HISTORICAL AND EXPERIMENTAL STUDY OF HOMING. 41 



the night upon the water in the absence of drift-wood accounted for the 

 failure of many of the birds to return to Bird Key. The 1913 experiments 

 upon homing between Galveston and Bird Key (p. 54) seem to show that 

 entire reliance can not be placed upon the results of the experiments we have 

 just considered. In the Galveston tests many of the birds were out upon the 

 water (apparently) during periods ranging from 5 nights to 17 nights. Hence 

 we must conclude either that drift-wood was abundant or else that the sooty 

 when not confined can spend the night upon the water. If our results are 

 taken at their face value they would seem to force the conclusion that the 

 Galveston sooties were able to find something to rest upon during the night. 



RETENTION OF NESTING HABITS. 



In controlling experiments upon homing it becomes essential to know (1) 

 the length of time the bird left on the nest (O) will care for the nest, egg, young, 

 etc., and (2) the length of time nest habits will be retained by the bird which 

 has been sent away (R). The necessity for data on (1) arises by reason of 

 the fact that as soon as the bird left at home begins to desert the nest, other 

 birds steal the straws, if it is a noddy nest, or fill it with sand, disarrange the 

 egg, etc., if it is a sooty nest. Nests so disturbed will not be taken by birds 

 returning from the experiments on homing. Since the observer can not keep 

 all of the nests under observation at any one time, it is essential that they be 

 kept in good condition by the bird remaining at the nest. In order to control 

 this factor perfectly it would be advisable in future experimentation to invert 

 wire cr j;es (with open doors) over the nests several days before capturing the 

 birds \\ hich are to be sent from the island. These nests could be watched and 

 as soon as the O at any given nest begins to desert, the door of the cage could 

 be closed up until R was expected. R having been habituated to the cage before 

 he left, would not hesitate to enter it on his return if the door were left 

 open or to perch upon it if the door were closed. 



The necessity for data on (2) appears when we consider the possibility of the 

 effect of loss through disuse (or waning) of nest habits, upon the possibility 

 of locating the bird (R) upon its return. If nest habits, habits formed to a 

 particular nest, to mate, etc., are lost at the end of 2 or even 3 weeks, it is 

 unlikely that the total number of birds returning from long trips can ever be 

 observed. Fairly complete data have been gathered upon (1). 



OBSERVATION UPON BEHAVIOR OF BIRD LEFT AT NEST (o) AFTER REMOVAL OF 



NEST MATE (R). 



So many observations have been made upon this phase of the subject, that 

 only a small number of our records will be given. We present in table 4 

 the behavior of 24 birds whose mates had been sent to Galveston. The mates 

 were removed May 15, 1913. During the first 6 days the O's carefully guarded 

 the nests, usually sitting closely upon the eggs. Occasionally short trips for 

 food and water were made. This, in the case of the sooties, means a tremen- 

 dous change in habits, since they ordinarily leave the nest for 24 hours at the 

 nest shift. 



Records similar to the above were kept upon several different occasions, 

 but the results were identical. Summarizing (1), we find that both noddies 

 and sooties, when left alone at the nest, remain on guard and brood the egg 



