BIRD ADAPTATIONS 



interesting for me to see this migratory fat still preserved by birds 

 at the time of their arrival on the nesting ground, and then diminish- 

 ing markedly during the period of courtship of the male and some- 

 where along during the incubating period of the female. So I am not 

 sure that it is strictly and seasonally a migratory fat, although it 

 may beusefulforthebird topackhis California fat up to Alaska. But 

 certainly the moment when migratory fat is utilized is, like the fat 

 of the bull fur seal, during the actual breeding period. 



WEST: Are you speaking of shore birds primarily? 



IRVING: It is pretty general among the birds arriving in arctic 

 Alaska breeding grounds. There are some 40 species for which I 

 have sufficient records to be indicative including all families and 

 sizes. 



WEST: Do you think possibly a sandpiper or plover who may 

 fly non-stop over a great distance could retain a large proportion 

 of his fat when he reaches the breeding ground? 



IRVING: They do have considerable fat when they arrive so far 

 as I can compareweights with those of similar birds when they were 

 ready to depart from the wintering grounds. They may be a little 

 less fat, but they are still very fat birds. 



WEST: The question then arises how they get enough energy to 

 fly that distance unless they stop enroute to keep augmenting their 

 fat stores, which we know to be the case in passerines. 



IRVING: I realize these are net results, but the situation of the 

 observer can change one's point of view. You mentioned the energy 

 requisite for reproduction. The other day I was looking at the eggs 

 of Least Sandpipers, which, like all sandpipers, are quite large. We 

 weighed these and the four eggs weighed 25 grams. They were laid 

 on four successive days and the female bird which produced them 

 weighed 21 grams; I suggest that you might start introduction of 

 Least Sandpiper blood into white leghorns because the sandpiper 

 equals her weight in egg production in four days, instead of the two 

 months necessary for the good white leghorn to equal her weight of 

 egg production. 



325 



