80 



NORTH AMERICAN FAUNA 73 



Ring-billed Gull [Lams delawarensis) 

 Status: Regular migrant. 



Migration: Abundant spring and fall migrant throughout the Valley. Spring 

 migrants return 10-20 March. Peak abundance occurs between 15 April and 

 1 May and departure by 20 May. Fall migrants arrive in early September 

 (earliest— 24 August 1961, Burnett County). Peak abundance occurs be- 

 tween 15 September and 1 October. Flocks totaling 200 individuals are 

 common during this period, and flocks of 500 are regularly observed. Fall mi- 

 grants depart by 10 November (latest— 17 November 1965, St. Croix 

 County and 26 November 1976, Washington County). 



Habitat: Ring-billed gulls use a variety of wetland types during migration 

 including semipermanently and permanently flooded wetlands, large lakes, 

 and the St. Croix River. During fall migration, ring-billed gulls make exten- 

 sive use of recently plowed agricultural fields. 



Franklin's Gull (Larus pipixcan) 

 Status: Regular migrant. 



Migration: Rare migrant in the Western Upland and at Crex Meadows, Bur- 

 nett County; absent from the forested regions. Spring migrants arrive be- 

 tween 25 April and 1 May (earUest— 13 April 1954, Burnett County) and de- 

 parture occurs by 25 May. Fall migrants arrive 20-25 September. Peak 

 abundance occurs 1-20 October and departure by 10 November. During 

 peak fall migration. Franklin's gulls are commonly found in association with 

 ring-billed gulls on freshly plowed agricultural fields in western St. Croix 

 County. Flocks of 200 to 300 are not uncommon and during the mid- 1 960 's, 

 S. D. Robbins occasionally found flocks of 1,500 FrankUn's gulls in mid- 

 October. Migrants follow a rather narrow migration path through the 

 Western Upland; the major route is associated with the area of Prairie Wet- 

 lands. FrankUn's gull is virtually absent east of R. 17 W. in St. Croix and 

 Polk counties. 



Habitat: Largely restricted to semipermanently and permanently flooded 

 wetlands. Extensive use is made of agricultural fields during fall migration. 



Bonaparte's Gull {Larus Philadelphia) 

 Status: Regular migrant. 



Migration: Uncommon migrant throughout the Valley, fairly common on the 

 prairie wetlands of St. Croix and Washington counties. Spring migrants 

 return between 25 April and 1 May (earUest— 12 April 1971, Washington 

 County). Peak abundance occurs 10-15 May and departure by 25 May. Fall 

 migrants arrive about 10 September. Peak abundance occurs 20 September 

 to 1 October and birds depart by 25 October. During the fall, Bonaparte's 

 gulls are most commonly found along the St. Croix River, becoming rare to 

 absent elsewhere. 



