Zbinden, N. & M. Salvioni
(* = Kurzbeitrag)
Bedeutung der Temperatur in der frühen Aufzuchtzeit für den Fortpflanzungserfolg des Birkhuhns Tetrao tetrix auf verschiedenen Höhenstufen im Tessin, Südschweiz.
(von 1994 bis 2006 vergeben)
Tetrao tetrix, reproductive success, temperature
Witterung, Temperatur, Bruterfolg, Brutperiode, Nestlingsnahrung
Tessin, Alpen, Schweiz, Finnland
The importance of temperature during the early chick-rearing period for the reproductive success of Black Grouse Tetrao tetrix at different altitude levels in the Ticino, southern Swiss alps. In their first days of life grouse chicks are very susceptible to outside temperature because thermoregulation has not fully developed. From 1981 to 2002 the relationship between reproductive success of Black Grouse and temperature was studied in the southern Swiss alps. Data showed that at different altitude levels temperature conditions in different time periods were particularly important: In northern Ticino (at the highest altitude) reproductive success depended on the mean daily temperature of five-day period 41 (20–24 July), in the central Ticino that of five-day period 39 (10–14 July) and in southern Ticino (at the lowest altitude) temperature of five-day period 37 (30 June to 4 July). At the altitude levels of the home ranges of Black Grouse hens temperature in these three five-day periods reached a mean of 11.4 to 11.8 °C. In northern Ticino five-day period 41 lies in the warmest season. In central and southern Ticino temperatures continue to grow after the five-day period most relevant for reproductive success. A comparison of the temperature conditions in the southern Swiss alps with those in Finland indicated different time constraints for alpine and northern birds: In Finland, before the start of egg-laying only one month with temperatures above 0 °C and thus increased assimilation of food plants is available to the hens, whereas in northern Ticino this period reaches more than two months. When spring arrives late Finnish hens are not able to build up sufficient reserves and lay eggs from which weak chicks hatch. On the other hand, temperature conditions in Finland after hatching are favourable for chick-rearing. In the southern Swiss alps the opposite is the case. Hens have enough time to build up reserves before egg-laying. In cool summers, however, temperature after hatching is often not high enough to enable a high number of chicks to survive the first critical days.
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