly specialized winter survivor, a Great Grey Owl, following her MVFN talk in Almonte. Photo Pauline Donaldson
Which of these strategies is best? If there was an award for the best winter survivor amongst wildlife, which animal would it go to? At the conclusion of her presentation, Patty Summers, told us that for her, the star of ‘winter survivor wildlife’ is a bird, the golden crowned kinglet. This tiny bird does not enter torpor. It maintains a normal body temperature which is 3̊ C higher than other birds. This ultimate outplayer of winter also manages to find three times its weight in food daily, and may raise two broods per year – a marvel of activity!
Birds Beneath Our Feet?
The Mississippi Valley Field Naturalists’ (MVFN) 2012-2013 public lecture series, Nature Beneath Our Feet, continues March 21 with the sixth presentation, “The changing face of predation on Arctic nesting birds: polar bears, foxes and eagles.” You do not need to be an expert to enjoy the presentations, just possess a curiosity or appreciation for wild nature. Cottagers, hunters, fishermen, canoeists, hikers, campers, artists and seasoned field naturalists alike will find something to interest them as we explore nature. Refreshments are offered at each lecture.
MVFN’s March speaker is Dr. Ken Abraham who is the wetlands and waterfowl scientist of the Wildlife Research Team of the Ministry of Natural Resources in Peterborough and an adjunct professor at Trent University in the Environmental and Life Sciences graduate program. His presentation will focus on ground-nesting birds—primarily geese, ducks and shorebirds—in the Arctic and how predation affects their survival. From predation by polar bears on geese and shorebirds, to the role of foxes and alternative prey in predation on common eiders, to unusual events like eagles taking adult ducks, Dr. Abraham will provide a variety of examples to illustrate predator-prey relations among ground-nesting birds.
Nesting on the ground seems inherently dangerous. While falling out of the nest may not be an issue, you would think ground-nesters and their eggs would be easy prey and easily trampled. In habitats where there are no trees, such as grasslands and the Arctic, the ground is it. What strategies might ground-nesters employ to enhance their chances of producing offspring in such areas? Perhaps they are experts at camouflaging nests or eggs. Laying many eggs in a nest, having more than one clutch of eggs, doing predator distracting displays, or behaving aggressively toward intruders also might help. Can you think of other deterrents?
Some ground-nesting birds select areas where ground predators are less abundant. For example, Dr. Abraham and his colleagues conducted a study of predation and ground-nesting Arctic shorebirds. They put out over 1,500 artificial nests with eggs along a north-south gradient covering almost 30 degrees of latitude (3,350 km). After two summers of investigation, they found that nests at the northern extreme (Alert Island, 82oN) experienced 66% less predation than nests at the southern end of the gradient (Akimiski Island, 53oN, southern-most tip of Nunavut). No wonder Arctic-nesting birds have some of the most impressive migratory strategies, such as flying from wintering areas at the southern tip of South America, southern Africa, and Oceania to their breeding grounds in the Arctic—the reward is fewer predators!
Another strategy ground-nesting birds may use for reducing the risk of predation is to enlist other species to provide some protection. The ‘protector species’ would show aggressive behaviour toward predators or provide early warning signals of predator approach, or both. This strategy was examined by Dr. Abraham in a study that compared nest survival of semipalmated plovers in areas with and without nesting arctic terns. He found that plover nests benefited substantially from protection against predators (<10% of all nests lost) through aggressive behaviour of the terns.
And the story about eagles taking adult ducks? For that you will need to come to Dr. Abraham’s presentation, “The changing face of predation on Arctic nesting birds: polar bears, foxes and eagles,” which will be held at 7:30 pm on Thursday March 21, 2013, Almonte United Church, 106 Elgin St., Almonte. All are welcome ($5 fee for non-members). For further information please contact MVFN’s Program Chair Cathy Keddy at 613-257-3089.
