Larus Heermanni Research Articles

Physiological Responses of Embryonic Heermann's Gulls to Temperature

Oxygen consumption, heart rate, and thermal tolerance were measured in week-old embryos of Heermann's gull (Larus heermanni). Heart rate and oxygen consumption are temperature independent between 30 and 40 C and average 120 beats/min and 1.87 cm³ O₂/(egg·h). Below 30 C, these rate processes become strongly temperature dependent, and the heart stops beating when cooled to 7-13 C. The beat recovers when the embryo is rewarmed, even after 1 h at 6 C. The heart beat stops when the embryo is heated above 40.0-41.6 C but recovers with cooling. However, the beat does not recover after the embryo has been heated to 43 C for 1 h. The thermal independence of embryonic function over the 30-40 C range minimizes disruptions associated with variation of temperature during incubation. Unattended eggs at night may chill to temperatures which cause cessation of heart beat, but such exposure is not lethal if the eggs are rewarmed. Exposure to radiant heat during the day can rapidly raise egg temperature to levels which kill the embryo. Thus, an important aspect of incubation by adult Heermann's gulls is shading of the eggs and prevention of overheating.

Discovery of a Golden Eagle Nest on the Alaska Peninsula

Feeding relationships between Snowy Egrets (Egretta thula) and Red-breasted Mergansers (Mergus serrator), often involving other waterbirds as well, have been the subject of published comment on several recent occasions. Christman (Condor 59:343, 1957) described an occurrence in San Diego County, California. Parks and Bressler (Auk 80:198, 1963) and Emlen and Ambrose (Auk 87:164, 1970) were concerned with similar feeding movements in Florida, the former also citing an instance involving Hooded Mergansers (Lophodytes cucullatus). Another, but more complex, example was observed early in the morning on 2 December 1972 at Bahia de la Concepci6n (ca. 26038' N, 111050' W) on the Gulf of California in central Baja California. The principal element consisted of about 40 Red-breasted Mergansers which were swimming together, with their heads often below the water, parallel to the rocky shoreline and ranging from 10 to 30 ft from the shore. Moving along the shore abreast of the ducks were 7 Snowy Egrets, a Reddish Egret (Dichromanassa rufescens), 18 Heermann's Gulls (Larus heermanni), and 3 Ring-billed Gulls (Larus delawarensis). This assemblage was gradually augmented by another Reddish Egret, two Brown Pelicans (Pelecanus occidentalis) and a Double-crested Cormorant (Phalacrocorax auritus). The pelicans and cormorant stayed on the open-water side of the ducks. When the mergansers found fish and commenced diving, the whole scene became one of frenzied activity. As the fish sought to escape, some fled toward the shore, and the herons moved into shallow water and darted about, snatching them up. The pelicans and cormorant fed on fish which moved toward deeper water. The Heermann's Gulls showed an interest in the mergansers but did not obtain any food from them; they did successfully harass the pelicans, and both they and the Ring-billed Gulls robbed the Snowy Egrets. Both species of gulls also waded in to get food from the shallow water, perhaps bits of fish. It was not possible to examine any of the fish but they appeared to be small, about 3 inches in length. After a few minutes, the school of fish was dissipated or moved to deeper water. The procession then moved on. Three such scenes of activity involving the same group of birds were observed in the 40 min of observation.

Symbiotic Relationships within a Mixed Waterfowl Assembly

Feeding relationships between Snowy Egrets (Egretta thula) and Red-breasted Mergansers (Mergus serrator), often involving other waterbirds as well, have been the subject of published comment on several recent occasions. Christman (Condor 59:343, 1957) described an occurrence in San Diego County, California. Parks and Bressler (Auk 80:198, 1963) and Emlen and Ambrose (Auk 87:164, 1970) were concerned with similar feeding movements in Florida, the former also citing an instance involving Hooded Mergansers (Lophodytes cucullatus). Another, but more complex, example was observed early in the morning on 2 December 1972 at Bahia de la Concepci6n (ca. 26038' N, 111050' W) on the Gulf of California in central Baja California. The principal element consisted of about 40 Red-breasted Mergansers which were swimming together, with their heads often below the water, parallel to the rocky shoreline and ranging from 10 to 30 ft from the shore. Moving along the shore abreast of the ducks were 7 Snowy Egrets, a Reddish Egret (Dichromanassa rufescens), 18 Heermann's Gulls (Larus heermanni), and 3 Ring-billed Gulls (Larus delawarensis). This assemblage was gradually augmented by another Reddish Egret, two Brown Pelicans (Pelecanus occidentalis) and a Double-crested Cormorant (Phalacrocorax auritus). The pelicans and cormorant stayed on the open-water side of the ducks. When the mergansers found fish and commenced diving, the whole scene became one of frenzied activity. As the fish sought to escape, some fled toward the shore, and the herons moved into shallow water and darted about, snatching them up. The pelicans and cormorant fed on fish which moved toward deeper water. The Heermann's Gulls showed an interest in the mergansers but did not obtain any food from them; they did successfully harass the pelicans, and both they and the Ring-billed Gulls robbed the Snowy Egrets. Both species of gulls also waded in to get food from the shallow water, perhaps bits of fish. It was not possible to examine any of the fish but they appeared to be small, about 3 inches in length. After a few minutes, the school of fish was dissipated or moved to deeper water. The procession then moved on. Three such scenes of activity involving the same group of birds were observed in the 40 min of observation.

First Records of Heermann's Gull (Larus heermanni) for Arizona

First Records of Heermann's Gull (Larus heermanni) for Arizona