Cover photo: Common Loon Gavia immer with prey. Photo: Torborg Berge. Diet and aspects of feeding behaviour of Yellow-billed Loons Gavia adamsii and Common Loons G. immer were compared during the non-breeding season in coastal Norway. Stomach contents from 14 Common Loons and 13 Yellow-billed Loons showed that fishes constituted the main prey of both species. However, saithe Pollachius virens constituted a major component of the diet of the Yellow-billed Loon, whereas wrasses (Labridae), flatfish (Pleuronectidae), and sandeel Ammodytes tobianus were important prey for Common Loons. Common Loons also frequently included crustaceans and sometimes molluscs in their diet. We tested the hypothesis that the Yellow-billed Loon, with its more upturned bill, feed more on bottom-living prey than the Common Loon. Contrary to the hypothesis, stomach contents indicated that more bottom-living prey were taken by Common Loons, and Yellow-billed Loons seemed to prey more on pelagic fish. A difference in prey selection was consistent with field observations that Yellow-billed Loons often fed in water judged too deep for bottom-feeding, social groups were often synchronized when feeding, and their stomach contents contained only a few gastroliths compared to Common Loons. Species differences in number of gastroliths indicate that Yellow-billed Loons are feeding on softer food such as pelagic fish, whereas Common Loons are feeding on crustaceans and the more armoured and spiny fishes occurring in bottom habitats.
Cover photo: Golden Eagle Aquila chrysaetos. Photo: Henning Dunker. During breeding, most birds have to visit and leave the nest regularly to forage or to provision young. Nesting activity may help competitors or predators to locate the nest and offspring, selecting for parents to behave secretively. The present study reports observations of secretive flight behaviour of Golden Eagles Aquila chrysaetos during a long-term study in Norway based on more than 1500 hours of observation in the nesting areas of 16 pairs of eagles. By a combination of absence from the nest and secretive flights, the eagles seemed to avoid being observed near their nest, as shown by observations of 14 cases of secretive flights from 10 nesting areas. Silhouettes against the sky near the nest seemed to be avoided by the eagles, either by downhill flight in the forest below the nest and skyline, or by a fast approach to the nest, the latter either by a sideway descent or by falling like a stone from a high altitude above the nest within a few seconds. Secretive behaviour may help to avoid long-distance discovery and nest predation, in particular by intruding non-territorial eagles, but also by other raptors and Ravens Corvus corax, as well as to avoid disturbance by humans. Secretive behaviour creates serious challenges for monitoring of Golden Eagle populations, where each pair of eagles usually have several nest sites and where often less than 50% of the pairs are breeding in a given year.
Cover photo: A Peregrine Falcon Falco peregrinus landing on a radio antenna. Photo: Bjarne Emil Time. In November-December 2019, a Peregrine Falcon Falco peregrinus hunted close to the center of Bryne, a small town in southwest Norway. During winter, several thousand corvids normally roosted together in the city’s park area. The hunts took place in the dark, after sunset and before sunrise. In this 30-day study, the falcon used a sit-and-wait strategy to hunt roosting corvids. The hunt started each time from the top of a 43 m high antenna near to the park and my apartment. The falcon then brought prey items to a balcony on a tall office building in the city centre, and to the same plucking and eating site after each kill. Sensitive cameras documented the activity of the falcon and its prey which were always Jackdaws Corvus monedula. One camera was mounted by the antenna and two cameras were deployed on the balcony. The attacks were registered as successful if the falcon returned with prey, or otherwise as unsuccessful. The falcon made a total of 42 attacks. A subset of 18 attacks ended with a return to the balcony, of which 13 were successful, resulting in a hunting success of 31% (13/42). Overall, 54% of all kills occurred in the dark before sunrise, and most of the prey were killed in December (77%). The ratio of time spent on successful hunting to total hunting time was 79 to 308 minutes, giving a hunting time efficiency of 26%. On average, the falcon used 6 minutes per successful kill, with a range between 1 to 16 minutes.
Cover photo: Great Skua Catharacta skua. Photo: Terje Lislevand. A better understanding of how birdwatchers identify species of birds in flight may support the development of machine learning algorithms for automated identification from camera-tracking systems for bird monitoring and mitigation. Norwegian birdwatchers scored the importance of 18 criteria for identifying species of birds in flight in an online anonymous survey. Responses were analysed using an Analytical Hierarchy Process and Bayesian Belief Networks. Species identification was first affected by a seasonal expectation as to which species may be observed during a birding trip. Criteria linked to bird’s appearance were most important for species identification, including plumage colouration or patterns; body and wing shape; beak, neck and tail shape. However, flight pattern and speed may provide additional information. A hierarchical approach to categorisation and species identification may improve processing time of automated algorithms.
Cover photo: Hooded Crow Corvus cornix. Photo: Terje Lislevand. Non-vocal sounds made by rapid closing of the bill are well known among many bird species, including several corvids. However, this is the first documentation of bill clapping by a Hooded Crow Corvus cornix during aggressive encounters with a conspecific. The aggression level was low, and the bill clapping was accompanied by a weak rolling ‘r’ sound.
