1874.] MOLOTI1RI OF BUENOS AYRES. 1/1 



The Patagonian Thrush (Turdus falklandicus) is not a singing 

 bird ; occasionally, however, in spring, an individual is heard to sing. 

 I believe the singing in this case is a recurrence to a disused habit, 

 because most Thrushes sing, also because the La-Platan Thrushes never 

 sing in winter or during high winds in summer (high winds prevail 

 all summer in Patagonia, though the winter is calm), also because 

 the song of T. falklandicus, when it does sing, is like a laboured 

 imitation of the song of T. rvfiventris of La Plata, the species which 

 it most closely resembles. 



The following also appears to be an example of recurrence to an 

 ancestral instinct. A physiological study of the Ophidians has, I be- 

 lieve, afforded some reasons for supposing that these reptiles or their 

 progenitors were all originally aquatic in their habits. The extreme 

 readiness with which land-snakes enter the water, their apparent 

 fondness for it, as if it were their native element, and the facility with 

 which they swim give greater strength to the supposition. Last 

 summer (December 1872) I noticed a Coronella anomala on the 

 border of a stream where I was fishing, with its body so much dis- 

 tended that, curious to learn what it had swallowed, I killed and 

 opened it. There were in it fifteen little fishes, varying in size from 2 

 to 3^ inches in length. A few of the fishes had begun to decompose ; 

 but they had evidently all been taken that day, showing in what 

 marvellous perfection this individual possessed the fishing instinct. 

 Yet the G. anomala (our commonest snake, though until lately un- 

 described) abounds everywhere on dry elevated plains where there is 

 never any standing water. This snake was a full-grown male 14^ 

 inches long ; the female differs in colour, and is much larger. From 

 the number of leaves that had been swallowed along with the fishes 

 it was evident that the snake had lain among the rotting leaves of the 

 floating water-lilies to watch for its prey ; and indeed the colour of 

 the body, the stem-like raised neck, and still watchful habit seem to 

 adapt it for preying on fish in the water rather than on mice, birds, 

 &c. on dry land. 



The last case of recurrence, or what appears such, will pro- 

 bably seem less obvious than the preceding ones ; it refers to Molo- 

 thrus bonariensis, and a strange purposeless habit of that species 

 already mentioned in a former paper. Before and during the breed- 

 ing-season the females, sometimes accompanied by the males, are seen 

 continually haunting and examining the domed nests of some of the 

 Dendrocolaptidse. This does not seem like a mere freak of curiosity, 

 but their persistence in the habit is precisely like that of birds that 

 habitually make choice of such breeding-places. It is most surpri- 

 sing that they never do in reality lay in such nests, except when the 

 side or dome has been accidentally broken enough to admit the light 

 into the interior. Whenever I set up boxes in my trees, the first 

 bird to visit them is the female M. bonariensis. Sometimes one 

 will spend half a day loitering about and inspecting a box, repeatedly 

 climbing round and over it, and always ending at the entrance, 

 into which she peers curiously and, when about to enter, starting 

 back as if scared at the obscurity within. But after retiring a 



12* 



