The bird nest mystery?

Back in October when we started (and we will finish!!) taking down the leylandii trees we came across several old birds nests located in the dense foliage at the tops of the trees. One of them contained two eggs --

How long they had been there or what they were we had no idea. We did wonder at the time if because there were two different, one could be a cuckoo.

The smaller of the two we best guessed to be that of the Nuthatch ....

Nuthatch eggs

As for the second egg, our internet research determined that cuckoo eggs become more like the hosts eggs both in colour and markings and that certain features of the host bird eggs, such as shape, colour and markings undergo specific changes during cuckoo parasitism to help the bird distinguish them from those of the cuckoo’s.  The phenomenon is called egg mimicry. There is no sign of this in the nest we found.

Could it be that the nest has been used twice? We are not ornithological experts and never likely to be so. If you can solve this mystery or have any other thoughts please leave your comments. In the meantime it remains unsolved.