“Variation in growth drives the duration of parental care: a test of the Ydenberg model”

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Kyle H. Elliott, Jannie F. Linnebjerg, Chantelle Burke, Anthony J. Gaston, Anders Mosbech, Morten Frederiksen, and Flemming Merkel

Solving the mystery of the cliff-jumping chicks: growth not mortality drives the duration of parental care

Why young murres take the plunge off towering cliffs

A father murre (Uria aalge) and his offspring contemplating the leap off high cliffs at Saunders, Greenland.
(Credit: Knud Falk)

Murres (known as ‘guillemots’ in Europe) and their relatives are the only birds to depart the nest when the offspring are only partly grown (other species leave shortly after hatching, or after reaching at least half of adult size). At two weeks of age and one-quarter of adult body size, young murres leap hundreds of meters off of towering cliffs to follow their fathers to the sea, where they spend the next several years of their life. Why do these tiny chicks make this remarkable leap? Almost 30 years ago, Ron Ydenberg suggested that the behaviour was a tradeoff between safety in the colony and faster growth rates at sea. Once offspring are large enough to defend themselves and too large to be fed at the colony, they head off to sea.

Just after the jump: a father who lost his offspring during the leap off the cliffs followed by another father whose chick survived the descent.
(Credit: Kyle Elliott)

To test this idea, a group of researchers from McGill, Memorial, Aarhus, and Lund Universities spread out across the Canadian and Greenlandic Arctic to visit five murre colonies in some of the most remote locations on the globe. They equipped murre fathers with electronic recorders that reported their activity at sea. Surprisingly, mortality rate was similar at the colony and at sea. However, without the need to fly back and forth to the colony, murre fathers were able to feed their offspring far more than at the colony, and the offspring grew roughly twice as fast. A simple model shows that such strategy could evolve without a tradeoff between safety and growth. Rather, higher growth rates at sea coupled with a positive relationship between growth rates and post-departure survival are sufficient to select for such a strategy. The work uses state-of-the-art technology to answer a long-unresolved question in ecology, and provides a glimpse into the life of murres on the high seas. Read the Article