Ageing of Dutch godwit population proving fatal

It won’t be long now before a nesting godwit becomes a rare sight in the Netherlands. Unless, however, stringent measures are taken immediately, according to Julia Schröder, who has done research into fitness correlates of godwits. The main problem is that the numbers of young birds are not increasing enough. Schröder will be awarded a PhD by the University of Groningen on 11 January 2010.

 

Based on current numbers of godwits, Julia Schröder created a simple mathematical population model. Even if the model’s figures are interpreted as optimistically as possible, according to Schröder the godwit’s future looks bleak. ‘We know that the godwit is doing poorly in the Netherlands, but up to now the extent of the problem has been masked by the long life of mature birds. Because hardly any young birds are being born, the population is ageing and will ultimately dwindle. If we want to keep this wader, something really must be done about this.’

Earlier laying date

One of the things Schröderinvestigated was how godwits spend their time during the year and what consequences this has. In the Netherlands in the past, godwits would nest in marshes and boggy wetlands. However, in the first half of the twentieth century many of these areas were transformed for agricultural uses. The godwits adapted to the situation and began to nest in cultivated fields. The godwits also began laying earlier and earlier, up until the 1970s. Schröder: ‘They probably did this in reaction to certain agricultural activities that took place where they were nesting, such as mowing. Because these agricultural activities take place earlier and earlier in the year, you would expect this to also hold true for the laying date; my research, however, has shown that this isn’t the case. Perhaps they have now come up against a limit.’

Cautious strategy is unfavourable

Godwits behave in the manner predicted by the theory for long-lived birds: they maximize life fitness by maximizing adult survival. This means that in a bad year they will probably not breed and delay reproduction until another, better year.

However, the changes to godwit breeding grounds in the Netherlands are not incidental but structural. Mowing takes place earlier and earlier and the climate keeps changing. ‘In such a case, a cautious strategy can have an unfavourable result for birds that invest more in their own survival than in reproduction and in raising offspring since that better future may never arrive,’ according to Schröder.

Improving matters

In order to improve matters for the godwit in the Netherlands, Schröder finds that we should either attempt to improve chances of survival or to improve chances of reproduction. Improving chances of survival is difficult for the godwit, as adult godwits are already long-lived. So the aim must be to increase the numbers and survival of chicks. According to Schröder, halting the backward trend in the Dutch godwit population is only possible if major investments are made.

Economic consequences

Schröder: ‘Given the demands of the current agricultural economy and politics, it’s doubtful that we will be able to take the necessary measures to stop the decline of the godwit in the Netherlands, or to at least slow it down. If we do want change, we will have to accept the economic consequences and act quickly and surely – before it’s too late. 

Feminine male successful

A second focus in Schröder’s research was a classic theme in evolutionary theory: plumage. In the past 150 years, male godwits – who are more colourful than the females – have become paler. Schröder: ‘This is an unusual development, as it’s the opposite of what you would expect. Usually, more colourful males are better males. Potential partners use precisely this fact in selecting a mate.’

Why male godwits’ plumage is becoming paler is not completely clear. Schröder: ‘Females that have mated with paler males lay larger eggs with a better survival rate. Males that look more like females thus are more successful these days than their more colourful counterparts.’

Less aggressive

Schröder: ‘Due to the fact that over the years the breeding ground of godwits moved from boggy wetlands and marshes to hayfields, they are now able to nest closer together. This makes defence against predators much easier but only if the males are not too aggressive towards one another. The reason that paler males are more successful could be that the competition among them is less of a hindrance for them than for more colourful males.’ 

Curriculum Vitae

Julia Schröder (Germany, 1976) studied biology at the University of Münster and did her PhD research at the Animal Ecology department of the Centre for Ecological and Evolutionary Studies (CEES) of the University of Groningen. Promotor is prof.dr. Theunis Piersma. Her thesis is entitled Fitness correlates in Black-tailed Godwits. Schröder is currently a postdoc at the Animal and Plant Science Department of the University of Sheffield. 

Note for the press

More information: Julia Schröder, tel. +44,114 25 88,687, e-mail: julia.schroeder@gmail.com