Sketches of Spanish Bird-Life 401 
quoted was at first at fault. For the great spotted cuckoo differs 
in one essential point from that ‘‘ wandering voice” with which we 
are familiar at home. The latter deposits a single egg in casual 
nest of titlark, hedge-sparrow, wagtail—in short, of any small bird, 
regardless of the fact that its own egg may differ conspicuously 
from those of its selected foster-parent. The spotted cuckoo is 
more circumspect. Everywhere it restricts the delegated duty to 
some member of the Corvidae,' and in Spain exclusively to the 
magpies. Moreover, whether by accident or evolution, the cuckoo 
has so admirably adapted the coloration of its own egg to resemble 
‘that of its victim, as to deceive even so cute a bird as the magpie. 
Earlier ornithologists (as above suggested) failed for a moment to 
distinguish the difference—it was, in fact, the zygodactylic foot 
of an unhatched embryo that first betrayed the secret (Tristram, 
Ibis, 1859). On close examination the cuckoo’s eggs differ in their 
more elliptic form and granular surface; but, unless previously fore- 
warned and specially alert, no one would suspect that these were 
not magpies’ eggs, any more than does the magpie itself. 
The spotted cuckoo deposits two, three, and even four eggs in 
the same magpie’s nest, sometimes leaving the lawful owner's eggs 
undisturbed, in other cases removing all or part of them—we have 
noticed spilt yoke at the entrance. It would appear difficult, in 
these domed nests, for the young cuckoos to eject their pseudo- 
brothers and sisters; but this detail of their life-history remains, 
as yet, unsolved. 
Crosspitts.—Nature delights in presenting phenomena which 
no tangible cause appears to warrant. Such were the thrice- 
repeated invasions of Europe by “Tartar hordes”—they were 
only sand-grouse—that occurred during the past century (in 
1863, 1872, and 1888); and in 1909 an analogous problem, 
though on minor scale, was offered by crossbills. From north 
to extreme south of our Continent these small forest-dwellers 
precipitated themselves bodily westwards. This was in July. 
All the west- European countries, from Norway to Spain, 
recorded an unwonted irruption, In Andalucia (at Jerez) 
crossbills were first noticed about mid-July, and their appearance 
so impressed country-folk little accustomed to discriminate small 
birds, as to suggest to them the idea that the strangers must 
1 In Egypt the hooded crow (Corvus cornia) is invariably the cuckoo’s dupe ; in Algeria, 
Pica mauretanica. 2 
D 
