Clarach and Cerist have started the greatest journeys of their lives. Clarach left the Dyfi on Wednesday morning, her sister went two days later followed by their father, Monty. The Dyfi is once again osprey-less for another winter.

The last photo of both sisters together, the following morning Clarach (right) had gone.

2013 has been a remarkable year once again for the Dyfi ospreys, but not for weather reasons this time. With Nora not returning this year, it wasn't until May that Monty found a partner and between them they raised two chicks - but right at the very end of the breeding window. They were a good month behind the 'average' UK osprey breeding window.

Thankfully, this didn't turn out to be much of a hindrance. With some Goldilocks weather, Monty never struggled to fish this summer, meaning that his two daughters grew up quickly and strongly. What was most striking about 2013 was the actual speed at which both daughters developed. They both migrated at just 82 days old, the average for Welsh ospreys since 2005 being 102 days.

Record breakers - Both Clarach and Cerist migrate at just 11 weeks and five days old (extreme right, 1R and 2R)

Why did both sisters migrate so early? The chart below shows fledging age (blue) and migration age after fledging (red). There's nothing remarkable in the fledging ages, both sisters got airborne for the first time at 51 days old, just slightly sooner than average. It's the red part of the charts, however, that is telling.

Both sisters migrated just 31 days after taking their first ever flight. Imagine that! Just 4½ weeks after entering the cockpit for the first time, they embark on a 3,000 mile journey to a west African destination they've never been to before. In fact, they most probably haven't been further south than Aberystwyth before.

A big thanks to Heather Corfield for collating these charts

Here's a rather lovely statistic from this year: Two eggs, two girls, hatched two days apart, fledged two days apart, migrated two days apart. Unreal.

But there might be something scientifically significant about 'two' this year. Monty and Glesni only laid two eggs, not three.

Right from the start, Clarach and Cerist were feeding and developing well. They had to. If their development had followed the average for ospreys, they would still be here long into October and be exposed to all the nasty surprises that autumn storms can unleash in the UK. By having just two chicks to feed and nurture this summer and not three, Monty and Glesni have given their two daughters the best start in life. To get both of them on the runway and gone by September 20th is some achievement. It also optimises both Glesni and Monty's genetic investment, both having a 50% stake in each daughter. In an extremely late breeding season, much better to have two 'super-daughters' than three average daughters.

Mother nature ain't stupid. She's been playing this game for a very long time.

And for the Statophiles among us, here are the key dates from this year compared to 2011 and 2012

Here are a couple of videos. The first is of Clarach actually starting her migration last Wednesday and the second of Cerist and Monty starting theirs.

The Dyfi Osprey Project is open for another week, we close Sunday, September 29th so if you're around do pop by and say hello. We might not have any ospreys to show you but we have a load of memories and stories to tell you. We also have some winter visitors on show - these Barnacle geese have just arrived from Greenland. Isn't migration just the most amazing thing?

If you follow the Live Streaming, this will continue until September 30th, but Montgomeryshire Wildlife Trust are pleased to announce that the Live Chat will keep going throughout October!

So what about Monty? He caught 494 fish this year (521 altogether with Glesni's catch. Congratulations to Gail Edgely who won the fish competition!). He entertained half a dozen females in the spring, raised two beautiful and strong daughters, and is now on his own migration south. But when did he go?

This is what I wrote in last week's blog:

"Monty will have two conflicting neurological triggers to juggle right now. The urge to fly south because now is the right time, and the paternal urge to stay and feed his daughters, thereby maximising his genetic investment this year.

There will come a time, probably in September, when the first urge becomes slightly stronger and the scales are tipped in favour of migration and he'll be off. Thing is, no one knows when this time will come yet - not even Monty."

Here's arguably the most amazing statistic of the whole season. Monty stayed and caught fish after fish for his two daughters. Even when the weather turned on him last week, he kept coming back with the goods. He saw his elder daughter go on Wednesday morning and then at 08:36 on Friday morning, his younger daughter also went. He fought off the urge to go himself until he was sure that both Clarach and Cerist had gone.

Just 36 minutes after Cerist went on Friday morning, Monty also started his migration. He knew she had gone. An experienced father now he, like us watching, recognised that familiar circling and ascending, all the time gaining height before that last change in direction and the start of the long flight south at altitude.

Thirty-six minutes was all that Monty needed to make sure that Cerist had gone and make that decision to start his own migration. No need to stay another second, his work on the Dyfi was complete for 2013. What a bird. Wonderbird.

Tan flwyddyn nesa Monty - until next year..