S trachan and others 



Chapter 23 



At-Sea and Foraging Behavior 



meters, in a rocky substrate, and the longer dives were 

 observed in about 40 meters of water. Over a 4-year 

 observation period, Strachan (unpubl. data), observed dive 

 times in 20 to 50 meters deep water averaging about 31 

 seconds. Also at Ano Nuevo, Strachan (unpubl. data) observed 

 four birds, with a combined average dive time of 17 seconds, 

 ranging from 6-39 seconds. The shortest average time (1 1.2 

 seconds) was a pair of possible juveniles in shallow waters 

 of 2 to 5 m depth, up against the edge of a cliff. Those dives 

 in the deepest water (40-45 m) were also the longest, and 

 averaged 20.0 seconds. 



Pairs of birds resurface together on most dives, suggesting 

 that they likely keep in visual contact underwater. Carter and 

 Sealy ( 1990) found that dive times of individual birds averaged 

 27.8 seconds. Thoresen (1989), in a Washington study, observed 

 the mean time for a dive was 44 seconds (range 15-115). 



Dive depths Carter and Sealy (1984) found that murrelets 

 killed in gill nets at night were probably feeding near the 

 surface, as they were caught within 3 to 5 meters of the 

 surface. Sealy (1974) stated that they usually foraged in 

 areas that were sheltered from the prevailing winds and were 

 relatively shallow (<30 m in depth). In southeast Alaska, 

 Quinlan and Hughes (1984) found them most often in water 

 less than 100 meters in depth and along steep, rocky coastline. 

 In Prince William Sound, Alaska, Kuletz (199 la) found the 

 highest densities of foraging birds in waters less than 80 

 meters deep. Also in Alaska, Sanger (1987b) collected birds 

 in January and estimated that most birds had been feeding in 

 water of 18 to 45 meters deep. The birds had apparently 

 foraged from the mid depths, to occasionally at or near the 

 bottom, based on the prey species found in then- stomachs. 

 In Ano Nuevo Bay. California, Strachan (unpubl. data) found 

 the murrelets generally foraged in waters that ranged from 

 20-30 meters. 



Fish Holding 



Few observations have been published of birds on the 

 water holding fish. Carter and Sealy (1990) observed that 

 most murrelets seen holding fish were observed near dusk, 

 just before they fly to their nest to feed nestlings. A few 

 birds were observed holding fish at dawn and later in the 

 morning. They inferred that some individuals may feed chicks 

 during the day because they felt that adults holding fish can 

 not usually capture more fish. Carter and Sealy (1990) felt 

 that increased fish holding by birds toward dusk coincided 

 with the decrease in overall numbers of birds in the foraging 

 area. Larger flocks sometimes included birds holding fish 

 that were not feeding, although most birds that held fish 

 were alone or in pairs. McAllister (unpubl. data) has recorded 

 pre-dusk fly ways where hundreds of fish-holding murrelets 

 are counted as they leave foraging areas in Icy Strait, Sumner 

 Strait, and in Frederick Sound in Southeast Alaska, heading 

 towards their presumed nesting areas. At numerous locations, 

 McAllister (unpubl. data) has recorded continuous flyway 

 activity (averaging more than 20 birds per minute), with the 

 majority of birds holding fish. 



On a few occasions, birds have been reported holding 

 more than one fish in their bill. Thoresen (1989) observed a 

 bird with two fish and a bird with three fish held crosswise, 

 both on the water's surface and flying. Other observations of 

 multiple fish in the bill include Carter (pers. comm.), Cody 

 (1973), Forma (pers. comm.), and Savile (1972). 



Foraging Influences 



Adjacent inland habitat Densities of the Marbled 

 Murrelet in specific geographic areas during the breeding 

 season appear to be related to the adjacent nesting habitat 

 (Carter and Sealy 1990; Ralph and Miller, this volume). It is 

 also very probable that foraging locations are dependent 

 upon prey habitat or availability, but no research has been 

 conducted on this subject to date. 



Weather Throughout their range, murrelets have been 

 observed foraging in all weather conditions normal for that 

 habitat They have also been seen foraging in extreme weather 

 conditions. McAllister (unpubl. data) has recorded foraging 

 at night in sub-freezing conditions, with 40-60 knot easterly 

 winds blowing out from the Taku River Valley. The birds 

 were foraging on the herring schools that were feeding in the 

 interface between marine and fresh water. Due to the 

 topography, nearby waters within 4 km were relatively calm, 

 yet the birds chose to be active at night in the rough weather 

 and seas. 



Times of day Birds appear to forage at all times of the 

 day, and in some cases during night hours, presumably when 

 there is enough ambient light to capture prey. Some observers 

 have hypothesized that murrelets move from one feeding 

 area to another during the early morning and late afternoon 

 periods (Carter 1984, Carter and Sealy 1984, Prestash and 

 others 1992). On the other hand, they may be staging in an 

 area in the early morning near the nesting area, then moving 

 out into foraging areas. Off the California coast, six birds 

 with radio transmitters did not forage during the night in 

 June or July (Ralph, unpubl. data), rather, the foraging was 

 confined to the daylight hours. 



Topography We have observed consistent densities of 

 birds utilizing the lee of protected headlands in California, 

 as has Kuletz (pers. comm.) in Alaska. We have noticed, but 

 not quantified, that the wind conditions could be a factor for 

 greater bird densities in the lee of headlands. Carter and 

 Sealy (1990) speculated that prey also concentrates in sheltered 

 waters. Certainly concentrations of birds are likely due to 

 the availability of prey at the rip-current lines and in the tidal 

 eddies that are established to the downwind of such features. 

 In Oregon, Strong and others (1993) found that the highest 

 densities of murrelets were found adjacent to beaches or 

 mixed beach and rocky shore areas. 



Non-Foraging Behavior 



Coalescence 



An interesting phenomena that has been noted by a few 

 researchers is that during the breeding season, about an hour 



USDA Forest Service Gen. Tech. Rep. PSW-152. 1995. 



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