Birds offer in some respects better evidence than quadrupeds, from their breeding more rapidly and being kept in greater numbers. We have seen that carnivorous animals are more fertile under confinement than most other mammals. The reverse holds good with carnivorous birds. It is said[350] that as many as eighteen species have been used in Europe for hawking, and several others in Persia and India;[351] they have been kept in their native country in the finest condition, and have been flown during six, eight, or nine years;[352] yet there is no record of their having ever produced young. As these birds were formerly caught whilst young, at great expense, being imported from Iceland, Norway, and Sweden, there can {154} be little doubt that, if possible, they would have been propagated. In the Jardin des Plantes, no bird of prey has been known to couple.[353] No hawk, vulture, or owl has ever produced fertile eggs in the Zoological Gardens, or in the old Surrey Gardens, with the exception, in the former place on one occasion, of a condor and a kite (_Milvus niger_). Yet several species, namely, the _Aquila fusca_, _Haliaetus leucocephalus_, _Falco tinnunculus_, _F. subbuteo_, and _Buteo vulgaris_, have been seen to couple in the Zoological Gardens. Mr. Morris[354] mentions as a unique fact that a kestrel (_Falco tinnunculus_) bred in an aviary. The one kind of owl which has been known to couple in the Zoological Gardens was the Eagle Owl (_Bubo maximus_); and this species shows a special inclination to breed in captivity; for a pair at Arundel Castle, kept more nearly in a state of nature "than ever fell to the lot of an animal deprived of its liberty,"[355] actually reared their young. Mr. Gurney has given another instance of this same owl breeding in confinement; and he records the case of a second species of owl, the _Strix passerina_, breeding in captivity.[356]