In a nutshell
Animals that migrate are challenged with figuring out the best time to arrive to their breeding grounds to maximize the amount of (usually food) resources available. For Barnacle Geese, this means timing their arrival and breeding so their goslings have the best chance at survival. Scientists have wondered whether their migration relates to the green wave, or the leaf-out of plants across the northern hemisphere. Do the geese follow the peak in nutrient availability created by the green up of plants across the northern hemisphere, or time their arrival at breeding grounds to be early enough for their offspring to capitalize on this increase in nutrients?
An international team of scientists found that Barnacle Geese overtake the green wave, first arriving at the southernmost stopover sites along their migration pathway to fatten up on the peak plant biomass, then arriving at their northern breeding grounds at the local start of spring. If geese arrive before snowmelt, they will actually stop short of the breeding grounds at “staging” sites, where they can still access food resources in areas where snowmelt has occurred and food is growing.
What is special about this study?
The green wave hypothesis is a long-held theory that predicts geese surf the leaf-out of plants on their way from their wintering grounds up to their breeding sites. This study is the first to use field studies to test the idea that geese actually overtake the green wave rather than following the peak in nutrients.
To test this hypothesis, scientists need to be able to measure the green up of plants across the northern hemisphere. In the past, studies like this used vegetation indices and thresholds that were coarse. This study uses satellite imagery with a finer spatial and temporal resolution than previous studies to measure the change of vegetation and estimate the timing of spring onset and peak in nutrient biomass. This new method can be expanded to other animals to compare how migration timing matches with green-up.
What does this mean for YOU?
This information can be used to see whether herbivores that migrate across large areas (such as other birds, caribou, and wildebeest), use a similar strategy for spring migration. Better knowledge of the cues animals use to time their migration can be used to predict the arrival of these animals in the spring as well as mismatch between timing of migration and the phenology of food resources, particularly as plant phenology changes in the face of climate change.
Citation: Si, Y., Xin, Q., de Boer, W.F., Gong, P., Ydenberg, R.C., Prins, H.H.T. 2015 Do Arctic breeding geese track or overtake a green wave during spring migration? Scientific Reports. DOI: 10.1038/srep08749