Breeding adaptations of Franklin's gull (larus pipixcan) to a marsh habitat

摘要: Abstract The behaviour and ecology of Franklin's gull were studied at Agassiz National Wildlife Refuge in northwestern Minnesota to determine the adaptations species for nesting marshes. Two factors seemed be important colony site selection: cattail dispersion pattern density. gulls prefer nest areas closest open water. number nests per unit area decreased as density increased. Nest selection is dependent on aggression visibility. Visibility from level result placement height. distance between was directly correlated with Aggression by lowered experimentally decreasing visibility raised increasing platforms constructed material, attached stems. material added throughout incubation brooding period. Material usually following relief. egg laying period 6 28 May. There more synchrony sub-areas than a whole. Successive eggs clutches laid 24- 48-hr intervals. during season pairs filled that not defended. Territorial defended an up 10 m their stations prior laying, but only within 3 incubation. Both members incubated cared young. 24 days. primary predators adults young marsh hawk, great horned owl mink. do eat or gulls. Adults fed earthworms, insects grain. Most marked 16 km colony. Chicks primarily earthworms. hatching 30 May 21 June. all ages tested visual cliff apparatus able perceive drop. 30-degree incline walked it when days old younger, down 12 age older. Brood mobility less ground In undisturbed chicks remained until they 25 although capable swimming shortly after hatching. Individual recognition parents appeared later this ground-nesting accepted alien (experimentally exchanged) younger about 14 own over age. larger older broods own, well mixed ages. began react differently strange breeding chronology compressed compared other Possible pressures affecting are discussed. marsh-nesting typical ground-and cliffnesting gulls; possibility ancestral may have been nester