BIRDS OF BOULDER COUNTY, COLORADO 1 83 



at tne present time be expected to occur, either commonly or rarely. 

 In a few cases records from the adjoining regions have influenced the 

 expectations. 



The term permanent resident has been applied to those species of 

 which some individuals are present regularly at all times; summer 

 resident, to those which presumably nest in the region but are not 

 present in winter; winter resident, to the species nesting farther north 

 but which are present during the winter; and migrant, to those 

 merely passing through the county to their summer or winter quar- 

 ters. Visitant has been applied to a few species present at various 

 times but not falling into the four main divisions. The terms for 

 relative abundance have been chosen to express the frequency with 

 which the species are observed rather than their numerical abundance. 

 At the best the terms record only field impressions. Abundant, com- 

 mon, infrequent and rare have been used. Migration records have 

 been given in the form of inclusive dates, accompanied by the avail- 

 able records. This method was used on account of the rather wide 

 variation in many of the dates, indicating that the available data were 

 not exact enough for averaging, or that there is an unusual local varia- 

 tion in arrival. 



Order PYGOPODES, Diving Birds 

 Suborder Colymbi, Grebes 

 Family COLYMBIDAE, The Grebes 

 Colymbus nigricollis californicus, Eared Grebe (4)' 



Migrant; infrequent on the lakes of the Plains zone. The only definite 

 migration dates are May 12 and September 22, 1912. One specimen in the Uni- 

 versity collection was taken in 1908. Gale took several sets of eggs on June 19, 

 1890, just north of the county near Loveland. Reported to be a common breeder 

 at the Barr Lakes; will probably be found breeding occasionally in the county. 



Podilymbus podiceps, Pied-billed Grebe (6) 



Summer resident; infrequent in the summer; common in migration on the 

 lakes of the Plains. Noted between April 7 and October 16. Young birds were 

 seen by the writer near Gunbarrel Hill, August 3, 191 2; Gale found many nests 

 with eggs just north of the county, June 19, 1890. It nests "abundantly" at the 

 Barr Lakes. 



1 The "A.O.U. Numbers" are given in parentheses after the English name of each species. 



