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Migrating birds often alternate between flight steps, when distance is covered and energy consumed, and stopover periods,
when energy reserves are restored. An alternative strategy is fly-and-forage migration, useful mainly for birds that hunt
or locate their prey in flight, and thus, enables birds to combine foraging with covering migration distance. The favourability
of this strategy in comparison with the traditional stopover strategy depends on costs of reduced effective travel speed and
benefits of offsetting energy consumption during migration flights. Evaluating these cost-benefit effects, we predict that
fly-and-forage migration is favourable under many conditions (increasing total migration speed), both as a pure strategy and
in combination with stopover behaviour. We used the osprey (Pandion haliaetus) as test case for investigating the importance of this strategy during spring and autumn migration at a lake in southern
Sweden. The majority, 78%, of passing ospreys behaved according to the fly-and-forage migration strategy by deviating from
their migratory track to visit or forage at the lake, while 12% migrated past the lake without response, and 10% made stopovers
at the lake. Foraging success of passing ospreys was almost as good as for birds on stopover. Timing of foraging demonstrated
that the birds adopted a genuine fly-and-forage strategy rather than intensified foraging before and after the daily travelling
period. We predict that fly-and-forage migration is widely used and important among many species besides the osprey, and the
exploration of its occurrence and consequences will be a challenging task in the field of optimal migration. 相似文献
2.
Arseny Tsvey Victor N. Bulyuk Vlad Kosarev 《Behavioral ecology and sociobiology》2007,61(11):1665-1674
How migratory birds decide when to leave a stopover site is important to the understanding of bird migration strategies. Our
study looks at how body condition and the weather affect the decision to depart on nocturnal migratory flight. During two
autumn migration seasons (2002–2003), we radio tracked 51 first-year European robins, Erithacus rubecula, at a stopover site on the Courish Spit (Eastern Baltic) from the first day after landing until their migratory departure.
The tagged robins stopped over for 1–14 days. There was no clear relationship between stopover duration and energetic condition
on arrival. Weather conditions (wind, precipitation, and cloud cover) on departure differed measurably between years. In 2002,
robins took off mainly under following winds and clear skies. In 2003, there were mainly light head winds and partially cloudy
or overcast skies. This could be explained by the year-specific role of weather factors in making the decision to depart.
In both years, robins making short (1–2 days) stopovers took off in more varied weather situations than those individuals
with long stopovers. This suggests that robins from the former group were more inclined to continue with migration than longer-stay
birds that, apart from re-fuelling, could be waiting for favourable weather. The lack of a relationship between stopover duration
and body condition and some departures under unfavourable weather conditions suggest that endogenous spatiotemporal programmes
may play an important role in controlling stopover duration in robins. 相似文献
3.
Wind selectivity of migratory flight departures in birds 总被引:5,自引:0,他引:5
Optimal migration theory predicts that birds minimizing the overall time of migration should adjust stopover duration with
respect to the rate of fuel accumulation. Recent theoretical developments also take into account the wind situation and predict
that there is a time window (a set of days) during which birds should depart when assisted by winds but will not do so if
there are head winds. There is also a final day when birds will depart irrespective of wind conditions. Hence, the wind model
of optimal migration theory predicts that birds should be sensitive to winds and that there should be a correlation between
departures and winds blowing towards the intended migration direction. We tested this assumption by tracking the departures
of radio-tagged passerines during autumn migration in southern Sweden. Our birds were moderately to very fat when released
and therefore energetically ready for departure. There was a significant correlation between direction of departure and wind
direction. We also found that during days when birds departed there was a significantly larger tail wind component than during
days when birds were present but did not depart. Our results show that passerines do take the current wind situation into
account when departing on migratory flights. We also briefly discuss possible clues that birds use when estimating wind direction
and strength. The inclusion of wind is an important amendment to optimal migration theory of birds and should be explored
further.
Received: 1 March 1999 / Received in revised form: 4 October 1999 / Accepted: 16 October 1999 相似文献
4.
Birds migrating along coastlines may be at increased risk if displacement occurs toward open-ocean. Eastern North America
experiences prevailing northwesterly winds during autumn, which could compel some migrants to drift eastward. Therefore, migrants
at stop-over sites along this route may be a mixture of on- and off-course individuals. We assessed whether orientation behavior
of juvenile yellow-rumped warblers (Dendroica coronata) captured at a stop-over site in southern Nova Scotia was related to where they originated from (i.e., likely on/off-course).
We hypothesized three scenarios after displacement: 1) continued orientation in the migratory direction selected before displacement,
2) orientation from the new location toward the previous destination, or 3) correction to regain the original pathway. Using
stable isotopes, we determined that stop-over migrants originated from nearby areas (and assumed on-course) and as far away
as western Hudson Bay, over 1,600 km northwest (and assumed off-course) of the site. We used video-based orientation registration
cages to determine an individuals’ migratory orientation. Because numerous factors influence migratory orientation (e.g.,
fuel reserves, celestial cues), we simultaneously assessed the influence of body condition and cloud cover, in addition to
geographic origin, on orientation behavior. Individuals that originated closer to the site tended to orient more southwesterly.
Orientation directions became increasingly more west-northwesterly the further away an individual originated from the site
(i.e., the more likely it was to have been displaced). The result is most consistent with scenario three: individuals from
northwest origins likely respond to easterly displacement by orienting westerly to reestablish their previous migratory route. 相似文献
5.
Volker Dierschke Bettina Mendel Heiko Schmaljohann 《Behavioral ecology and sociobiology》2005,57(5):470-480
In a field experiment on the island of Helgoland (southeast North Sea), we investigated whether migration strategy or competition between the sexes cause the differential timing of spring migration of male and female northern wheatears (Oenanthe oenanthe) (males migrating earlier). The study included two subspecies, heading towards Greenland/Iceland and Scandinavia, respectively, and is based on colour-ringing and remote weighing of individuals. Despite food offered ad libitum, most Scandinavian birds left the island on the day of arrival or stayed only 1–3 days, whereas more than half of Greenlandic/Icelandic birds stayed for up to 12 days and refuelled rapidly. In the latter subspecies, males showed a positive correlation of departure fuel load and fuel deposition rate, resembling time-minimizers in optimal migration theory. In contrast, females departed irrespective of fuel deposition rate, with an approximately constant level of fuel stores. This level was lower than in males, but sufficient to enable by-passing of stopover sites en route, allowing us to regard females as time-minimizers also. Since females are not able to reach Greenland without additional refuelling elsewhere and males appeared to have a larger potential for by-passing stopover sites, time-selection seems to be more pronounced in males and may be the reason for earlier migration of males. Intraspecific aggressive interactions between colour-ringed birds were predominantly won by the initiator, by males and by larger birds, whereas fuel load and subspecies did not affect the outcome. Although compared to females, males were more often dominant at the feeding stations or held territories, refuelling patterns could not be explained by dominance. Subordinate or non-territorial birds did not refuel at a lower rate or depart with lower fuel loads than dominant or territorial birds. In non-territorial birds, the restricted access to feeding stations was made up with larger doses of food taken per visit, leading to the same energy intake as that of dominant and territorial birds. Therefore, competition during stopover could be eliminated as the reason for differential timing of migration of male and female wheatears, but this result may be species-specific.Communicated by W. Wiltschko 相似文献
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