Survivor: Winter Wildlife—Outwit, Outlast, Outplay
Mississippi Valley Field Naturalists February 6, 2013
The Mississippi Valley Field Naturalists’ (MVFN) 2012-2013 public lecture series, Nature Beneath Our Feet, continues February 21 with the fifth presentation, “Survivor: Winter Wildlife—Outwit, Outlast, Outplay.” You do not need to be an expert to enjoy the presentations, just possess a curiosity or appreciation for wild nature. Cottagers, hunters, fishermen, canoeists, hikers, campers, artists and seasoned field naturalists alike will find something to interest them as we explore what lives in Lanark County and how best to protect it for future generations. Refreshments are offered at each lecture.
In this upcoming survivor episode, unlike others with which you may be familiar, the prize is simply survival—cars and money not being much use to wildlife. Further, the drama plays out in all countries experiencing cold winters like those in Canada, not just those seen on television. By contrast, the strategies of wildlife to survive the winter, as speaker Patty Summers will describe, are as seen on TV: outwit, outlast, outplay. Biologist Summers, currently with the Wild Bird Care Centre in Nepean, is a well-known natural heritage interpreter. As part of MVFN’s Environmental Education Program, Patty creates, delivers and is responsible for the success of the organization’s Young Naturalists program. Now, after giving numerous natural history presentations at elementary schools in our area, Patty will give “old naturalists” an opportunity to learn about winter wildlife survival strategies.
Winter brings cold, darkness, wind, snow, ice and, sometimes, rain. We seem to grasp at all three survival strategies: outwit (pray for global warming), outlast (stay inside), outplay (go to Florida), but how does our wildlife (and wild plants, for that matter) cope with these extreme environmental demands? What are the costs or disadvantages of adopting such strategies?
Outwitters—the ones who turn the tables and take advantage of winter conditions to remain active and comfortable—where would you look for them? Owls know where and how to find them. Can you think of some members of this group?
What about outlasters? These organisms have special adaptations for shutting down and simply tolerating winter extremes, reanimating in the spring. Many of you may have heard about amphibians and their adaptations for outlasting winter. Unlike us, they cannot control their body temperature. In ponds they can burrow into the mud so they don’t freeze, but what about those wintering on land?
Outplayers remain active despite exposure to the rigors of winter. Their physical and behavioural adaptations seem virtually unlimited—fur density increase, cooling of blood flowing to extremities to reduce heat loss, higher metabolic rates, creating food caches, and being active only during the warmest period of the day. Oh, and there is more to changing fur colour to white for camouflage—white hairs, without the pigment melanin, have more air spaces within the hairs, conferring greater insulation! Patty will add significantly to these observations, but with illustrated examples.
In which category would you put mice, eagles, sticklebacks, salamanders and yourself?
If you are not sure, ask Patty at her presentation, “Survivor: Winter Wildlife—Outwit, Outlast, Outplay,” which will be held in a nice, warm room at 7:30 pm on Thurs. Feb. 21, 2013, Almonte United Church, 106 Elgin St., Almonte. All are welcome ($5 fee for non-members). For further information please contact MVFN’s Program Chair Cathy Keddy at 613-257-3089.
Which forest is healthier? Lecture report by Christine Hume
Which forest is healthier? If you selected the first one pictured below you are on the right track. At the recent Mississippi Valley Field Naturalists (MVFN) talk “Coarse Meaty Debris: The Significance of Large Dead Animals in our Forests” given by Dr. Paul Keddy, we learned that a forest that has a healthy mixture of living trees, fallen decomposing trees, and dead standing trees is a healthy forest ecosystem. The talk focused on the deciduous forests of eastern North America.
Many of the forests in this area were cut by the end of the last century, so most of the ancient old growth forests are long gone. Slowly our deciduous forests have come back; some of the key indicators to help judge the health of these forests were discussed. The presence of diagnostic species such as spring ephemerals (e.g. Trillium), Wood Warblers and Salamanders are good signs. Additional indicators include: more big trees, canopy composition, a diverse herbaceous layer, wildlife trees, woodpecker nesting trees, and coarse woody debris. The woody debris is a major source of biological diversity, allowing ferns, mosses and fungi to thrive.
