Abstract
We examine the potential selective importance of predation danger on the evolution
of migration strategies of arctic-breeding calidrid sandpipers. Adult calidrids truncate
parental care for reasons not obviously related to levels of food abundance on the
breeding areas or at migratory stopover sites, suggesting that a different trade-off
occurs between providing additional care and adult survivorship. The southward
migrations of adult western sandpipers precede those of migratory peregrine falcons
by almost a month. By moving early and quickly, adults remain ahead of migrant
falcons all the way to their non-breeding areas, where they rapidly moult flight
feathers. They complete the moult just as falcons arrive in late September¿October.
By migrating early, they avoid exposure to falcons when they are unusually vulnerable,
due to the requirements for fuelling migratory flight and of wing feather moult.
Juvenile western sandpipers migrate south just as falcon numbers start to increase,
but do not moult flight feathers in their first winter. Pacific dunlin use an alternative
strategy of remaining and moulting in Alaska after falcons depart, and migrating to
their overwintering sites after migrants have passed. East of the Rocky Mountains,
the southbound migration of falcons begins 4¿6 weeks later. Southbound semipalmated
sandpipers make extended migratory stopovers, but their lengths of stay
shorten prior to falcon migration to the sites in September. Predation danger also
may affect the evolution of migration routes. Southbound western sandpipers fly
directly from Alaska to southern British Columbia, in contrast to the multi-stage
journey northward along the Alaska panhandle. We estimate that a direct flight
would be more economical on northward migration, but may be avoided because it
would expose sandpipers to higher mass-dependent predation danger from migratory
falcons, which travel north with sandpipers. By contrast, few raptors are present in
Alaska during preparation for the southward flight. A temporal and spatial window
of safety may also permit semipalmated sandpipers to become extremely vulnerable
while preparing for trans-Atlantic southward flights. Danger management may
account for the these previously enigmatic features of calidrid migration strategies,
and aspects of those of other birds.
Original language | English |
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Pages (from-to) | 303-319 |
Journal | Oikos |
Volume | 103 |
Issue number | 2 |
DOIs | |
Publication status | Published - 2003 |
Keywords
- migrant semipalmated sandpipers
- arctic-breeding sandpipers
- optimal avian migration
- knots calidris-canutus
- optimal fat loads
- western sandpipers
- raptor predation
- autumn migration
- bird migration
- shorebird migration