| י254) ריסה שחורת-רגל | ||||||||||
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:ריסה שחורת-רגל הבוגר דומה לשחף אפרורי, אלא שנראה יותר עדין . וחסר את הכתמים הלבנים בקצות כנפיו השחורים . אברות זנבו המרכזיות קצרות משאר אברות הזנב . עיניו חומות כהות מוקפות עיגול אדום, מקורו צהוב ורגליו שחורות המעוף מרשים וקליל בדומה לשחף האגמים, בתקופת הקינון האויר . Kittiwake מלא בקריאות "קיט-אוייק" ומכאן שמה האנגלי . בית גידולה אזור ארקטי עם מים ממוזגים. דוגרת בחופים בעלי צוקים תלולים . בארץ עוברת אורח נדירה מאוד וחורפת נדירה בחופי ים התיכון ומפרץ אילת ... ואת השחף ... ויקרא י"א, 16 | ||||||||||
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Subspecies and Distribution.
R. t. tridactyla Canada and NE USA E through Greenland to W and N Europe to Zemlya. Winters to Sargasso Sea and W Africa. R. t. pollcaris NE Siberia, Kamchatka, Sea of Okhotsk and Kuril Is through Bering Sea to Alaska. Winters S to East China Sea and NW Mexico.םםםםםםםםםםםםםםםםםםםםםםםםםםםםםםםםםםם םםםםםםםםםםםםםםםםםםםםםםםםםםםםםםםם | ||||||||||
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Descriptive notes.
White-headed gull, with short legs. 40 cm, 300-510 g, wingspan 90-95 cm. Mantle and upperwing-coverts blue grey, outer wing slightly paler, with sharply defined, triangular, all black wingtip. Bill yelow, legs blackish, iris dark brown, with narrow red eye-ring. Distinguished from R. brevirostris by paler primary bases contrasting more strongly with grey wing-coverts and black wingtips, also by leg colour. Race pollicaris larger, with more extensively black primaries. Habitat. Breeds on coasts as far N as open wate occurs, preferring high, steep cliffs with narrow ledges. Nests on glacier or snowbank face when it covers traditional cliff sites. Access to fresh water important. Highly pelagic in non-breeding season,when usually not in sight of land. Food and Feeding. Fish and marine invertebrates. Outside breeding season also takes planktonic invertebrates, and has recently begun to exploit sewage outfalls and fishing vessels, and to take other offal in estuaries. Many species of fish recorded in diet, but sandeels, capelin and herrig particularly important. Main fishing methods are surface-dipping with or without foot-pattering, and plunge-diving to one m below surface. Breeding. May-Jun, depending on latitude. Usually breeds in huge colonies, 10.000 occasionally over 100.000 pairs. Nest site on narrow cliff ledge, or on ledge or window-sill of building or factory. Elaborate nest, incorporating grass and feathers. 2 eggs, incubation 24-28 days. Downy chick not cryptic, white with greyish back and wings. Guarded continuously for 4 weeks. First breeding usually at 4 years. Movements. Post breeding dispersal from colonies to open ocean, usually well away from coast. Birds from Greenland remain in Davis Strait until Nov, returning in Mar. Species is found across entire N Atlantic and N Pacific in winter, and many birds congregate at rich fishing banks off Nova Scotia. Status and Conservation. Not globally threatened. Overall world population estimated at least 6.000.000 pairs. Israel. In Israel subspecies R. t. tridactyla. Rare winter visitor and very rare passage migrant, at Mediterranean shores and Gulf of Eilat. |
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