The owl files – Chapter 2: Another curve ball . . .

06 July 2021

Another curve ball .  .  . 

The owls have been doing things very differently this season, and it looks like they haven’t stopped just yet.

Yesterday evening I waited for the female to leave the box so that I could check on the contents – and there was a second egg! This must have been laid sometime yesterday, meaning that there has been a four-day gap between the laying of the two eggs. Usually this interval is around 24 hours and any longer interval means that the size difference in the chicks in the nest will be even more marked than normal.

This is is the result of the female starting incubation as soon as she lays the first egg and the embryo immediately beginning to develop. Around thirty-one days later, the first egg hatches, with subsequent eggs hatching more-or-less at the intervals that they were laid.

If both eggs in the Delta nest are fertile, and if they both hatch successfully, the first chick will be four days older than its younger sibling. Nestlings initially double in size every three days so the second hatchling will be way smaller than the first when it eventually hatches. Cainism – where the first-hatched chick attacks – or simply out-competes its younger siblings is not known in Spotted Eagle-Owls but it will be very difficult for younger chicks to compete and secure enough food.

Interestingly, one of the people following these posts has been monitoring a pair of these owls on the West Rand and they have also started nesting early, and there has also been a four-day interval between the laying of the first and second eggs.

By Geoff Lockwood