This is Telyn's 8th consecutive hat-trick of eggs spanning back to 2018 (the first two with Monty) with all three eggs hatching each year except 2020 and 2023 when one egg failed to hatch (around 10% of all bird's eggs don't hatch for various reasons)

These are the earliest ever eggs/hatchings we've had at the Dyfi nest; here are the hatching dates:

• 🐣 17th May at 16:22 (38.1 days)
• 🐣🐣  18th May at 13:15 (36.0 days)
• 🐣🐣🐣 21st May at 15:29 (36.0 days)

You may remember in the last blog - To Delay or Not Delay - I spoke about Telyn's incubation strategy and the fact that we were pretty sure she did not employ a delayed this year, i.e. a conventional standard strategy..

Well, this is exactly what we saw when it came to hatching, a predictable longer span between three chicks hatching - a whole four days in fact.

Here's chick 3 finally managing to enter the world after a marathon 24-hr egg pip-fest:

Delayed Benefits 

So here is a summary of delayed vs standard incubation strategies:

• Delayed Incubation: Ensures a more synchronous hatching meaning chicks hatch closer together in time. This minimises having a runt or weaker third chick.

• Standard Incubation: Incubating immediately after Egg1 is laid results in a longer span between chicks hatching, but the upside is that there is less risk of a DNH - Did not hatch

Here's the way I tend to think about this: both strategies have risks, just at different stages of the breeding cycle. Delaying incubation brings forward the risk to just after laying in the form of increased chance of a DNH. By incubating immediately, however, the DNH risk is reduced but is now shifted towards the chick phase of the cycle with offspring having un-equal fitness (at least to start with).

Off the Charts

Here's a really simple and elegant chart showing the chick hatching timespans of all years where all three have hatched. 

Nora was a 'delayer', Glesni was not. 

Glesni's three chicks took, on average, double the time to hatch after Chick 1 than Nora's did (2.1 days vs 4.5 days).

There's no cause-and-effect illusion happening here, by monitoring our birds 24/7 every year it is pretty obvious which years the female decides to incubate immediately - or not - just by looking at the nest.

I theorised in the last blog that some female ospreys may be able to decide on an incubation strategy on the fly - pun intended.

Telyn would fall right in this category. Early on (2018 and 2019) she delayed incubation, whereas this year and in 2021 she incubated immediately. Pivoting between strategies like this, probably based on environmental conditions at the time (time of year, partner fitness, temperatures etc), could (potentially) greatly benefit overall fecundity success (amount of chicks over time).

I've never seen this behaviour described before in science. I'm certainly not claiming to have witnessed a behavioural strategy first here, but it looks compelling, with supported data (albeit a small sample size) and is borne out in the charts.

It would certainly be interesting to go back over time and measure these environmental metrics just pre-laying. Are there any patterns? Any correlations with either strategy? A PhD right there.

Bobby Bach

So let's discuss all those questions this week regarding the third chick, aka Bobby Bach.

First off, why did he take so long to hatch relative to the timespan between chick 1 and 2?

Well, two main reasons. Firstly we need to consider natural variations between birds, they're not robots. Some chicks may be smaller than others, weaker, pip at a stronger/weaker part of the egg, time of day, and a load of other variables - including a big dollop of luck.

But looking at the data, there is a consistent and measurable delay for Bobby Bachs to enter the world versus their chick 2 predecessor. This is common. Normal, in fact.

Here's a chart - again!

This charts plots the hatching spans of chicks 2 and 3 relative to chick 1 hatching.

Notice that chick 3 (dark green) always, without eggception, takes longer to hatch than chick 2 (grey) relative to chick 1.

Why is this?

One reason could be a subtle incubation inefficiency or microenvironmental differences affecting the third egg only. The third egg might have experienced slightly lower temperatures or less consistent warmth due to the female, by the time chick 2 has hatched, spending more and more time feeding and faffing with the other chicks.

There's also a bit of an illusion here. 

Remember the overall egg incubation-hatching chart of the last blog? Here it is again:

Chick 3 does, in fact, take less time to hatch than the other two - just 36 days on average.

The reason for this is simple - Egg 3 is smaller than Egg2 which, in turn, is smaller than Egg 1. So if we control for any delayed-or-not incubation strategy, successive chicks will, all things being equal, take less time to hatch than the one before them.

An ostrich egg will take a lot more time to boil than a chicken egg. Don't try this at home.

Bobby Bach will be smaller and weaker than his siblings, but if prey availability is not a limiting factor, he has a great chance of survival.

Tegid (2016), Dinas (2018) and Teifi (2020) are all back in Wales as adults and are now breeding for themselves. The connection?

They were all third-chick Bobby Bachs. 

Here's Bobby Bach Teifi (Blue KC6) leaving his Dyfi nest for the last time in 2020.