Breeding black-tailed godwits affected locally by climate change

What is the effect of climate change on black-tailed godwits? This is what researchers from the University of Oxford and the University of Groningen have been asking. Their findings, published in Global Change Biology, show that climate does affect black-tailed godwits, but only in places where the quality of their breeding habitat – agricultural grassland – is poor.

Many bird species are breeding earlier than 40 years ago, in part due to the fact that spring is arriving earlier in the season. Surprisingly, black-tailed godwits do not appear to be adapting to this shift, and as such are still in their nests when farmers are beginning their grass mowing season. Because black-tailed godwits make their nest on the ground, and their chicks need to hide and find food in the grass, they would benefit from breeding earlier to avoid such disruptions.

Laying date
The researchers from examined data from the last 11 years of godwits breeding in Dutch agricultural meadows. In cold springs, and on fields with the greatest diversity of plants and the highest water level, most eggs hatched and most hatchlings reached maturity. 

Dr Rosemarie Kentie, researcher on the project, said: ‘As we expected, it was clear that black-tailed godwits that nested early in spring had the most young. So, why don’t they lay their eggs sooner? First, we found no relationship between the laying date of the parents and the laying date of their young.'

This means that although black-tailed godwits that hatched early had a greater chance of returning as a breeding bird in the years that followed; they did not lay their eggs earlier as a matter of course. Second, only experienced breeding birds appear to breed earlier if spring is very warm and if they bred early the year before as well. Next step is to discover how a bird becomes an early breeder.

If the temperature keeps rising...
As all climate predictions point towards further global warming, the researchers wanted to assess what the consequences could be. They predict that if the temperature in spring continues to rise at the same speed over the coming 40 years, black-tailed godwits will eventually breed five days earlier. These five days will not be enough to keep up with the predicted climate change in dry fields that used for intensive agriculture, although they keep up in flower-rich moist fields that are managed especially for meadow birds. 

'This research shows that loss of habitat quality and climate warming reinforce each other, and, if looking at the future, more account must be taken of this', said Kentie. 

This interaction of habitat and climate change is likely the case for many more species. For black-tailed godwits it means that herb-rich damp meadows will become even more important for the preservation of the species than they already are.