The relationship between yield loss and grazing pressure: implications for goose management

© Nelleke Buitendijk

The relationship between yield loss and grazing pressure: implications for goose management


Many goose species were in decline not so long ago, or even threatened with extinction. Their recovery is a success story for conservation, but it has also led to increasing conflict with agriculture. In her blog, NIOO animal ecologist Nelleke Buitendijk asks how we can find a way to live together with these geese.

Grazing by geese can cause a lot of damage to agricultural crops. Goose management aims to reduce such damages, for example by actively reducing population sizes. An alternative approach is to chase geese away repeatedly in certain areas, encourage them to move to dedicated agricultural land where they are left in peace (so-called accommodation areas). However, many of the goose species that now occur in large numbers were threatened with extinction only a few decades ago, and are still protected. We therefore need to be sure that a particular management approach will result in a decreased impact on agriculture, before applying it, especially when the approach can have a negative effect on the species in question.

We looked at the relationship between assessed damages on agricultural grassland and the number of geese, to help us understand how changing the number of geese in an area can affect yields. We included barnacle, white-fronted and greylag geese in our study, and focused on the first harvest in accommodation areas in Fryslân, the Netherlands. The Dutch Center for Field Ornithology (Sovon) provided detailed monthly goose counts, which we combined with tracking data from geese we equipped with GPS-transmitters. We received reports on assessed damages from BIJ12, who handle compensations for fauna damages in the Netherlands.

More geese may not always lead to more damage

Our study in Journal of Applied Ecology shows that yield loss is higher when there are more barnacle geese, but the two do not increase at an equal rate: for every extra barnacle goose added to a field, the subsequent extra damage is a little less. This means that concentrating geese in accommodation areas might result in lower overall yield losses, while population reduction may not be an effective tool to lower damages.

The relationship also depends on the presence of other goose species, with highest damages occurring when there are only barnacle geese on a field. In the region we studied, white-fronted and greylag geese have little effect on the assessed losses to spring harvests. This is likely because these species start their migration to the breeding grounds much earlier than barnacle geese, well before the time of first harvest.

Nelleke Buitendijk
Three possible relationships between estimated damage and the number of barnacle geese (represented by grazing pressure), depending on the presence of other goose species. Damage per goose is smaller when barnacle geese are more abundant.

Different feeding preferences

We also see that large flocks of barnacle geese do not occur together with large numbers of white-fronted- and greylag geese. This is likely because the species have different food preferences. Barnacle geese have a small bill, and can easily handle short grass, which is more difficult for the two larger species. However, the larger white-fronted and greylag geese have the benefit of a longer digestive tract, which helps to digest tough foods avoided by smaller species. This means that an area suitable for one goose species, may be unattractive to another.

It may even be that larger species are pushed out of areas where barnacle geese are abundant, because the grass has been grazed too short. A study in Norway also observed this, with larger pink-footed geese leaving areas where large numbers of barnacle geese had moved. This could force large goose species out of safe accommodation areas, if these areas are too small to accommodate multiple goose species. Subsequently, the larger species would suffer more from active scaring or derogation shooting (i.e., chasing geese away by shooting at them, under permit) outside of refuges, while potentially contributing less to agricultural yield loss.

Nelleke Buitendijk
White-fronted geese (left) and greylag geese (right) in Fryslân

Implications for management of wild herbivores

Our results show that we need to be careful with management practices such as population reduction or active scaring. These can negatively affect the animals in question, while not necessarily reducing yield loss. It is also important to ensure management targets the right species; some species may affect yields much more than others. Finally, to make sure all species can find refuge, accommodation areas should represent feeding grounds of multiple species, and should be large enough to prevent competition between them.