FISHERY BULLETIN: VOL. 84, NO. 2 



x =JETTY 



OBSERVAT ION 

 POINT 



REGIONS 

 0A SC 



SB (D D 



o 



33 KM 

 TO HEAD 

 OF TIDE 



I 2 4"^ 2 



Figure 1.— Yaquina Estuary study regions. OAF indicates site of 

 smolt releases. 



quina Estuary, <30 pairs of western gulls (Bayer 

 1983) and an undetermined number of pigeon 

 guillemots also nested in association with manmade 

 structures. The typical nesting phenology of these 

 birds at Yaquina Head (which is about 6.5 km north 

 of Yaquina Estuary) has been examined by Scott 

 (1973) and Bayer (1983) with murres beginning to 

 fledge young in early July, gulls and pelagic cor- 

 morants in late July, and Brandt's cormorants and 

 pigeon guillemots in early to mid- August. However, 

 it would be invalid to assume that nesting in 1983 

 followed the chronologies of typical years because 

 nesting success for cormorants and murres was ab- 

 normally low in 1983 with eggs and young being 

 abandoned (Bayer 2 ). Although the nesting success 

 of gulls was not unusually low in 1983 (Bayer fn. 

 2), the chronology of their nesting might have been 

 different than in 1982. Thus, comparing 1982 and 

 1983 bird numbers at Yaquina Estuary for the same 

 stage of the nesting cycle would be tenuous. Brown 

 pelicans, Pelecanus occidentalis, and Caspian terns, 

 Sterna caspia, do not nest in this area. 



I divided the estuary and the area around its 

 mouth into four censusing regions (Fig. 1) with 

 region A having an area of about 1.8 km 2 ; region 

 B, 0.5 km 2 ; region C, 3.0 km 2 ; and region D, 3.2 



2 Bayer, R. D. In prep. Breeding success of seabirds along the 

 mid-Oregon coast concurrent with the 1983 El Nino. Unpubl. 

 manuscr. P.O. Box 1467, Newport, OR 97365. 



km 2 . I censused birds from observation points 

 where I could overlook the estuary or estuary mouth 

 with a 20 x telescope when glare, heat waves, and 

 water conditions did not obscure birds. I censused 

 the areas around the mouth of the jetties from an 

 observation point about halfway out on the south 

 jetty (Fig. 1). The boundaries of region A were 

 estimated -by using the distance to the first naviga- 

 tion buoys to the west of the jetties as a radius that 

 was about 1.5 km from the observation point and 

 1.0 km from the end of the jetties to estimate the 

 outer boundary. All taxa except pigeon guillemots 

 were censused during a single continuous sweep of 

 nonoverlapping portions of a region; pigeon guille- 

 mots were enumerated during two sweeps per por- 

 tion with the maximum number of the two sweeps 

 recorded. 



I censused "active" (see below) gulls and cor- 

 morants, nonflying common murres and pigeon 

 guillemots (including guillemots standing on station- 

 ary objects), roosting Caspian terns, all brown 

 pelicans, and all marbled murrelets, Brachyramphus 

 marmoratus. "Active" gulls were those that flew 

 over or sat in the water (gulls sitting on stationary 

 roosts were not included). Gull species included 

 western, glaucous-winged, L. glaucescens, and 

 western x glaucous-winged gull hybrids (Hoffman 

 et al. 1978). Cormorants present were usually either 

 Brandt's or pelagic cormorants, but some double- 

 crested cormorants, P. auritus, were also included. 

 "Active" cormorants were those on the water sur- 

 face or those making short flights in association with 

 a feeding flock; cormorants on transit flights 

 through a region or roosting on stationary objects 

 were not counted. Only nonflying murres and guille- 

 mots were included because others flew through 

 regions A and B without landing (and feeding). Al- 

 though roosting Caspian terns were obviously not 

 feeding, they were recorded because their numbers 

 were an index of the total numbers present and 

 because it was not possible to count foraging (i.e., 

 flying) Caspian terns accurately. There were 166 

 censuses during 37 d from 1 June to 16 September 



1982 at regions A-D during variable tidal conditions, 

 and 39 censuses within 2 h of low tides before 1500 

 Pacific Daylight Time (PDT) during 39 d from 1 June 

 to 30 August 1983 at regions A-C. Each census took 

 45-75 min, depending upon the number of birds 

 present. 



Comparisons of bird numbers between 1982 and 



1983 were only made for censuses within 2 h of low 

 tides before 1500 PDT. Comparisons were made 

 during the 1 June to 30 August period for brown 

 pelicans, "active" cormorants, "active" gulls, and 



280 



