Peregrine falcon eggs will soon hatch in Uccle!

In 2013 we observed, for the very first time, Peregine falcons present at the Saint Job church in Uccle. A peregrine pair was frequently observed in the spring, but nothing more.

Then the peregrines came back the following spring. Clearly, their behaviour indicates they would like to nest. We are very hopefully but in the end no falcon chick was observed.

2015 is a good year! The pair successfully nested and raised four falcon chicks. A first performance in this municipality located in the south of the Brussels-Capital Region.

Since then, the Peregrine falcons successfully nest every spring in Uccle. The male is the same one since 2015. He was born and ringed in April 2012 on Saint Rombaut's cathedral in Mechelen. The distance between Mechelen and Uccle is 28 km. The female was ringed in the spring of 2016 in Saint Job, at the moment her chicks were ringed. We therefore do not know where and when she was born. But, since she had an adult plumage in the spring of 2016, she must have hatched at least in 2014.

This year, the female Peregrine of Uccle laid her first egg on March 4th. The second was laid on March 7, the third on March 9 and the fourth and last on March 11. A perfect regularity therefore since peregrines normally lay their eggs at 48-hour intervals. This is indeed the minimum time for an egg to form in the female's oviduct. Each egg weighing about forty grams, the female will therefore "produce" more than a tenth of its weight in a few days.

Brooding - or incubation - does not yet begin when the first egg is laid, otherwise the first chick would hatch a week before the last one hatches. As such, the difference in age - and therefore in size - would be enormous between the hatchlings within the brood. This would very likely represent a major difficulty for the parents who would have to take care both of a newborn chick which must be permanently brooded and fed bit by bit, while not neglecting an elder who would begin to ask for different care.

Hatching in Uccle therefore began this spring on March 9th. Exactly as in the spring  of 2021! Since then, the parents constantly relay each other while incubating the eggs (video 1). Among the Peregrines, male and female brood! There is little activity in the nest during this period, except that the brooder always takes great care to turn the eggs regularly. This handling allows a good distribution of the heat in the eggs. But also, prevents the internal membranes of the egg from adhering to each other and hindering gas exchange between the embryo and the outside.

March 9, 32 days of incubation, count, hatching should start this weekend!

Video 1 Male and female relay each other when brooding on the 4 eggs.

Video 2 Birds carefully turn their eggs several times a day.

Video 3 The male, much smaller than the female, still has difficulty covering his 4 eggs.

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