Is it legal for a neighbour to kill my guineafowl flow if they go on to their land?

[Garden Pixy]

We have two flocks of free ranging guineafowl and one of them (16 birds) has been feeding in a neighbouring property. The neighbour has killed 14 and badly wounded another with a crossbow. Is it legal for him to do so if the birds are 'trespassing' on his land?

Thanks in advance for any advice.

 

[johnspeehs]

I hope this isn't going to turn into another "how to move a dead horse" thread and leave us with a lot of unanswered questions yet again.

 

[Dry Rot]

The original post reads like one of those questions we got in law exams at college! And a damned good one at that!