Montgomeryshire Wildlife Trust are honoured this week. This website is exactly two years old this month and to celebrate, we have for the first time, a guest writer.

This blog is written by none other than Paul Wildlifewriter.

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Glesni was last seen at Cors Dyfi on 31st August just after 08:00 BST. This is the final nest camera image recorded of her for this season.

Glesni has started her migration even though the fledglings are still not ready to undertake theirs. This may seem like a reckless and uncaring abandonment, but in fact some of the reasons for her departure have the youngsters' own future as a basis. The first and most important point to understand is that it was never in Glesni's “job description” to wait until they were ready to go...

Once the chicks had fledged, her work for the season was effectively complete. She had incubated them, brooded them, fed them and protected them for a hundred (and one) days but, once they could fly, there was no need for the same standard of care. The only practical tasks left are the provision of more food and the defence of the nest site from other ospreys – and in truth, both of these are Monty's department.

In evolutionary terms, the balance of the numbers dictates that Glesni – and other osprey females – should take their leave at this stage. If they were to remain, they would be doing little more than competing with their own offspring for resources – not perhaps a problem on the super-productive Dyfi estuary, but a bad situation in other locations where those resources might be becoming scarcer towards the end of the season.

Many other species of birds face this same quandary: the young of migratory shorebirds and waders, who can usually fend for themselves soon after hatching (“precocial nesters”), are often deserted by both parents and any non-breeding adults, leaving the maximum available food supply to the next generation.

Monty will now be the sole provider of food for his two daughters until he deems them ready to fend for themselves

This is the behavioural tension that Glesni has been feeling over recent days: maternal inclination vs evolved instinct – and the latter will always prevail sooner or later. The earlier she can start her journey south, the better: in 2013, Glesni is no longer the footloose floosie from Rutland Water, wandering the landscape and stirring up trouble at other nests. Now, she is a breeding female herself, with high status in osprey “society”: a matriarch-in-the-making for future generations. She needs to get back to her chosen wintering grounds where she will occupy the feeding spots of choice, by right. And now is the time...

This chart shows that the north Atlantic jetstream, after flopping about over the British Isles for almost the entire Spring and Summer, has swung north at last.

This change means that migration condition were favourable on Saturday and Sunday, with following winds for our south-bound birds right down through France and Spain to edge of the Sahara itself. Glesni can take full advantage by going while the going is good.

And why not? Nesting for the first time this season, she has learned quickly “on the job” and it has paid off: her chicks got the best start in life that she could provide for them, and she may even have laid the foundations for a dynasty of ospreys to come.

We don't know where Glesni spends the winter months, of course, but I like the idea of her finally relaxing on some far west African shore as the sun goes down. She has surely earned it.

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A huge thank you to Paul for writing this blog about Gesni's departure and for sharing his knowledge with us all.

Here's a video of Glesni leaving her Dyfi nest(s) for the last time in 2013