Due to warmer springs in recent years, butterflies appear earlier and birds lay their first egg earlier in the year.
Butterflies appear earlier
Over the past 14 years, the first appearance of early butterflies, such as wall brown, green hairstreak and small white has been advanced by an average 9 days. The green hairstreak’s first appearance was advanced by no less than 15 days. The date of first appearance is strongly affected by temperature. So premature appearance is probably the result of warmer springs.
First appearance butterflies
First egg laid earlier in the year songbirds
Early appearance of butterflies is an indication that other groups of insects also appear earlier. Virtually all songbirds - not only insect eaters, but seed eaters as well - depend on insects to feed their young. With food being available earlier in the year, birds start breeding earlier and lay their eggs earlier in spring.
Research proves that egg-laying earlier in the season is a widespread phenomenon. Research among 45 songbird species showed that between 1986 and 2005, the average egg-laying date was advanced by approximately 7 days.
Egg-laying date songbirds
Lodewijk van Duuren, Chris van Swaay (Vlinderstichting) and Frank Willems (SOVON)