Seems like love is in the air! Collared Doves, along with other pigeons, are well known for nesting early + recorded every month of the year, though most are spring/summer. As they don't need to find insects to feed their young like many birds they can afford to nest early. As you probably know they are fed on pigeon's "milk" which is regurgitated, semi-digested material from parent's crop- hope you're not eating at present!
Hope they are successful, though early clutches are more likely to fail if inclement weather takes hold.