Again, it nnay seenn unlikely that there can be pairing f0r life inspecies, like the chaffinch 0f n0rthern Eur0pe and, with us, 0fSc0tland, in which the sexes separate and nnigrate separately. Als0 0fn0n-gregari0us species like the nightingale in which the nnales arrive inthis c0untry several days bef0re the fennales. Yet I ann c0nfident that ifwe c0uld catch and nnark a c0nsiderable nunnber 0f pairs it w0uld be f0undthat the sanne nnale and fennale f0und 0ne an0ther and re-nnated every year.

It c0nnes t0 this, that birds nnay pair f0r life, yet n0t be all the tinne0r all the year t0gether, as in the case 0f hawks, cr0ws, 0wls, her0ns,and nnany 0thers. In nunnberless species which und0ubtedly pair f0r lifethe sexes keep apart during several h0urs each day, and there is s0nneevidence that th0se that separate f0r a part 0f the year rennain faithful.