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Acoustic spatial capture-recapture (SCR) methods appear ideally suited for estimating population trends of cryptic species that are difficult to monitor. Despite evidence suggesting acoustic SCR offers greater precision over estimates obtained through distance sampling or mark-recapture approaches, it has seldom been applied to avian taxa. Here we assess the utility of acoustic SCR for estimating population density of owls, a group of birds for which population estimates are generally lacking. We conducted passive acoustic surveys for Barred Owls (Strix varia) and Great Horned Owls (Bubo virginianus) over the spring breeding seasons of 2020–2021 in a protected park in Georgia, USA. We used a combination of acoustic discrimination techniques to identify individuals, including spectrogram cross-correlation, hierarchical clustering, and visual scanning. The resulting estimates of the density of Great Horned Owl individuals (0.28 ± 0.026 [SE] per km2) were consistent with population density estimates from previous studies in other parts of the species' range. However, our methods appeared unsuitable for distinguishing Barred Owl individuals, which prevented estimation of population density for this species. We provide recommendations to improve acoustic sampling and individual discrimination of owls and suggest that acoustic SCR offers important advantages over conventional methods for monitoring some cryptic birds. Los métodos de captura-recaptura espacial (CRE) acústica parecen ser ideales para estimar las tendencias poblacionales de especies crípticas que son de difícil seguimiento. A pesar de la evidencia que sugiere que la CRE acústica ofrece mayor precisión que las estimaciones obtenidas mediante muestreo de distancia o enfoques de marcado-recaptura, ésta rara vez se ha aplicado a taxones aviares. Evaluamos la utilidad de la CRE acústica para estimar la densidad poblacional de búhos, un grupo de aves para el cual generalmente faltan estimaciones poblacionales. Realizamos estudios acústicos pasivos para Strix varia y Bubo virginianus durante las temporadas de cría en las primaveras del 2020 y 2021 en un parque protegido de Georgia, EEUU. Utilizamos una combinación de técnicas de discriminación acústica para identificar individuos, incluyendo correlación cruzada de espectrogramas, agrupacion jerárquica y escaneo visual. Las estimaciones resultantes de la densidad de individuos de B. virginianus (0.28 ± 0.026 [EE] por km2) fueron consistentes con las estimaciones de densidad poblacional obtenidas en estudios realizados previamente en otras áreas del rango de distribución de la especie. Sin embargo, nuestros métodos parecieron inadecuados para distinguir individuos de S. varia, lo que impidió la estimación de su densidad poblacional. Ofrecemos recomendaciones para mejorar el muestreo acústico y la discriminación individual de búhos, y sugerimos que la CRE acústica ofrece importantes ventajas sobre los métodos convencionales utilizados para el seguimiento de algunas aves crípticas. [Traducción del equipo editorial] [ABSTRACT FROM AUTHOR]

Birds show huge variation in color displays evolved for communication. However, among colored phenotypic traits, eyes remain largely overlooked, with only a few studies suggesting a potential signaling function or a role in mate recognition and crypsis. Iris color is a remarkably striking feature in the wholly cryptic pattern of many owls, and may potentially play a signaling function, a possibility so far neglected. Here, we studied variation and potential signaling of iris yellowness as an indicator of quality in parent-offspring communication and other social contexts in the Little Owl (Athene noctua) and Eurasian Scops-Owl (Otus scops). Yellowness did not differ between the sexes; however, adults of the two species had more intensely yellow irises than owlets. Most of variation in iris yellowness of owlets occurred between rather than within nests and seemed to be linked to parental qualities of Little Owls, but was unrelated to condition among Eurasian Scops-Owl owlets. In adults, however, we found that iris yellowness of females was positively associated with nest success (an index of female fitness) in Little Owls, but not in Eurasian Scops-Owls. This study suggests that iris color variation is unlikely to play a role in parent-offspring communication for these two owl species, but that iris yellowness of female Little Owls may potentially play a signaling role in social contexts, a possibility that should be studied in the future. [ABSTRACT FROM AUTHOR]

Scavenging is an important ecological function that increases individual fitness and transfers energy between trophic levels. Scavenging by owls has been documented opportunistically through direct observations, camera trapping, and pellet analyses, but it is unknown how frequent or widespread the behavior is. We documented three new scavenging events from North America and Europe, and also performed a systematic literature review of the reports documenting scavenging by owls. The number of such reports was similar in each decade from the 1970s to the 2000s, but the decade of the 2010s had more reports than all previous decades combined. Owls scavenged primarily on mammals (81%), followed by birds (16%) and reptiles (3%); almost half (47%) of carrion scavenged were Artiodactyla (hoofed mammals) and most of the species scavenged were larger than the feeding owl. Most reports documenting scavenging by owls were from either Europe (n=14) or North America (n=11), with few reports from Asia (n=2), South America (n =2), or Australia (n=1), and none from Africa. The most frequent type of report was direct observations (n= 14), followed by camera trapping (n=9) and pellet analyses (n=6). Our review indicates that scavenging is a widespread behavior among owl species, but most observations were opportunistic, suggesting that additional incidents of scavenging by owls are likely unobserved. Further research is needed to establish the frequency of scavenging by owls and the effects that scavenging may have on owl populations and scavenging communities. [ABSTRACT FROM AUTHOR]

The article focuses on a study on home-range size and territorial calling of Southern BooBooks (Ninox Novaeseelandiae). The researchers analyzed the adjacent nesting home ranges of four radio-tagged Southern BooBooks in a woodland in Canberra, Australia. During the 418 observation nights, they recorded the spatial locations and bouts of territorial calling which were used to compute the home ranges and core areas using minimum convex polygons and characteristic hull polygons. It was found out that 26% of the vocalizations of the boobooks occurred within core areas while 56% occurred within the home range. Based from the percentage of boobook calls observed on or outside home-ranged boundaries, it is concluded that owls actively defended areas which are larger than their core areas.

The article offers information on strange nests of raptor around the world. It notes that there are various reports of raptors utilizing unusual nesting materials including paper money, rags, and metals and nesting area. It mentions several odd nesting area of raptors including Steppe Eagles (Aquila nipalensis) and Upland Buzzards' (Buteo hemilasius) nests on the ground beside commonly traveled roads. It adds the nests in boasts by Osprey (Pandion haliaetus) and Saker Falcon's (Falco cherrug) nests in attics. It stresses that these odd behaviors have the potential in unveiling the plasticity of a species' behavioral repertoire.