Animal migrations offer a unique opportunity for developing and testing hypotheses about the ecological requirements of different species and the tradeoffs that they make between conflicting life-history demands. There has been relatively little research into the causes and consequences of migrations by fruit bats, despite their potential significance for pollination and seed dispersal. We assessed the causes of one of the most spectacular migrations of fruit bats known: the annual influx of an estimated 5-10 million E. helvum into Kasanka National Park in Zambia. We tested several predictions based on the hypothesis that E. helvum migrates to exploit seasonal variations in food supply opportunistically. Phenological data, feeding observations and monitoring of fruit bat movements provided the first quantitative evidence in support of the hypothesis that the migration of E. helvum in Zambia is driven by food supply. The E. helvum colony exhibited several surprising behaviors, including a tendency for migratory satellite colonies to aggregate, rather than to disperse, during the time of peak food production, and a tendency to fly well beyond the most immediate food sources when foraging. Alternative hypotheses to explain the E. helvum migration were not supported, but further research is needed to clarify the results of this preliminary study. Both the size of the colony and its potential for large-scale movements suggest that this bat may play an important economic and ecological role over a significant portion of sub-Saharan Africa. Information is still lacking about migration routes, food sources, habitat requirements and the role of migration in disease transmission between colonies of E. helvum.
Despite long-standing awareness of the potentially important ecological role of fruit bats, we know little about the ecology of the vast majority of species. Here we report the results of a pilot satellite tracking study aimed at establishing the scale of movement of the straw-coloured fruit bat Eidolon helvum. This was the first ever attempt to track African fruit bats using satellite telemetry. We tagged four bats with solar-charged 12 g satellite transmitters at Kasanka National Park in December 2005 and obtained a combined total of 104 different location fixes over a 149-day period. Before migrating, bats foraged as far as 59 km from the roost in a single evening; by contrast, one migrating individual moved 370 km in one night. Bats travelled an average 29 km day À1 over the period of study, with bats that appeared to be migrating moving north-west from Kasanka at an average 90 km day À1 . The greatest cumulative distance travelled by a single bat was 2518 km in 149 days. The results show conclusively that the straw-coloured fruit bat E. helvum is capable of migrating thousands of kilometres across central Africa on an annual basis, implying that the fruit pulse in northern Zambia is richer than anything on offer in the Democratic Republic of the Congo at the same time of the year.
Gps1 provides a novel molecular polarity cue at the cell division site that guides Rho1- and Cdc42-dependent polarization during and after cytokinesis in budding yeast.
1. Migrating grazers and carnivores respond to seasonal changes in the environment and often match peaks in resource abundance. However, it is unclear whether and how frugivorous animals use phenological events to time migration, especially in the tropics.2. The straw-coloured fruit bat Eidolon helvum, Africa's most gregarious fruit bat, forms large seasonal colonies throughout much of sub-Saharan Africa. We hypothesized that aggregations of E. helvum match the timing of their migration with phenologies of plant growth or precipitation.3. Using monthly colony counts from across much of the species' range, we matched peak colony size to landscape phenologies and explored the variation among colonies matching the overall closest phenological event.4. Peak colony size was closest to the peak instantaneous rate of green-up, and sites with closer temporal matching were associated with higher maximum greenness, short growing season and larger peak colony size. Eidolon helvum seem to time their migrations to move into highly seasonal landscapes to exploit short-lived explosions of food and may benefit from collective sensing to time migrations. 5. The link between rapid changes in colony size and phenological match may also imply potential collective sensing of the environment. Overall decreasing bat numbers along with various threats might cause this property of large colonies to be lost. 6. Remote sensing data, although, indirectly linked to fruiting events, can potentially be used to globally describe and predict the migration of frugivorous species in a changing world.
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