All birds lay eggs in May... Right? That’s what is said, but is it true?
We can already say that this is not the case, because not all bird species lay their eggs in the same month. The moment when birds lay their eggs depends on both the bird species and the climate.
First of all, there is a difference between resident birds and migratory birds. Resident birds stay with us during the year, while migratory birds hibernate in warmer places. Many migratory birds only arrive here when many resident birds are already busy building their nest.
Resident birds, like some ducks, lay their eggs as early as February. Blackbirds and sparrows start in March, tits start around 1 April.
There is a difference in migratory birds, too. Storks, for example, have already arrived in March and they are already brooding at that point. The arrival of the swallow is traditionally the sign that spring is in the air. These birds return between the end of March and May. Brooding starts as early as April. Other migratory birds, like the cuckoo, the golden oriole and the spotted flycatcher, return the last ten days of April and start building at the start of May.
Birds of prey, like the tawny owl, do not depend on insects that are abundantly present in spring, so they already lay their eggs in February.
Global warming plays an important role here, too. When spring is warmer, there will be many insects earlier on in the year. Insect-eating birds, like the blue tit, have to ensure that their young grow up when the most food is available. They will therefore lay their eggs earlier when spring is warmer. For example, it was calculated that the blue tit on average broods 10 days earlier now than 30 years ago.
Birds are more in danger here, because they react quicker to a temperature increase; they do not wait for a more stable higher temperature. By doing so, they could experience a food shortage, because their food, the caterpillars and other insects, do need a longer stable period. That is why it is always useful to keep feeding in your garden!