Half an hour later we descried the unmistakable eyrie of an imperial eagle--a platform of sticks that crowned the summit of a huge cork-oak, the more conspicuous since any projecting twigs that might interrupt the view are always broken off. The eagle, entirely black with white shoulders, only soared aloft when L. was already half-way up. The two handsome eggs we left, though they have since, presumably, added two more "detrimentals" to prey on our partridges. Eagles, so soon as adult, pair for life; but that condition may require several years for full attainment, and in the imperial eagle the adolescent period is passed in a distinctive uniform of rich chestnut. So long ago as 1883, however, we discovered the singular fact that this species breeds while yet (apparently) "immature." That is, we have frequently found one of a nesting pair in the paler plumage described, while its mate gloried in the rich sable-black of maturity, as sketched on p. 31. This year (1910) we had come across such a couple--they had two eggs on March 15--the male being black, while his partner was parti-coloured. A curious incident had occurred at that nest; at dawn next morning a griffon vulture was discovered asleep close alongside the sitting eagle. But on the arrival of the husband a furious scene ensued! The intruder (whom we acquit of dishonourable intent) was set upon, hustled, and violently ejected from the tree--hurriedly and dishevelled he departed. But conjugal peace was soon restored, and presently the royal pair set out in company for a morning's hunting. These resident birds-of-prey breed early. We have found the eagles' eggs by February 28, buzzards' on March 12, and red kites' on March 14. This spring was remarkable for the numbers of hobbies that passed north during May, sometimes in regular flocks. They often roosted in old kites' nests, and when disturbed therefrom misled us into a futile climb. * * * * * WHITE-TAILED OR SEA-EAGLE (_Haliaëtos albicilla_).--This does not properly belong to the Spanish zone. We cannot find recorded a single authentic instance of its occurrence in that country, but can supply one ourselves. In the early days of February 1898 we watched on several occasions an eagle (which at the time we took to be Bonelli's) wildly chasing the geese that are wont to assemble in front of our shooting-lodge. Splendid spectacles these aerial hunts afforded. The selected goose, skilfully separated from his company, made a grand defence. Fast he flew and far, now low on water, now soaring upwards in widening circle; but all the time gaggling and protesting against the outrage in strident tones that we could hear a mile away. Never, so far as eyesight could reach, did the assailant make good his hold.