|
Résumé :
|
Little Grebe Tachybaptus ruficollis: Breeding bird, moderately migratory A slight long-term decline of resting birds is noticeable. The breeding status varies around an average of 51 pairs (between 28 to 78), tendency falling.Great Crested Grebe Podiceps cristatus: Inconspicuous breeding and migratory bird. Less than annual winter visitor and very sparse. Great Crested Grebes were present on only 9 % of excursions in December to February. No real proof of over-wintering. Steady increase of breeding population from less than 15 to a maximum of 100 pairs during the second half of the 20th century Also parallel increase of the results at the international waterfowl counts.Red-necked Grebe Podiceps grisegena: Migration in 2/3 of the years. 1 probable breeding attempt.Horned Grebe Podiceps auritus: Rare and irregular guest. Occurrence in only 28 % of years. 31 dates documented. One unusual over-summering.Black-necked Grebe Podiceps nigricollis: Winter occurrences are rare exceptions. Passage not noted. The average first observation occurs 6 days earlier during the last 20 years in comparison to 40 years ago. The breeding status is essentially steady, it varies from an average value of 46 (range 18 to 105); it amounted to an exceptional 100 only once. No long-term trend, however, a significant decline in the last 12 years.Breeding biology is commented upon: quality of habitat, nesting sites, availability of food, breeding success.
|