🐣 - Chick 1 Hatches at 01:35 on 21st May

🐣🐣 - Chick 2 Hatches at 07:37 on 22nd May

🐣🐣🐣 - Chick 3 Hatches at 05:31 on 24th May

Telyn has laid three eggs every year since she started at the Dyfi and all three chicks have hatched in five of those seven years. That is some record.

The 2024 eggs hatched in sequence, the gap between all three chicks being just over three days (half the time it took to lay them).

For reference, below is the Dyfi family tree, this is our 15th year of successful breeding. The list bottom left is of all our offspring that have been spotted having returned as adults, the green ones have, or are, breeding for themselves:

Note that of the nine birds having been sighted back, only two of them are female - that's just 22%.

This is typical of ospreys - the males are much more easy to spot, especially if the returning females are sitting on eggs or tending to chicks for several months. There will be a lot more females out there, they're under-recorded. 

I'd estimate that between 50-60% of birds that leave here in late summer make it back as adults two to three years later.

Intruding ospreys

Talking of returning birds, we've sighted six ringed ospreys intruding on the nest so far this season - and many more unringed ones. The latest is Blue 7C1, a two-year-old female from Cumbria.

Here's a list of all six so far, including one of Merin's daughter and Blue 24's son, Roli. More will come.

Delayed Incubation

As you may remember from the last blog, we did not see Telyn employing her usual delayed incubation strategy this year. She incubated her eggs almost immediately, which is a change from the norm. This is the first time she has done this.

We've only seen Glesni do this before.

The hypothesis is that by delaying incubation until the final egg is laid, the chick development clock would start then, ensuring the chicks hatch closer in time than when they (eggs) were laid.

Below is a chart of all the three-chick broods we've had at this nest dating back 15 seasons, the numbers represent the time, in days, between chick 1 and chick 3 hatching.

So it seems Telyn did not incubate immediately with a 3.2 day span between all the chicks hatching - higher than her average. But clearly she must have incubated a little bit as the chicks still all hatched in roughly half the time it took her to lay the eggs (approx six days).

I love this chart. It elegantly shows two incubating strategies in play between three females. Glesni incubated immediately, with an average hatching span of 4.5 days. Both Nora and Telyn employed a delayed incubation strategy, resulting in a foreshortened hatching span of 2.1 days and 2.7 days respectively - essentially halving Glesni's hatching span.

Pros and Cons

So if delaying incubation seems so advantageous, why don't all female ospreys do it and the strategy is selected ubiquitously into the population by Natural Selection. There must be a downside to delayed incubation?

Indeed there is. 

Both strategies exist in what we call a 'ecological frequency dependent' stasis on a population level - both being approximately as successful as each other. The downside of the delaying is two-fold:

1. Increased risk of predation (eggs exposed)
2. Increased risk of arresting completely chick development due to temperature changes (eggs exposed)

As I write today, all three chicks are thriving - and yes, even Bobby Bach is getting enough to eat.

They (almost) always do.

Here's a short video of all thee 2024 chicks hatching: