Good evening everyone.
Sorry I have not contributed today, Swenja. I have some family concerns on my mind at the moment. And I'm feeling tired.
Jo, Swenja,
Yes, we have noticed on several occasions that BS seem to be touching their eggs gently on a regular basis. If I remember correctly, UteL was the first to point it out to us, several years ago.
At the time, some responses were that they probably step on their eggs by accident, that BS probably don't see well at close range (don't have good depth perception).
Personally, I don't believe that. Black storks can catch a bumblebee with great accuracy. They grab it with the tip of their beak in the blink of an eye. And they certainly need excellent close-up vision when fishing or catching a snake (right behind its head to avoid being bitten!).
So there is a clear difference between the times they indeed accidentally step on their eggs (e.g. when they walk backwards, or when there is turmoil on the nest because of a threat), and the times they very carefully put their toes on the eggs.
As always, it is easier to observe a behaviour than to explain why they behave as they do. I remember there was a study that pointed out that birds have very sensitive legs and feet. Because developing chicks have a metabolism and thus produce heat, and because fetuses have a heartbeat, it would not surprise me personally if Black Storks can indeed feel whether the chicks are developing well. Or at least whether an egg contains a living chick or not.
It has been a long time since I looked up any scientific literature on the subject. I should give it another try.
In all these years of observation, my wonder and deep admiration for what Black Storks are capable of has only increased.
I would like to thank you sincerely for all the great work you do,
Swenja!
