Climatic change explains much of the 20th century advance in laying date of Northern Lapwing Vanellus vanellus in The Netherlands

Long time series allow us to look back in time and examine how birds responded to changes in their environment. During the second half of the 20th century, not only did Northern Lapwing Vanellus vanellus experience an increase in spring temperatures, their meadow habitat also changed dramatically due to agricultural intensification. In The Netherlands, eggs of Lapwing have been collected for consumption for ages, especially in the province of Fryslân, and as the finding of the first egg of the season has been an important social event till today, first egg dates are archived. Here we present data on the dates at which the first egg of the season was found in Fryslân, in 1897–2003. Somewhat to our surprise we found that the advance in the first egg date was primarily explained by increasing spring temperatures. Lapwings also laid earlier after wet winters, with little variance remaining to be explained by habitat changes. Still, at the same spring temperatures and winter rainfall, the first egg was laid on average three days earlier in 2000 compared with 1900. A complementary dataset on the date that the first egg was found in the 10th successive Friesian municipality, confirmed the strong effect of temperature and the additional effect of winter rainfall. The number of days between the first egg date for the province and the 10th municipality yielded a measure of breeding synchrony. The start of egg laying was more synchronous during cold springs. Our analysis thus shows that Lapwing laying date was primarily affected by climatic factors rather than by the considerable changes in breeding habitat.