that the 70% immature mortality rate is indicative 

 of a declining population. 



Rice (1969) calculated from peregrines trapped 

 for banding on the beaches of the Maryland- 

 Virginia coast that immatures constituted 83% of 

 the population in the 1954-1959 period and 

 84% in the 1960-65 period. The 1954-59 sample 

 included 2 adult males, 37 adult females, 50 im- 

 mature males and 144 immature females. The 

 1960-65 sample included 4 adult males, 26 adult 

 females, 56 immature males and 116 immature 

 females. Cade (1960) estimated 200 to 250 breed- 

 ing pairs in Arctic Alaska. 



Cade (1960) suggests that gyrfalcons can suc- 

 cessfully prevent peregrines from occupying the 

 larger river cliffs and thus affect their density and 

 distribution. 



In the Colville River area of about 36,800 

 km^ on the Arctic slope of Alaska, the popula- 

 tion of peregrines appears to have held rather 

 constant in the number of breeding pairs until 

 about 1970-71, and then started a severe drop. It 

 may now have leveled off at about 30% to 35% of 

 its former numbers, as suggested by data from 1973 

 and 1975. Total numbers of pairs or single adults 

 were as foUows: 1952-1959, 32-36; 1967, 27; 

 1968,32;1969,33; 1971, 25; 1973, 14; 1975, 13. 

 Based on early 1950 studies by Cade, the total 

 population of the Colville drainage may have been 

 between 120 and 160 pairs (White and Cade 1975; 

 Peakalletal. 1976). 



In the Sagavanirktok River area of about 

 2400 km^ on the Arctic Slope of Alaska, the 

 population followed a similar pattern, but appears 

 to have started to decrease earlier and declined 

 slightly more. Total numbers of pairs or single 

 adults were as follows: pre-1950, 11; 1958, 5; 

 1963, 5; 1970, 3; 1972, 2; 1973, 2; 1974,5; 1975, 

 3 (White and Cade 1975). 



Fyfe et al. (1976) note that limited data for 

 other parts of Arctic Alaska indicate a population 

 decline similar to the well-documented decline 

 for the Colville drainage, and that it is doubtful 

 that as many as 50 pairs are still producing young 

 in northern Alaska where Cade (1960) estimated 

 the breeding population at 200 to 300 pairs in the 

 late 1950's. 



In the Canadian Arctic, most populations 

 have dechned to 50% or less of their historically 

 known size. On Ungave Bay, the Interior Barrens, 

 Central Arctic Coast, Banks Island, and the North 

 Slope of Canada where historical records exist. 



only 41% of known nesting sites were occupied in 

 1975. Occupancy of newly found nests declined 

 60% from 20 in 1973 to 8 in 1975, indicating an 

 accelerated decline of Canadian Arctic popula- 

 tions since 1973. 



In western Greenland, the observations of 

 Bumham and Mattox (in Fyfe et al. 1975) re- 

 vealed a substantial density of one peregrine per 

 200 km^ 



REPRODUCTION 



In the Colville River area (36,800 km^) on 

 the Arctic Slope of Alaska, production of young 

 may have started to fall off as early as 1965 or 

 1966. The numbers of young produced in 1952- 

 1959 was 40 to 50; in 1967, 34; in 1968, 34; in 

 1969, 26; in 1971, 14;andin 1973,9 (White and 

 Cade 1975; Peakal et al. 1975). The DDE residue 

 in eggs in that area through 1971 averaged about 

 190 parts per million dry weight (Peakall et al. 

 1975) and egg shells had thinned to about 23% 

 (White and Cade 1975). 



Burnham and Mattox (m Fyfe et al. 1976), in 

 an approximately 1800 km^ area of western 

 Greenland, found a productivity of peregrines 

 averaging nearly 2.5 young per pair over a 4-year 

 period. DDE residues of 332 parts per million 

 found in addled eggs and egg-shell thinning of 

 14% indicate incipient problems for that popula- 

 tion. Eleven peregrine egg shells taken from Arc- 

 tic Ungava in 1967 ranged in thickness between 

 0.25 and 0.33 mm (mean thickness 0.291 mm), 

 representing a 24.4% drop from the 0.385 mean 

 of 30 eggshells measured by Dan Anderson from 

 "eastern Arctic" eggs collected during the first 

 third of the century. In ten eggs checked, DDE 

 ranged from 137 to 498 ppm on a fat basis (D. D. 

 Berger pers. comm. 1970). 



Cade (1960) suggests that when peregrines 

 and gyrfalcons are in direct competition, the gyr- 

 falcon is the dominant competitor. On the Ander- 

 son River, Fyfe (1969) found the gyrfalcon to be 

 dominant and believed that where the two species 

 nest during the same season, the gyrfalcon may 

 displace the peregrine from the better nesting 

 sites such as cliff locations, relegating the peregrine 

 to dirt cutbanks. Natural hazards to nesting are 

 late spring storms or excessive erosion. Because of 

 the short nesting season, renesting is usually not 

 possible (Fyfe 1969). A significant correlation of 

 immature peregrine migration counts along Atlan- 



