Shorebird Migration
NEW LIFE IN THE TUNDRA
The two million migratory shorebirds that visit Australia each year are born in the arctic tundra of Russia and Alaska, in meadows within the belt of the northern hemisphere’s boreal forests, or within the rugged deserts and steppes of the middle northern latitudes in places like Mongolia, and northern China. Many shorebirds are born under the care of a male and female who have travelled to the same place year after year to breed. Others are born in the areas where the food was plentiful that year and where either the male or the female mates with many of the opposite sex leaving all the parental care to their many mates. A few are born to families where the male has taken care of one set of eggs, while the female has cared for a second. No matter where they were born, or the kind of family they come from, all have to grow up incredibly fast, before taking on a journey that is virtually unmatched in difficulty.
PREPARING FOR MIGRATION SOUTH
Nearly as soon as a shorebird hatches it can walk around and find its own food. Parental care consists mostly of distracting the occasional predators like arctic foxes or snowy owls, and leading young to patches of food. At only six weeks old the mother often leaves on her journey to the southern hemisphere, and the father often follows a week later. By eight weeks old the chicks are fully grown, without their parents, and must fly south or risk freezing in the coming snows. In a physiological frenzy the young birds may increase in mass by up to 80% until they are 55% fat, packing on the weight at an incredible 2-5% weight gain per day. Imagine a man that weighs 100 kilos putting on 2 to 5 kilos a day until in a couple of weeks he weighed 170 kilograms.
Right before they leave their feeding organs shrink, their heart grows and their blood thickens. Like an overinflated football with wings, they set off south burning that fat at up to 1 gram an hour, flapping constantly as their body, heart, and muscles atrophy.
AN INCREDIBLE JOURNEY
While avoiding aerial hunters and poor weather, the most difficult part of the journey is navigating the huge distances of up to 13,000km with no parents to guide them. They fly non-stop for days at time, and most are only able to make it half way before they need to stop to put on more fat. The areas they stop at need to be rich intertidal ecosystems, a place where their specialised bills can seek out abundant prey beneath the tidal flats.
TRACKING THE REMARKABLE BIRDS
Incredibly, a few shorebirds have been shown to make the flight in one hop. Some Bar-tailed Godwits were tracked flying for nine days straight from Alaska to New Zealand; an amazing 11,000km non-stop trip across the pacific. Such long flights make one believe the evidence which suggests: these birds can rest different parts of their brains independently; they can see the lines of polarity in the sky (like seeing a compass); they can sense those low frequency long distance travelling sounds called infrasound (a sound made by crashing waves among other things); they can navigate by the position of the sun, and moon and the movement of the stars.
DESTINATION AUSTRALIA
At three to four months of age these juvenile birds find a home along the tidal flats, and wetlands of Australia, and it is here that they grow up spending one to five years before heading north again to breed. The adults meanwhile come and go each year packing on the weight before each departure, and most appear to stop on their way north.
An extra refuelling stop on the way north seems understandable given the still cold northern latitudes, and the need to have enough energy to breed successfully. Unfortunately, these critical places used to refuel are being destroyed at an alarming rate, and this appears to be driving both long and short term population declines in migratory shorebirds….