𝐄𝐯𝐨𝐥𝐮𝐭𝐢𝐨𝐧?
Once, the chiffchaff and the blackcap were straightforward migrants. Their short wings carried them to Southern Europe for the winter, then back again, the chiffchaff first, the blackcap following, arriving on the cusp of March and April.
Things are changing.
Some chiffchaffs now winter here in Belgium, no longer seeking the relative warmth of the Midi or Iberia. The advantage is clear. They are on site earlier, first to claim territory, first to breed.
It is unlikely this began as a conscious shift. More likely a few always stayed, most perishing in harsher winters. Now, with milder conditions, those same tendencies are rewarded rather than punished.
Whether driven by climate alone or by inherited behavioural variation, the result is the same. Their habits are changing. Perhaps the migrants will, in time, be edged out by the remainers, there being no room at the inn anymore.
There is an echo here of a much older movement. After the last ice age, birds pushed north, following the retreating ice. Now the shift is subtler, not a march but a hesitation, a decision not to leave at all.
And so the chiffchaff sings earlier each year, and the blackcap will not be far behind.
A link to the song.