Data from: Migrating bison engineer the green wave

Newly emerging plants provide the best forage for herbivores. To exploit
this fleeting resource, migrating herbivores align
their movements to surf the wave of spring green-up. With new
technology to track migrating animals, the Green Wave Hypothesis has
steadily gained empirical support across a diversity of migratory taxa.
This hypothesis assumes the green wave is controlled by variation in
climate, weather, and topography, and its progression dictates the timing,
pace, and extent of migrations. However, aggregate grazers that are also
capable of engineering grassland ecosystems make some of the
world’s most impressive migrations, and it is unclear how the green wave
determines their movements. Here we show that Yellowstone’s bison
(Bison bison) do not choreograph their migratory movements to the wave of
spring green-up. Instead, bison modify the green wave as
they migrate and graze. While most bison surfed during early
spring, they eventually slowed and let the green wave pass them
by. However, small-scale experiments indicated that feedback from
grazing sustained forage quality. Most importantly, a 6-fold decadal shift
in bison density revealed that intense grazing caused grasslands to green
up faster, more intensely, and for a longer duration. Our finding broadens
our understanding of the ways in which animal movements underpin the
foraging benefit of migration. The widely accepted Green Wave Hypothesis
needs to be revised to include large aggregate grazers that not only move
to find forage, but also engineer plant phenology through grazing, thereby
shaping their own migratory movements.