Scientists have tracked the movement patterns of seabirds off the coast of Spain and found they are directly tied to the schedule of fishing boats. Specifically, when the fishing boats are working during the week, the birds follow them and eat leftover fish. On the weekends, however, the birds revert to their traditional method of foraging: moving from area to area in search of fish. The result is a large scale impact on bird movement.
Frederic Bartumeus, from Princeton University and Institut Català de Ciències del Clima in Spain, and colleagues analyzed the movement patterns of two species of shearwaters on foraging trips using satellite tracking data in a study recently published in Current Biology.
On holidays and weekends, when trawlers are prohibited from fishing in the region, the seabirds spread out in search of food. As time passes, the birds distance themselves further and further from one another in an attempt to find more food sources. On fishing days, however, the birds begin their foraging by spreading out but eventually come together as time passes. It seems, then, that on work days, the birds have a rough idea of where the boats will be located and go there to find food.
The scientists suggest that these supplemental food stocks have a large scale impact on bird movement as well as on breeding performance. That is, since the birds spend less time in search of food, they can increase the frequency of return trips to the colony.
The researchers suggest future research be conducted regarding the effects of local human activities on the spreading properties of animals, such as disease transport. Says Bartumeus in a ScienceDaily article:
We show that human activities in the natural environment can promote critical transitions in the spreading properties of foraging animals by locally changing the predictability and availability of their resources. Our study suggests an elementary but often disregarded connection between human local resource exploitation and global movement patterns of organisms.
Read more in The New York Times.
Bartumeus, F., Giuggioli, L., Louzao, M., Bretagnolle, V., Oro, D., & Levin, S. (2010). Fishery Discards Impact on Seabird Movement Patterns at Regional Scales Current Biology, 20 (3), 215-222 DOI: 10.1016/j.cub.2009.1