The signal of danger among Birds seems to be of universal comprehension; because the instant it is uttered we hear the whole flock, though composed of various species, repeat a separate moan, and away they all scuttle into the bushes for safety. The sentinel Birds give the signal, but in some cases they are deceived by false appearances. Dr. Edmonstone, in his "View of the Zetland Isles," relates a very striking illustration of the neglect of the sentinel, in his remarks on the Shag. "Great numbers of this species of the Cormorant are sometimes taken during the night, while asleep on the rocks of easy access; but before they commit themselves to sleep, one or two of the number are appointed to watch. Until these sentinels are secured, it is impossible to make a successful impression on the whole body; to surprise them is, therefore, the first object. With this view, the leader of the expedition creeps cautiously and imperceptibly along the rock, until he gets within a short distance of the watch. He then dips a worsted glove into the sea, and gently throws water in the face of the guard. The unsuspecting Bird, either disliking the impression, or fancying, from what he considers to be a disagreeable state of the weather, that all is quiet and safe, puts his head under his wing and soon falls asleep. His neck is then immediately broken, and the party dispatch as many as they choose." Addison was a true lover of nature, which he shows in two letters written by him to the Earl of Warwick (afterwards his son-in-law), when that nobleman was very young. "My dear Lord," he writes, "I have employed the whole neighbourhood in looking after Birds'-nests, and not altogether without success. My man found one last night, but it proved a hen's, with fifteen eggs in it, covered with an old broody Duck, which may satisfy your Lordship's curiosity a little; though I am afraid the eggs will be of little use to us. This morning I have news brought me of a nest that has abundance of little eggs, streaked with red and blue veins, that, by the description they give me, must make a very beautiful figure in a string. My neighbours are very much divided in their opinions upon them: some say they are a Skylark's; others will have them to be a Canary-Bird's; but I am much mistaken in the colour and turn of the eggs if they are not full of Tomtit's." Again, Addison writes:--"Since I am so near your Lordship, methinks, after having passed the day amid more severe studies, you may often take a trip hither and relax yourself with these little curiosities of nature. I assure you no less a man than Cicero commends the two great friends of his age, Scipio and Lælius, for entertaining themselves at their country-house, which stood on the sea-shore, with picking up cockle-shells, and looking after Birds'-nests."