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81.
It has been argued that the body mass levels achieved by birds are determined by the trade-off between risks of starvation
and predation. Birds have also been found to reduce body mass in response to an increased predation risk. During migration,
the need of extra fuel for flights is obvious and crucial. In this study, migratory blackcaps (Sylvia atricapilla) were subject to an experimental stopover situation where the predation risk was manipulated by exposure to a stuffed predator.
Blackcaps that perceived an imminent risk of predation increased their food intake and fuel deposition rate during the first
period of stopover compared with a control group. The pattern of night activity indicates that birds that were exposed to
the predator also chose to leave earlier than birds in the control group. Since there was no cover present at the stopover
site, birds might have perceived the risk of predation as higher regardless of whether they were foraging or not. Under such
circumstances it has been predicted that birds should increase their foraging activity. The findings in this study clearly
indicate that birds are able to adjust their stopover behaviour to perceived predation risk.
Received: 8 January 1997 / Accepted after revision: 11 April 1997 相似文献
82.
Louchart A 《Die Naturwissenschaften》2008,95(12):1109-1119
During modern birds history, climatic and environmental conditions have evolved on wide scales. In a continuously changing
world, landbirds annual migrations emerged and developed. However, models accounting for the origins of these avian migrations
were formulated with static ecogeographic perspectives. Here I reviewed Cenozoic paleoclimatic and paleontological data relative
to the palearctic–paleotropical long distance (LD) migration system. This led to propose a new model for the origin of LD
migrations, the ‘shifting home’ model (SHM). It is based on a dynamic perspective of climate evolution and may apply to the
origins of most modern migrations. Non-migrant tropical African bird taxa were present at European latitudes during most of
the Cenozoic. Their distribution limits shifted progressively toward modern tropical latitudes during periods of global cooling
and increasing seasonality. In parallel, decreasing winter temperatures in the western Palearctic drove shifts of population
winter ranges toward the equator. I propose that this induced the emergence of most short distance migrations, and in turn
LD migrations. This model reconciliates ecologically tropical ancestry of most LD migrants with predominant winter range shifts,
in accordance with requirements for heritable homing. In addition, it is more parsimonious than other non-exclusive models.
Greater intrinsic plasticity of winter ranges implied by the SHM is supported by recently observed impacts of the present
global warming on migrating birds. This may induce particular threats to some LD migrants. The ancestral, breeding homes of
LD migrants were not ‘northern’ or ‘southern’ but shifted across high and middle latitudes while migrations emerged through
winter range shifts themselves.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献