Corvids - particularly crows, ravens, and magpies - are notoriously difficult for researchers to track. The birds exhibit something called 'rescue behaviour', in which they see tracking devices as a threat and help each other remove them. Eurasian magpies are the worst, as they not only remove the devices but destroy them, usually by dropping them in bodies of water.
Boru
Boru
‘But it does me no injury for my neighbour to say there are twenty gods or no gods. It neither picks my pocket nor breaks my leg.’ - Thomas Jefferson