December 18, 2018, Norwegian University of Science and
Technology
Willow tits (Poecile montanus) generally reside in one territorial area
throughout their adult lives. But brutal winters in the north kill off many of
them. They aren't able to manage well on their own, and storing seeds in the
autumn is not always enough. For the young of the year, it is absolutely vital
to find a flock to spend the winter with. Juvenile birds also have to try to
become high-ranking members within the flock.
Professor Emeritus Olav Hogstad
at the Norwegian University of Science and Technology (NTNU) has banded and
followed willow tits in the Budal area in Trøndelag county from 1986 to 2014.
He has observed both mated pairs and single birds and has compared their survival. Hogstad and Professor
Emeritus Tore Slagsvold at the University of Oslo have now jointly published
their results in the journal Ornis Norvegica, published by the Norwegian
Ornithological Society.
The period after fledging is a
dangerous time for young birds. This is a time when the offspring are driven
away from their kin and forced to move out of the territory where they were
born. "The youngest birds, this year's offspring, experience much higher
mortality than the older generations," Hogstad says.
The young birds need to find
a flock to be part of, but
there isn't room for everyone. Joining a flock, with the hope that they can
take over the territory some day, is their ticket to survival. Survival is also
linked to early flocking. Birds that manage to establish their place in the
flock in the early autumn have much better odds of attaining a higher social
rank, and thus of surviving. Body size does not seem to play any part in
survival. Birds in a flock can learn from each other, and more birds are available
to detect enemies like a hawk or an owl.
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