Do ospreys recognise their own children?

Here's a remarkable shot taken yesterday afternoon of an intruding osprey landing on Monty's Perch. It's Blue 551 again, one of three brothers from the Clywedog nest in 2020. He's been spotted several times at his ancestral nest too over the last few days.

When these birds return to their natal sites as full-blown adults, are they recognised by their parents as their own offspring?

Short Answer: No

Long Answer: No....

When we've mentioned kin recognition in ospreys in the past we often get accused of wrongly calling the birds 'stupid', or not giving birds enough credit or intelligence, or simply "how do you know..?"

There are many advantages of kin recognition for many animals. For example, the ability to tolerate relatives, to maintain stable family associations of mother and offspring or of sibling juveniles, to reduce kin competition, or to avoid inbreeding.

Charles Darwin never really got to the bottom of the paradox he himself had created within his own laws of Natural Selection: Why would some individuals help others in terms of breeding, feeding and so on. How does this fit into Darwin's "Survival of the fittest" theory?

"The Origin of Species" by Charles Darwin

These altruistic behaviours puzzled him throughout his life.

Natural Selection works on a genetic level (not individual, group, or species level). And the animals he observed helping others were, in most cases, closely related individuals; a sister bee-eater helping another sister feed or care for her young, for example, forgoing her own breeding for that year.

This makes perfect sense, doesn't it? If food or another resource is scarce and passing your genes to another generation via your sibling is better than not at all, this facilitates the evolution of altruistic behaviours in some species.

But this is for smaller birds, usually living in close societies that find advantages in group living.

Ospreys are large birds of prey that usually don't breed until their third of fourth year. Other than inbreeding avoidance, there is no obvious advantage to kin recognition. And how would such a mechanism work anyway? Smaller birds living close together use auditory (bird calls) and olfactory (smell).

How would Telyn recognise Dinas if he landed on her nest later today?

She last saw him in juvenile plumage when she left the Dyfi on 23rd August 2018 when Dinas was 10 weeks old. He's now an adult having gone through several feather moults and is almost four years older.

Aeron returning in 2019 - Monty and Glensi would not 'recognise' him as their own offspring from two years earlier.

Inbreeding pressures are not usually a deleterious factor for ospreys - even in a recovering population as we have in Wales. Rarely do we see close-kin pairings develop and even when it occurs, an osprey's genetic diversity is so large, they can 'afford' the odd close-kin pairing.

Their philopatric behaviour supports this - male ospreys are highly philopatric in various populations around the world (the tendency of an animal to return and breed close to where it was raised). If osprey inbreeding was disadvantageous to productivity, it would be quickly selected out of a population.

So, kin-recognition has not evolved in ospreys and probably most other large birds of prey - the selection pressure to do so is simply not there. But if even if it were, there is probably no biological mechanism that could evolve to enable it.