Being a young guillemot chick is quite hard. Growing up on a small ledge on high cliffs in the Arctic, surrounded by thousands of birds, being prey for gulls, foxes and even polar bears is quite stressful. But even worse, the little ones have to jump down into the water before their wings can support them for flight. This behavior has puzzled scientists for a long time. Now, an answer may have been found.

Both Brunnich’s guillemots (right, with white stripe) and common guillemots (left) lay their eggs on rock ledges high above the water. They only overlap in some parts of the Arctic like Chukotka as Brunnich’s are more high Arctic birds than common guillemots. Picture: Michael Wenger
Both Brunnich’s guillemots (right, with white stripe) and common guillemots (left) lay their eggs on rock ledges high above the water. They only overlap in some parts of the Arctic like Chukotka as Brunnich’s are more high Arctic birds than common guillemots. Picture: Michael Wenger

It had earlier been suggested that guillemots offspring headed off to sea once the chicks reached about one-quarter of their adult size and were large enough to defend themselves from potential predators and too large to be fed at the colony. So that this seemingly death-defying behaviour could be better understood as being, in some ways, a tradeoff between the safety offered in the colony and fast growth rates at sea, where more food is available. But after tracking the behaviour of guillemot fathers and their offspring for six weeks in guillemot colonies in some of the most remote locations on the globe, in Nunavut, Greenland, and islands off Newfoundland, scientists have discovered that mortality rates were similar between chicks at sea and in the colonies. Moreover, the team which was made up of researchers from McGill and Memorial Universities in Canada and Aarhus and Lund Universities in Denmark and Sweden discovered that chicks at sea grew at roughly twice the speed of those at the colony, because the guillemot fathers no longer needed to fly back and forth to the colony to feed them.

As summers are short in the Arctic, chicks have to grow fast which means hard work for the parents to provide enough food. Luckily, in the Arctic Ocean, food is highly abundant and the birds don’t have to fly that far. Picture: Michael Wenger
As summers are short in the Arctic, chicks have to grow fast which means hard work for the parents to provide enough food. Luckily, in the Arctic Ocean, food is highly abundant and the birds don’t have to fly that far. Picture: Michael Wenger

Unusually among animals, after three weeks of care by both parents, it is the father who then spends 5 to 7 weeks rearing the offspring by himself on the high seas. Meanwhile, the mother spends her time partying back at the colony, copulating with paramours to choose a potential suitor should her mate not return the next year. The study documented the hard work done by the father. The team recorded males spending up to six hours underwater each day to feed the chick, while the female spent only one to two hours underwater each day. "The Arctic summer is short," says Elliott, who teaches in McGill University's Department of Natural Resource Sciences. "The mother must produce an egg quickly. Murres have the highest flight costs of any animal, and the female works hard at the front end flying back-and-forth to the colony, leaving her exhausted by mid-summer. Nonetheless, we were astonished to see how hard the father worked through late summer, spending virtually every daylight hour diving to feed the chick."

Guillemots breed on small ledges and the chicks are squeezed close to the wall and are protected by their parents. However, they have to jump down eventually before they can fly. Picture: Michael Wenger
Guillemots breed on small ledges and the chicks are squeezed close to the wall and are protected by their parents. However, they have to jump down eventually before they can fly. Picture: Michael Wenger

"Once you know that there are both higher growth rates for the chicks at sea, and similar survival rates compared with life in the colony, it then makes sense to see this seemingly death-defying leap as a win-win strategy when it comes to survival," says Kyle Elliott, the lead author on a paper on the subject that was published online March 8 in The American Naturalist. Elliott teaches in McGill University's Department of Natural Resource Sciences. "We would never have been able to discover this without using the kind of state-of-the-art recorders that are now available and provide a glimpse into the life of murres on the high seas."

Predators of chicks usually are Arctic foxes and glaucous gulls. However, also polar bears have been observed to climb down on the small ledges and snatch chicks straight from their parents who can fly away to protect themselves. Picture: Michael Wenger
Predators of chicks usually are Arctic foxes and glaucous gulls. However, also polar bears have been observed to climb down on the small ledges and snatch chicks straight from their parents who can fly away to protect themselves. Picture: Michael Wenger

Source: McGill University