Artikel-Suche

Christian Harms

Zur Rufaktivität des Uhus Bubo bubo unter mitteleuropäischen Bedingungen – Lehren aus 1101 Verhörungen 2014–2018 im Raum Freiburg, Baden-Württemberg

2020

117

198–219

Key words
(von 1994 bis 2006 vergeben)

Rufaktivität, Balz, Fortpflanzung, Verhalten, Reviere, Umweltfaktoren, Witterung, Mondphasen, Beobachtungsaufwand

Schlagwort_Vogelart
(wissenschaftlich)

Bubo bubo

Schlagwort_Vogelart
(deutsch)

Uhu

Freiburg, Baden-Württemberg, Deutschland

deutsch

Abhandlung

Dusk vocalization of Eurasian Eagle-owls Bubo bubo under mid-European conditions – Lessons from 1100 passive auditory surveys 2014–2018 near Freiburg, Baden-Württemberg – A passive auditory survey project was carried out over 5 years, comprising 1101 listening sessions from October to March in 12 to 16 known and several suspected territories of Eagle-owls near Freiburg (Baden-Württemberg), to document dusk vocalizations. Calling-specific parameters such as start and end times, durations, numbers of calls, call bouts and positions as well as environmental parameters such as sky cover, temperature, wind strength, precipitation and moon phase were recorded as factors potentially affecting the vocalizations. Listening posts were on average 145 m (range 38–500 m) from the center of the territories (nest sites) to enable auditory perception as well as visual observation of the birds. Presence of Eagle-owls was established in 531 of 1101 listening sessions, 453 (85 %) of which were due to calling males, often combined with visual observations. Non-calling males were sighted in 51 sessions. Non-calling males, together with calling and sighted females, contributed 15 % of the observations confirming the presence of Eagle-owls. Calling males were heard more frequently in the first quarter of the year (Q1) than in autumn (Q4; 52.8 versus 30.5 % of listening sessions). Autumn calling consisted primarily of territorial calls, while intra-pair communication was more prevalent during the mating period in the first quarter of the year. Both calls and visual observations were more frequently recorded when the sky was clear, particularly in autumn. Environmental para­meters such as temperature (ranging from –5 to +20 °C), wind strength (Beaufort 0–4), precipitation (rainfall; fog with less than 100 m visibility) were not found to strongly affect the calling activity of male Eagle–owls. Moonlight was not found to stimulate the owls to call more. Males started calling before sunset more frequently in winter (Q1) than in autumn (Q4). This early calling was observed in about 25 % of the listening sessions with calls; most early calls were contact calls by which the males announced their presence to their mates rather than territorial calls, and early calling was generally short (on average 5.8 calls). On average, calling activity started 12 min after sunset (range –51 to +74, median 13). When the sky was fully clouded, males started calling about 7 min earlier compared to clear sky, and about 10 min earlier in the first quarter than in autumn. Calling activity ceased between 31 and 41 min after sunset, again earlier in the first quarter than in autumn, and earlier when the sky was covered. The mean duration of the males’ vocalization was 23–24 min and was not strongly affected by season and sky cover. The males produced on average 3.3 call bouts (of varying length) per listening session, from on average 2.3 call posts. The total number of male calls recorded was 21 667, 57 % of which occurred in the first quarter. The average was 58 calls per listening session, showing a similar distribution for both quarters, ranging from 1 to 391 calls per session. Our data allow to choose optimal listening times for efficient auditory surveys during the two main calling seasons. This study presents the first detailed account of the calling activity of Eagle-owls over several years in a mid-European environment.