Different types of trees are easier to identify at different times of the year.
I will start with those which I find easier to find/identify in spring.
The main feature in spring is catkins on all sorts of trees.
"A catkin or ament is a slim, cylindrical flower cluster, with inconspicuous or no petal". They are fine to leave on the branches and safe to chew on for parrots.
Some trees sometimes have thick green residue on them or even moth, like this on a willow branch:
They can easily be scrubbed off the branches and once the branches are properly washed, they are safe to give to birds.
Willow
Willow catkins are very cute, fluffy things which can be bigger or smaller depending on the species of willow
or this
It is lot harder for me personally to identify some types of willows (weeping willows are always easy to spot though) at any other time of the year, quite frankly, but just to give you an idea - these are young willow trees
Hazel
Again, the hazel is easy to identify by its yellow catkins and it also has quite distinctive dark brown and quite rough bark, even on young branches
It will of course be quite easy to spot Hazel in autumn, one the nuts appear
(Silver) Birch
Silver birches are the easiest to recognise but other birches look quite similar, just for example instead of the really white bark a yellow birch has yellowish/dark brownish bark but of the same rough appearance as Silver birch
Birches also have catkins and later in summer birch nuts, both are edible for parrots
Linden (Lime) Tree
These are quite wide-spread and even though they don't have catkins in early summer they flower in little yellow flowers and later the flowers turn into little pea-shaped fruit. Even though they haven't started flowering of course the last year fruit can still be found hanging on the trees:
This little fruit (as well as the flower to start with) are attached to this little elongated leaf called bract .The rest of the leaves look completely different - they are heart shaped.
Crab Apple
I dont really know how identify apple trees when they dont have apples on! But some crab apple trees might actually still have some apples from last year left on them
Some crab apples are red and some are yellow. Both are fine, and very edible too for the parrots (and humans - I love them all but they do taste quite bitter

)
Ash
Ash is quite widely spread and easy to identify by its sparse and quite dark buds at the moment. The tree bark is greyish and it has quite well define branches with very few smaller twigs.
Ash is going to be easier to identify in summer perhaps as it has quite distinctive leaves (pictures will follow in summer!)
This is all for now, but more will follow as the summer unravels

And this is Lucy, she has helped me to find and take photographs of all the trees and was protecting me from all the wood elves who kept moaning at me for cutting down branches from their trees.
BTW: I am not

, there weren't really any elves, I am not really that crazy, I just really wanted to post the picture of Lucy as she is such a cutie pie in those daffodils