Q.My Corkscrew Hazel Has Lost About 15cms Of 50% Of The Branches Where New Leaves Were Growing – Is This Frost Damage Or Bird/ Squir
rel/ insect damage? The branches look torn and are those with all the new growth in the leaves – it is still looking healthy but very naked of leaves!

Certified GKH Gardening Expert
It could be freeze damage. I wouldn't think squirrels would bother it before the nuts were growing. I'm not clear if only the leaves are lost or the branches look dead. If the branches are dead, cut those out. Hopefully it is not a blight.
These trees get a lot of suckers. Be sure you remove those, as these trees are grafted. Here is more info:
https://www.rhs.org.uk/plants/97648/Corylus-avellana-Contorta/Details
https://www.gardeningknowhow.com/ornamental/trees/contorted-hazelnut/contorted-filbert-tree.htm