Efficient Evaporative Cooling and Pronounced Heat Tolerance in an Eagle-Owl, a Thick-Knee and a Sandgrouse

Avian evaporative cooling and the maintenance of body temperature (Tb) below lethal limits during heat exposure has received more attention in small species compared to larger-bodied taxa. Here, we examined thermoregulation at air temperatures (Tair) approaching and exceeding normothermic Tb in three larger birds that use gular flutter, thought to provide the basis for pronounced evaporative cooling capacity and heat tolerance. We quantified Tb, evaporative water loss (EWL) and resting metabolic rate (RMR) in the ∼170-g Namaqua sandgrouse (Pterocles namaqua), ∼430-g spotted thick-knee (Burhinus capensis) and ∼670-g spotted eagle-owl (Bubo africanus), using flow-through respirometry and a stepped Tair profile with very low chamber humidities. All three species tolerated Tair of 56–60°C before the onset of severe hyperthermia, with maximum Tb of 43.2°C, 44.3°C, and 44.2°C in sandgrouse, thick-knees and eagle-owls, respectively. Evaporative scope (i.e., maximum EWL/minimum thermoneutral EWL) was 7.4 in sandgrouse, 12.9 in thick-knees and 7.8 in eagle-owls. The relationship between RMR and Tair varied substantially among species: whereas thick-knees and eagle-owls showed clear upper critical limits of thermoneutrality above which RMR increased rapidly and linearly, sandgrouse did not. Maximum evaporative heat loss/metabolic heat production ranged from 2.8 (eagle-owls) to 5.5 (sandgrouse), the latter the highest avian value yet reported. Our data reveal some larger species with gular flutter possess pronounced evaporative cooling capacity and heat tolerance and, when taken together with published data, show thermoregulatory performance varies widely among species larger than 250 g. Our data for Namaqua sandgrouse reveal unexpectedly pronounced variation in the metabolic costs of evaporative cooling within the genus Pterocles.

Diet composition of the Pharaoh Eagle Owl, Bubo ascalaphus (Strigiformes, Strigidae) in a Steppe region of Algeria

The diet composition of Pharaoh Eagle Owl (Bubo ascalaphus) was investigated in a semiarid area of North-western Algeria. A total of 65 pellets regurgitated by the B. ascalaphus were analysed, 288 food items were composed primarily of mammal remains (4 rodents, 1 bat and insectivore, 93.7%), and 1 bird species (passerine, 6.3%). The most frequent prey among the mammals were rodents (83.3%), which included Mus musculus (59.7%), Meriones shawi (11.1%), Meriones libycus (11.1%) and Jaculus jaculus (1.4%). The rodents were the most important prey items in biomass (91.4%), M. shawi made up to 41.9% of the total biomass. We may conclude that the Pharaoh Eagle Owl relies, in its feeding, very broadly on small mammals, completed by other groups.

Population dynamics of an island population of water voles Arvicola amphibius (Linnaeus, 1758) with one major predator, the eagle owl Bubo bubo (Linnaeus, 1758), in northern Norway

Predator–prey relationships are of great significance to ecosystems, and their effects on the population dynamics of voles and lemmings (Microtinae) in Boreal and Arctic environments have long been of particular interest. A simple ecosystem with one major prey and one major predator could be an ideal setting for a study of their interactions. This is the situation on several small islands on the coast of northern Norway just below the Arctic Circle, with populations of water voles Arvicola amphibius preyed upon by the eagle owl Bubo bubo. The population dynamics of the water vole was studied by trapping and tagging in 2003–2018, eagle owl pellets were collected for analyses, eagle owl breeding attempts were recorded, and some weather variables collected from official recordings. After having been introduced well into the study period, the number of sheep Ovis aries was also recorded. Water voles were the main prey of the eagle owl, with 89% occurrence in pellets, with an overrepresentation of adults and males. Both predation, sheep grazing and extreme weather events influenced the vole population. Predator exclusion, as happened in three summers due to an intensive radio tracking study, especially increased the number of surviving young (in particular from the early cohorts) and the mass of adults. Extreme weather events, such as flooding in summer and deeply frozen ground in winter, most significantly reduced vole populations. Sheep grazing may exacerbate the effects of predation. A similar multitude of factors may affect populations of other rodent species as well.

First evidence of hunting of a Crested Indian Porcupine by an avian predator: The Eurasian Eagle Owl

Encounters between birds of prey and porcupines are rarely documented, and so far only in North America. At least 39% of such encounters lead to death of the attacker. We present first evidence for similar encounters between The Eurasian Eagle Owl and the Indian Crested Porcupine, suggesting that young porcupines may occasionally serve as potential prey for the owl.

Use of DNA metabarcoding of bird pellets in understanding raptor diet on the Qinghai-Tibetan Plateau of China

Background Diet analysis is essential to understanding the functional role of large bird species in food webs. Morphological analysis of regurgitated bird pellet contents is time intensive and may underestimate biodiversity. DNA metabarcoding has the ability to circumvent these issues, but has yet to be done. Methods We present a pilot study using DNA metabarcoding of MT-RNR1 and MT-CO1 markers to determine the species of origin and prey of 45 pellets collected in Qinghai and Gansu Provinces, China. Results We detected four raptor species [Eurasian Eagle Owl (Bubo bubo), Saker Falcon (Falco cherrug), Steppe Eagle (Aquila nipalensis), and Upland Buzzard (Buteo hemilasius)] and 11 unique prey species across 10 families and 4 classes. Mammals were the greatest detected prey class with Plateau Pika (Ochotona curzoniae) being the most frequent. Observed Shannon’s and Simpson’s diversity for Upland Buzzard were 1.089 and 0.479, respectively, while expected values were 1.312 ± 0.266 and 0.485 ± 0.086. For Eurasian Eagle Owl, observed values were 1.202 and 0.565, while expected values were 1.502 ± 0.340 and 0.580 ± 0.114. Interspecific dietary niche partitioning between the two species was not detected. Conclusions Our results demonstrate successful use of DNA metabarcoding for understanding diet via a novel noninvasive sample type to identify common and uncommon species. More work is needed to understand how raptor diets vary locally, and the mechanisms that enable exploitation of similar dietary resources. This approach has wide ranging applicability to other birds of prey, and demonstrates the power of using DNA metabarcoding to study species noninvasively.

Bionic Design and 3D Printing of Continuous Carbon Fiber-Reinforced Polylactic Acid Composite with Barbicel Structure of Eagle-Owl Feather

Inspired by eagle-owl feather with characteristics of light weight and high strength, the bionic continuous carbon fiber-reinforced polylactic acid composite with barbicel structure was successfully 3D printed. Under the action of external load, angles between barbicels and rachis structure of eagle-owl feather decreased, which consumed a part of energy and built structure base of bionic feather structure model with a certain arrangement angle of continuous carbon fiber. Variation of bionic structure model design parameters significantly affected the mechanical properties of the 3D printing bionic composites. The relatively low continuous carbon fiber content on tensile force direction restricted enhancement of tensile strength of bionic composite. However, attributed to different angle arrangement of continuous carbon fiber, the propagation of cracks in bionic composite was hindered, exhibiting high impact resistance. The effective and feasible bionic feather design and 3D printing of continuous carbon fiber-reinforced polylactic acid composite extended the corresponding application in the areas with high impact loads.