by 17 pairs (94%) in 1966 but by no more than 3 

 pairs and a single bird in 1973 (22% occupancy). 

 In northern Alberta, 12 eyries were occupied by 6 

 pairs in 1971, but in 1973, by only 4 pairs and 2 

 single birds. In an overall 1973 Canadian survey 

 of 83 eyries rechecked, 49 occupied by 44 pairs 

 (Fyfe in Clement ed 1974). 



In western North America, there were formerly 

 densities of slightly more than 1 pair per 5,180 

 km^ in areas where the bird was considered 

 "common;" in mountains and arid regions, where 

 it was considered "rare," density was estimated as 



1 pair per 51,800 km^ (Bond 1946). In the 

 Rocky Mountain region, of 28 or 29 peregrine 

 eyries active in 1938, not more than 4 to 6 were 

 found occupied later. An estimated 80% to 90% 

 of older sites in Utah, Idaho, Oregon, western 

 Wyoming and western Montana have been deserted 

 and the population shifted north or to higher 

 elevations to compensate for drought conditions 

 in recent times (Nelson 1969). In 1964, only 

 slightly more than 33% of known peregrine nest 

 sites in the Rocky Mountain region of New 

 Mexico and Colorado were being used. Many sites 

 were not used after 1950. An estimated 25 pairs 

 currently nest in Colorado and Wyoming, approx- 

 imately 25 pairs in Arizona, New Mexico and 

 Texas, nearly 25 pairs in Montana and possibly 60 

 pairs in Alberta (Enderson 1969a). Enderson 

 (1977) found that the population in the Rocky 

 Mountains region had changed little over the last 



2 years. Egg production was typical for the species 

 but only half of the eggs were deemed hatchable. 

 About 40 eyries in Utah are active at one time or 

 another. Based on their density, if all eyries were 

 active at once there would be about 5,499 km^ 

 per eyrie. If 11 suspected but unverified eyries 

 were excluded, density would be 1 eyrie for every 



7.6 km^. 



Peregrines are much more common around 



the Great Salt Lake than in other parts of Utah. 

 Density appears to be directly related to avail- 

 ability of food and suitable nesting cliffs. Average 

 distance between 13 eyries along 209 km of the 

 west face of the Wasatch Mountains is 16.1 km. 

 The closest spacing was about 3.2 km apart (Por- 

 ter and White 1973). 



In the Rocky Mountains region in general, 

 data indicate a 50% population decHne (Enderson 

 in Clement ed 1974). Annual natural mortality 

 there ranges from 20% to 25% for aduhs and 50% 

 to 55% for juveniles (Rocky Mountain/Southwest 



Peregrine Falcon Recovery Team 1977). Approxi- 

 mately 100 pairs were reproducing successfully in 

 California in 1946; the decline began in the early 

 1950's. In 1970, 10 birds were present at 4 sites. 

 The California population is probably reduced at 

 least 50% from 25 years ago. Evidence indicates 

 that the total number of successful pairs in Cali- 

 fornia in 1970 did not exceed 5 (Herman 1971; 

 Herman etal. 1970). 



Banks (1969) found evidence of a decline in 

 Baja Cahfornia and the Gulf of California, with 

 indication of lowered productivity in the latter 

 area in the 1960's. Anderson (1976) found no 

 peregrines on the west coast of Baja, California 

 between 1971 and 1975. He estimated 35 to 50 

 active nests in 30 to 35 local areas along the Gulf 

 of California and 75% of them occupied over a 5- 

 year period. Of 6 known successful nestings, 

 there were 2.2 young per nest. Thus it was as- 

 sumed that pesticide pollution was not too acute 

 at that time. Porter and Jenkins (1977) also 

 found no nests occupied on the west coast of 

 Baja, California, and the population along the 

 Gulf of Cahfornia much the same as former years. 



Farther east in the northern Mexican high 

 country, three eyries on the western slope of a 

 single 3,000 m ridge of the Sierra Madre Occiden- 

 tal were separated by distances of 5 and 21 km. 

 In the Sierra Madre Oriental 6 pairs were found in 

 an 18.2-km circle, with the average distances 

 separating 6 eyries 5.2 km. Of 19 pairs present in 

 the Chihuahuan Desert region of northern Mexico 

 in 1976, 13 (68%) produced young, indicating a 

 moderately healthy population (Hunt 1976). To- 

 day, the mainland population in Mexico may ex- 

 ceed 100 pairs, while in Baja, California there 

 may be an additional 50 pairs, although only 

 about 20 to 30 are currently known (R. D. Porter, 

 W. G. Hunt in King in press). 



REPRODUCTION 



In Massachusetts, peregrines occupied breed- 

 ing stations before the end of February, and laid 

 the first eggs by 25 March. The female chose and 

 prepared the nest hollow on a cliff ledge. At least 

 one day elapsed between the first, second, and 

 third eggs, and sometimes 2 days between the 

 third and fourth egg (Joseph Hagar in Bent 1938). 

 A clutch ordinarily included 3 or 4 eggs, oc- 

 casionally 5, and very rarely 6 or 7. Regional 

 gradients in clutch size were reported by Hickey 

 (1942) and Bond (1946). 



