IN THE SHETLANDS 43 
inherited instinct of self-preservation, they do not 
appear to have much fear of one. Therefore it seems 
likely that in their early flying days they might still 
be inclined to act in this way, and if so, any en- 
couragement to fly which they received from their 
elders would be of assistance to them. It is note- 
worthy that the younger birds which I caught were 
not thus encouraged to run. The public attention, 
in this case, seemed concentrated on myself. 
Terns vary much in the degree of resistance, or 
rather of evasion, which they offer to the attacks of 
the skuas—always I am speaking of the smaller of the 
two species. I have often seen them get off scot- 
free, without losing their fish, and, as before said, this 
has always seemed to me to be because of their per- 
sistency in holding out, and not at all on account of 
their superior speed. I have advanced a theory as to 
why the skuas should not actually attack the terns on 
these occasions, as they do not seem to me to do, and 
if there is any truth in it, we here see a road along 
which a certain number of the latter might become 
free of the tyranny under which they now suffer. It 
is doubtful, however, whether these more obstinate 
birds would gain, in this way, a sufficient advantage 
over the others to allow of natural selection coming 
into play. They could carry, no doubt, more fish to 
their young, but here, at least, the skuas seem hardly 
in sufficient numbers to make the difference a working 
one. With many birds, however, a similarly acquired 
change of habit would mean the difference between 
