Putting the Hawk to Flight 139 



older rooks will only permit a few of their last year's off- 

 spring to build near them. If a gentleman has an avenue 

 of fine elm trees in which he desires to have a rookery, 

 but cannot contrive to attract them, though perhaps now 

 and then a nest is partly built and then deserted, an ex- 

 periment founded on this idea might be tried. It would 

 be necessary to ask the assistance of the proprietors of the 

 nearest rookeries, and beg them for one year to refrain 

 from shooting the young rooks, after the well-known 

 custom. An unusual proportion of young birds would 

 then survive, and next building season the larger part of 

 these would return to the old trees and be immediately 

 met in battle by their older relatives. Being driven away 

 from the hereditary group of trees, they would resort to 

 the .next nearest avenue or grove; if they attempted to 

 mix with a strange tribe, they would encounter a still 

 fiercer resistance. In this way possibly the avenue in 

 question might become stocked with rooks. 



One reason, I fancy, why nests begun in such distant 

 trees are so often deserted before completion is that a 

 solitary nest exposes both the building birds and their 

 prospective offspring to grave danger from hawks. No 

 hawk will attempt to approach a rookery the rooks would 

 attack him en masse and easily put him to flight. Chickens 

 are safer under or near a rookery from this cause : a hawk 

 approaching them would alarm the rooks and be beaten 

 away. The comparative safety afforded by numbers is 

 perhaps a reason why many species of birds are gregarious. 

 The apparently defenceless martins and swallows in this 

 way dwell in some amount of security. If a hawk comes 

 near the sand quarry (or the house in the case of swal- 

 lows) they all join together and pursue him, twittering 

 angrily, and as a matter of fact generally succeed in send- 



