692 U.S. NATIONAL MUSEUM BULLETIN 237 part 2 



attract and kill varying numbers of nocturnal migrants, Savannahs 

 included. 



But the greatest menace to migrants has resulted from two fairly 

 recent innovations: the television tower and the airport ceilometer. 

 Both these instruments have taken a fantastic toll of migrants; for 

 example, 50,000 birds were killed during one October night at a 

 ceilometer in Georgia (Johnston, 1955). Stoddard (1962) reports 

 15,000 birds killed at a Florida TV tower in 6 years; the Savannah 

 sparrow is nearly always represented in these mass kills. 



Winter. — The southeastern United States forms the major winter- 

 ing ground for not only the eastern races (oblitus, labradorius, savanna), 

 but for at least part of the population of the more western nevadensis. 

 Here the races intermingle without apparent habitat or social segrega- 

 tion (Johnston, 1956; Norris and Hight, 1957; Quay, 1957; Norris, 

 1960). 



As noted earlier, the Savannah sparrow becomes common in South 

 Carolina (Savannah River Plant) by November, and remains abun- 

 dant throughout the winter. The population gradually builds up to 

 a December peak, which then drops until it becomes stabilized dming 

 February and March (Non-is and Hight, 1957). During this period 

 the total population fluctuates to some extent, but Norris (1960) 

 estimates that on the average there are about four or five bhds per 

 acre, and more — up to 30 per acre — in particularly favorable fields. 

 Odum and Hight's (1957) estimate of the same population in the 

 same area with a different census technique showed about 10 birds 

 per acre. This represents no real discrepancy for even the short- 

 term home range of a Savannah sparrow is about 8 acres, and Norris 

 (1960) found evidence that some birds exhibited even greater vagility 

 over an extended period. 



If the post-December drop in the numbers of Savannah sparrows 

 at the Savannah River Plant occurs annually, it suggests the presence 

 in the December population of birds who have not yet reached their 

 usual winter quarters farther south. If this drop occurs only sporad- 

 ically, it may be a "hard weather" movement, such as Quay (1957) 

 noted in North Carolina: 



The month from January 14 to February 14, 1948, was a time of continuously 

 below-normal temperatures and repeated sleetfalls, snowfalls, and ice glazes. 

 * * * During January 14-23 there were daily freezing temperatures, frequently 

 down to 10-15 degrees Fahrenheit. This sharp drop in temperature alone caused 

 no visible change in the savannah sparrow population. On the 24th of January 

 two inches of snow and fine sleet fell, accompanied by a glaze of ice on the vege- 

 tation. The sleet and snow covered the bare ground completely through the 

 26th, and thirty per cent of the ground still by the 30th. The ice glaze melted 

 by the afternoon of the 25th. 



The savannah sparrows were entirely gone on the 25th from all the Tall Weeds 

 and Andropogon Plots, from all the Digitaria-Medicago Plots except for 24 birds 



