Decline of Common buzzards
In 2014 and 2015 the breeding population and success of the Common buzzard was investigated for two larger study areas in the region of Schleswig for which previously recorded data from prior decades was available. Thereby a decline in the Common buzzard population was detected that had reached a level of a third of the population recorded at the turn of the millennium. One possible cause for this decline, next to conversion of agricultural lands (from grazing to corn production for biogas plants) and mortality caused by wind turbines, could be the detected low possibility of nestling survival.
Since April 2015 BioConsult SH is investigating possible causes for the decrease in breeding success in a three-year project. Next to an ongoing breeding population monitoring and a determination of the brood and clutch size, video cameras are being used to monitor buzzard nests and to test the following hypotheses that might be explanations for the low breeding success:
1. change of land use with a decline in the numbers / a worsened reachability of the main prey field vole
2. predation of young birds (Eagle owl, goshawk, mammals) in the nestling period
3. low hatching success (caused by e.g. toxins)
Per breeding season ten video cameras are positioned at buzzard nests. These cameras enable a continuous recording of the nestling period (from hatching to fledging). Using this approach, the hypotheses mentioned above can be tested by recording the following breeding biology data:
1. species, mass of food items and timing of feeding,
2. cause and time of chick disappearance, especially when predation occurs
3. determination of the chick-egg-ratio
The images recorded by the camera are transmitted via a cable that is fixed to the tree trunk into a crate on the ground that contains a power and a recording unit.
Videos 2017 (third year of the study)
The year 2017 is characterized by the following three clips of the nestling phase of one specific nest near Bünge/ Dörpstedt.
Insufficient foodsupply for three
This clip underlines the insufficient food supply of larger broods in spring 2017. At 6th of July the female breeding bird is landing near the nest without any prey for the fifths time within nine hours. One nestling only gets 40 g instead of the approximately necessary prey mass of 150 g/day. The condition of the nestlings is already bad regarding the nest day with continuous rainfall and low temperature.
Extreme weather event
The next day at the 7th of July the smallest chick is starved and is fed to the sibling. A second chick will not survive this day either. An extreme weather event with temperatures as low as 13 °C, stormy winds and continuous rainfall over 20 hours caused these chick losses. At this specific day 8 out of 26 chicks under video control died.
This clip demonstrates the sufficient food supply of the oldest – meanwhile full grown – chick. See the delivered mole at the 2nd July.
Videos 2016 (second year of the study)
In the following video a goshawk attacks two Common buzzard nestlings in their nest and eventually takes away one (sequence: "2016 Prädation Habicht"). This is the only recorded attack by a goshawk in 2016, while another nestling was taken by an Eagle owl (not shown).
Food supply for the young Common buzzards was scarce, because 2016 was a bad year for voles. In the following video the wet and freezing nestlings quarrel about a vole. One of the nestlings fends off his siblings and eventually feeds on the vole alone (sequence: "2016 Futterstreit").
Two hours later the weakest bird in the nest has died of starvation and falls out of the nest (sequence: "2016 Kücken fällt aus dem Nest"). In 2016 a total of eight nestlings died of starvation in the monitored nests. In 2015 no nestling had died of starvation.
Videos 2015 (first year of the study)
In this video a young Common buzzard is attacked and killed by an Eagle owl in its nest. The adult bird behaves very passively during the attack and does not display any behaviour to chase off the owl. The Eagle owl appears at about 0:18. Later on (at about 1:45) the adult Common buzzard is driven out of the nest. The second young bird is taken from the nest at a later point (see video: 'Prädation Jungvogel 2').
In this video the second young Common buzzard is taken from the nest by the Eagle owl (at about 0:33). This video was recorded after the video 'Prädation Jungvogel 1' (see above).
Ursachenforschung zum Rückgang des Mäusebussards in Schleswig-Holstein
148th Annual Meeting of the “Deutsche Ornithologische Gesellschaft”, Konstanz, Germany (2015)Download document
Projekt Ursachenforschung zum Rückgang des Mäusebussards im Landesteil Schleswig
Jagd und Artenschutz 2015 p. 94-97Download document