It is important for landowners with forested property to understand the benefits of maintaining and managing biological diversity. We learned that it is beneficial to a wide range of plants, animals and insects to let a tree that falls in the woods—just lie there. A general rule of thumb is to leave 8 fallen trees per acre—the bigger the tree the better!
Dr. Keddy then noted that as he was preparing the talk and thinking about the benefits of “woody debris” – the phrase “meaty debris” came to mind. The talk next focused on the importance of “coarse meaty debris” (animal carcasses) and the contribution it makes to a healthy forest. Of particular interest to me, was the description of the simple study conducted by Dr. Keddy and his wife Cathy on their property. On a beaver pond they set up a man-made carcass—a pile of trim (meat and bone scraps) from their local butcher. Then they recorded detailed field notes and observations over a period of 3 – 10 days noting which birds and mammals came to feed on the “carcass”. We were very surprised to learn that the first bird that came to feed on the meaty debris was a tiny little chickadee. It was feeding on the fat of the carcass. Next in the carcass line-up was a couple of crows, then turkey vultures, then a large gathering of crows and ravens; several coyotes and so on. It was a powerful demonstration of the number of species that will feed on carcasses and may depend on the availability of ‘meaty debris’ for survival.
The first bird to visit and feed on the ‘artificial’ carcass was a tiny chickadee. Photo Cathy Keddy
Another study that was conducted in Algonquin Park was presented— the ‘meaty debris’ in this instance included deer and moose carcasses. Species that eventually found the carcasses included: ravens, turkey vultures, fox, black bear, otter, and wolf. Black bears are known to be carrion feeders. There is a huge array of species that feed on carcasses. They are a centre of biodiversity. The bodies are cleaned up—animals may tear, grind, pick, gnaw and disperse pieces of the carcass. Anything remaining goes back into the soil. After a few weeks there is nothing left. Quite fascinating really!
It was also interesting to learn about the 68 species of burying beetles. The beetles bury small carcasses; lay their eggs in the carcass and their young then feed off of it. And then Dr. Keddy presented some examples of how humans can interfere with the circle of life – and keep it from running smoothly.
Given a total deer population for Ontario of 400,000, (estimated by the Ontario Ministry of Natural Resources), the range of deer i.e. covering about 40% of the area of the province, and a natural annual mortality rate of 10%, the natural deer carcass density would be approximately 1 carcass/10 km2. The annual removal of potential carcasses through hunting (60,000 – 70,000, estimated by OMNR) is high relative to the 40,000 animals that naturally become “meaty debris.” The removal of deer by hunting results in a steady drain of carcasses, nitrogen, phosphorus, and calcium from our forests. This probably has a significant negative impact on all the species that feed on carcasses.
And going back 10,000 years Dr. Keddy briefly discussed “megafauna” and the big carcasses of that era, now missing, including: woolly mammoth; sabre-toothed cat; giant ground sloth and more. The cause of the demise of these giant creatures at the end of the last ice age is widely debated. We saw photos of hand-chiseled spearheads that were found along with the remains of some of these gigantic mammals. It is suspected that our human ancestors became a bit too skilled at hunting and likely were largely responsible for exterminating the megafauna.
This talk really made me think of the circle or web of life – and how interconnected and interdependent the trees, plants, mammals, insects are on each other.
How can we contribute to keeping our forests healthy?
Find out what is being done with road kill that is collected? Instead of it being incinerated or disposed of, can some be distributed in managed forests to support a healthier ecosystem? Can some be put where naturalists can observe and learn the effects of meaty debris?
Increase public awareness that dead trees and carcasses in the woods are an essential part of nature— a “good thing,” not something to be offended by— they will be cleaned up by nature itself.
Resources: To learn more about our forests and the Managed Forest Program, check the Ontario Ministry of Natural Resources website at http://www.mnr.gov.on.ca/en/. If you are interested in volunteering and helping with forest management projects, refer to information provided by OMNR, the Ontario Forestry Association (http://www.oforest.ca/) and the Eastern Ontario Model Forest http://www.eomf.on.ca/ . For more information about the research work of ecologist Dr. Paul Keddy, please visit his website at http://www.drpaulkeddy.com/