Effects of predation danger on migration strategies of sandpipers

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.

Differentiation of tundra/taiga and boreal coniferous forest wolves: genetics, coat colour and association with migratory caribou

“…Whereas random dispersal between different types of habitat will produce gene flow that limits local adaptation (Lenormand 2002), the combination of reduced gene flow and local adaptation facilitated by natal habitat-based dispersal might lead eventually to speciation (Sorenson et al 2003). The results of our study support a critical role for foraging ecology (a factor potentially linked to natal habitat-based dispersal) in explaining genetic and phenotypic patterns in North American wolves that may be similar to patterns in raptors, hyenas and killer whales where resident and migratory prey populations are found (Hofer & East 1993;Hoelzel 1994Hoelzel ,1998Lank et al 2003).…”

Interannual differences in the relative timing of southward migration of male and female western sandpipers (Calidris mauri)

“…." Myers evidently associated 'risk' with the challenges of accumulating large energy reserves, but the idea that the risks stem from the danger posed by predators during or after migration (Lank et al 2003) fits well into this basic hypothesis. However, neither Myers (1981) nor Reynolds and Székely (1997) explicitly considered predation danger as a possible cost of extended Arctic residence for longdistance migrants.…”

“…She concluded that the case was strongest for the escape performance hypothesis, which states that female (both adult and juvenile) western sandpipers have relatively poor escape performance due to their larger size. They therefore terminate arctic residence sooner than do males in order to migrate southward earlier in the face of seasonally-rising predation danger (see Lank et al 2003, their Fig. 3).…”

Predation in bird populations

“…The same applies to studies that correlate natural variation in predator abundance with prey population changes. For example, it may only take one Peregrine hunting on an estuary for 10,000 Western Sandpipers Calidris mauri, to avoid whole sections of the estuary, or even the estuary entirely (Lank et al 2003;Ydenberg et al 2004). If there were 10 Peregrines, for example, the effect would be the same.…”