In the Mi’kmaw calendar, October is Wikewiku’s, or animal fattening month.
This is a time of plenty in terms of food supplies for many animals but that situation will change dramatically as the ground freezes and is then covered with a white blanket of snow. The fat that is accumulated during this time of plenty will sustain the animals that hibernate here all winter and those that undergo long migrations to spend the winter in more southerly climates.
Biosphere birds that are preparing to migrate can undergo impressive weight gains. A migratory bird can fatten up by as much as 10 per cent per day, although the usual rate is more like one to three per cent. Non-migratory passerines (perching birds) maintain a fat load of about three to five per cent of their lean body weight. Migratory passerine birds, in preparation for migration, can attain a fat load of up to 50 per cent. Perhaps my winter physique could be explained by a desire to migrate?
There are several impressive migrators that breed in the Bras d’Or Lake Biosphere, according to the Maritimes Breeding Bird Atlas. In particular, a charming little warbler has caused quite a stir. As reported in the April (2015) issue of the journal Biology Letters, a team of scientists headed by William DeLuca tracked blackpoll warblers on their southerly migration. The tiny birds were fitted with radio tags on Bon Portage and Seal Islands in Nova Scotia and tracked to wintering grounds in Columbia and Venezuela in 2013, a distance of around 2,500 kilometres.
The scientists report that blackpolls undergo one of the longest distance non-stop overwater flights ever recorded for a migratory songbird. However, during this past spring, that record was challenged by another songbird which breeds in the Bras d’Or Lake Biosphere. A student in Ithaca, New York, caught a yellow warbler in June, 2017 that had been banded in Columbia two months earlier. Its’ journey covered a distance of over 3,000 kilometres.
To fuel these migratory journeys, these tiny birds gain a lot of weight quickly. A typical blackpoll warbler at the end of its breeding season weighs about 11 or 12 grams (one-quarter the weight of a chocolate bar). In preparation for its migratory trek, it may accumulate enough fat reserves to almost double its body weight. Its’ in-flight fat consumption rate is about 0.6 per cent of its body weight per hour. In human terms, this fuel strategy would be equivalent to a 68 kilogram person gaining 6.8 kilograms of pure fat per day until tipping the scale at more than double his or her original weight, and then shedding almost one kilogram per hour through vigorous exercise. This is not a strategy that would appeal to most people.
So, why do these migratory birds accumulate more fat than muscle and how does the weight gain happen so fast? Birds have to be light to fly efficiently. Fat is lighter and less bulky than protein, and supplies twice as much energy for its’ weight. The weight gain starts about two to three weeks before the migration journey as a result of a significant increase in appetite and food consumption.
At the same time that the bird is eating more heartily, it is bulking up where it matters. Increased consumption is accompanied by an increase in the size of the bird’s pectoral muscles which power their wings. Changes in the bird’s physiology lead to a greater concentration of enzymes required for fat metabolism. The little birds become flying powerhouses. Some species even change their diets to help their bodies build up fat reserves. Songbirds that normally feast on a steady diet of insects all summer may switch to a diet of the abundant berries which are composed of sugars and lipids, readily converted to stored fat.
The Bras d’Or Lake Biosphere provides breeding habitat for many other impressive migrators. For example, the Arctic tern (in Mi’kmaq: niktulnej) is known to breed in several areas of the biosphere. The terns are seabirds, not songbirds, as any beach goer will recognize. The songbirds are perching birds with the required anatomy to produce beautiful, melodious songs. Seabirds generally do not perch, are adapted to life on and near the ocean, and do not necessarily produce songs. The two groups are aptly named.
The Arctic tern is a popular visitor at several of the Bras d’Or Watch lakeshore sites for the field day in July. The migratory journey taken by this little fish-eater is unbelievable. This bird’s annual migration journey can cover two poles, both north and south! A bonus of this long migration journey is that Arctic terns can see two summers each year as they migrate from northern breeding grounds to the Antarctic coast for the southern summer and back again about six months later. Scientists have documented annual Arctic tern roundtrip lengths of up to 90,000 kilometres, the longest migrations known.
I have a renewed respect for these streamlined acrobats that are so common in some areas of the Bras d’Or Lake Biosphere during the summer.
There are many human migrators who are now preparing to leave for their more southerly winter habitats. However, I don’t believe that they undergo the significant changes in anatomy and physiology nor do they exhibit such impressive athleticism as many of our little biosphere birds.
Dr. Annamarie Hatcher is a consulting ecologist and a board member of the Bras d’Or Lake Biosphere Reserve Association. For more information about the Bras d’Or Lake Biosphere Reserve Association, please visit http://blbra.ca/.