248 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1936 



For the most part, nevertheless, heavy winter predation upon bob- 

 whites by horned owls signifies a crowded condition of the quail 

 population, although in terms of numbers there need not necessarily 

 be many quail present in a given area to over-populate it. Much 

 "quail country" is inferior in quality as it exists at present and can 

 accommodate but a very limited population, often a population far 

 lower than that which the public may think ought to be there. 



It should be recognized that a population of 10 birds in an environ- 

 ment having a carrying capacity of 5 per square mile is crowded 

 just as truly as is a population of 300 in environment having a carry- 

 ing capacity of 150 per square mile. Less conspicuous mortality 

 will be suffered by the smaller population, but the position of the 

 5 extra birds seems to be about as insecure as the position of the 

 150 extra ones ; where populations exceed the capacity for accommo- 

 dation set by the environment as it stands, the precarious position of 

 the excess birds simply invites predation. 



Much quail environment is overpopulated by autumn as a natural 

 consequence of the season's increase of young birds and the annual 

 change from fall to winter conditions of vegetation. Further 

 shrinkage of carrying capacity may follow the clearing away of 

 brush or the burning of vegetation by farmers; fall plowing; clean 

 harvesting ; close grazing, etc. ; or emergencies that may evict popu- 

 lations or parts of populations from environments that otherwise 

 would have accommodated them. Deep snows, in particular, by 

 covering up the food in many parts of an area, may cause concen- 

 tration of birds in other places where food may still be had. 



On that part of area A, table 1, where most of the 1934-35 preda- 

 tion of horned owls upon quail took place — 8 of 42 pellets containing 

 quail remains — ^hungry quail kept drifting in from the outside 

 throughout the winter. 



This tract of land had a carrying capacity of around 53 bob- 

 whites, as calculated on the basis of the numbers that had successfully 

 wintered there in previous nonemergency years. As nearly as the 

 1934—35 story could be pieced together from almost continual field 

 studies, 72 quail started the winter and 50 were surviving by spring; 

 but in the meantime there had been much movement in, some move- 

 ment out, and a mortality that could be fairly closely determined at 

 54 birds, or a loss exceeding the number that wintered. 



As long as the quail occupying this tract filled it up only to the 

 limit of its known carrying capacity, the population suffered negli- 

 gible losses from predation, from horned owls as well as from other 

 resident predators. But whenever the environment became filled 

 with quail past carrying capacity, the surplus birds soon departed 

 (or their equivalent number did), or increased pressure from enemies 

 cut the population down to the level of carrying capacity again. 



