1160 U.S. NATIONAL MUSEUM BULLETIN 237 part 2 



cat account for a few in winter. In summer they are beyond the 

 domain of snakes, cats, most crows, jays, and squirrels, and such com- 

 petitors as English sparrows, starlings, and cowbirds. I found nest 

 mortality and infertile eggs to be 21.3 percent. 



Parasites, both external and internal, were found to be relatively 

 few (Baumgartner, 1937a). Of some 600 specimens carefully in- 

 spected, many were entirely free and none harbored more than a 

 scattering. Of 26 nests observed at Churchill, none showed evidence 

 of infestation. 



The most serious enemies of this species are the elements — snows 

 that cover the food supply, and storms and sudden cold spells, particu- 

 larly during the long migration. While the birds can withstand tem- 

 peratures to —28° C. (West, 1960), they cannot survive without food. 

 A late traveler in the fall, an early one in spring, they run the gantlet 

 of the equinoctial storms at both seasons. W. E. Saunders (1907) 

 counted 358 dead tree sparrows in 3 hours after an October storm on 

 Lake Huron. 



Of the thousands upon thousands of this species that have been 

 handled at banding stations, only a small porportion survive to their 

 4th year. A handful have returned a 5th and 6th year, and the oldest 

 birds on record are a return-8 taken by B. S. Bowdish of Demarest, 

 N.J. (in litt.) and another by Paul Nighswonger (1959) at Alva, 

 Okla. Assuming that these birds were banded in their first winter, 

 they would have been between 8% and 9 years old on last appearance. 



Survival ratio of tree span-ows has been computed by Baumgartner 

 (1937a) based on nest mortality, proportion of first year and adult 

 specimens collected through the season, and banding returns, both 

 personal and those recorded in the literature. 



Calculating the fate of a potential 750 eggs from 150 nests: 



78.7 percent survive the nestling period =590 birds 

 50 percent of these 590 survive the 



first migration and winter =295 birds 



40 percent of these 295 make winter Rl =119 birds 



43 percent of these 119 survive to R2 = 51 birds 



34 percent of these 51 survive to E,3 =18 birds 



28 percent of these 18 survive to R4 = 5 birds 



16 percent of these 5 survive to R5 = 1 or 2 



birds 



By the sixth summer only one old veteran remains, who may live 

 one or two more years. 



Fall and tuinter. — Beginning the southward trek in September, the 

 hordes of tree sparrows reach southern Ontario about the first of 

 October (Taverner and Sutton 1934) and by the end of the month are 



