It’s a typical sight in fishing areas: a trawler or other boat being followed by seabirds eager to gulp down the unwanted fish the crew throws back. Research has shown that the supplemental food such discards provide can affect bird populations, in some cases improving reproductive success.

Now a study has shed light on a different impact of fishing-boat discards. Researchers report in Current Biology that they can affect birds’ patterns of movement on large scales.

Frederic Bartumeus of the Center for Advanced Studies of Blanes, in Blanes, Spain, and colleagues analyzed satellite tracking data for two species of shearwaters on foraging trips off Spain’s Mediterranean coast.