Subject: Owl Conservation and Research News -- 3 July 2021

Owl Conservation & Research News
A summary of recent owl publications, conservation and conference and news.
Card, E., Check, C. and Boyce, A.J., 2020. Rediscovery of Rajah Scops-Owl (Otus brookii brookii) on the island of Borneo. The Wilson Journal of Ornithology, 132(3), pp.769-773.
The Bornean subspecies of Rajah Scops-Owl (Otus brookii brookii) has not been documented alive in the wild since its discovery in 1892 and there are no photographs of the bird in life. We report the rediscovery of this subspecies in the montane forests of Mount Kinabalu (Sabah, Malaysia) at an elevation of 1,650 m and provide the first photographs of this subspecies in the wild. Almost all basic elements of this species' ecology remain unknown, including vocalizations, distribution, breeding biology, and population size. Additionally, phylogeographic patterns of montane birds in Borneo and Sumatra, as well as plumage characters, suggest that O. b. brookii may be deserving of species classification. However, the rarity of O. b. brookii has made quantitative phylogenetic analysis impossible. Properly resolving the ecology, distribution, and taxonomic standing of O. b. brookii could have important conservation implications.
Slankard, K.G., Patton, M.D., Taylor, L.F. and Barnard, J.O., 2021. Two Case Studies of Satellite Tracking Juvenile Barn Owl (Tyto alba) Dispersal. Journal of Raptor Research, 55(1), pp.115-118.
The Barn Owl is a species of conservation concern in Kentucky and elsewhere in the Midwestern United States. However, research on the dispersal, movements and survival of Barn Owls in the US is lacking. For this study, we used a 20 g Argos transmitter to monitor the movements of two recently fledged Barn Owls during 2014 and 2015. Movement patterns, including direction and speed varied between the two individuals. Minimum distance travelled ranged from 178-324 km and final distance from natal site ranged from 23.5-139 km. The maximum rate of movement during dispersal ranged from 30.1-64.0 km/8-hr tracking period with an average rate of 6.4-6.8 km/8-hr tracking period.
Click here for the full-text article.
Clément, M., Shonfield, J., Bayne, E.M., Baldwin, R. and Barrett, K., 2021. Quantifying Vocal Activity and Detection Probability to Inform Survey Methods for Barred Owls (Strix varia). Journal of Raptor Research, 55(1), pp.45-55.
Owls can be difficult to detect due to their secretive behavior, typically low calling rate, and low density on the landscape. Low detection probability during surveys can result in an underestimation of the presence and abundance of a species. Thus, optimizing detection probability of surveys targeting owls is necessary to accurately address ecological questions. We used datasets collected in South Carolina, USA, and Alberta, Canada, to investigate how survey detection can be optimized for Barred Owls (Strix varia). We examined seasonal effects on the detection probability of Barred Owls as determined by playback surveys and autonomous recording unit (ARU) surveys, and whether daily patterns of Barred Owl vocal activity could be used to improve the efficiency of ARU surveys. For each survey method, we estimated the number of survey days needed to obtain a seasonal detection probability ≥ 90% of Barred Owls. We found detection probability with playbacks increased as the breeding season progressed. The effect of seasonality on detection probability with ARUs was dependent on the way encounter history was defined. Barred Owl vocal activity peaked twice per night, with one vocalization peak occurring immediately after sunset and another 7–9 hr after sunset. By targeting these vocalization peaks during surveys, we found that we could reduce ARU survey time by 50% and still retain .82% of the original site detections, thereby reducing survey processing time. Although playback surveys were more efficient than ARU surveys at detecting Barred Owls, ARUs have numerous advantages, such as reducing survey effort and disturbance to the target animal. Ultimately, survey designs are dictated by the budget, personnel capacity, study region, and research objectives, but our findings will help researchers plan studies that optimize detection probability and minimize survey cost and effort.
Reynolds, M., Shook, J., Breed, G. and Kielland, K., 2021. Detection and Density of the Great Horned Owl (Bubo virginianus) in Arctic Alaska. Journal of Raptor Research, 55(1), pp.56-64.
Audio playback of vocalizations by conspecifics is commonly used to elicit calls when surveying birds of prey. Methods for call surveys vary widely in their use of silent listening periods, and usually range from 3–15 min in length. We aimed to refine this approach for detecting Great Horned Owls (Bubo virginianus) in Arctic Alaska, which is the northernmost limit of their breeding range. We used two playback protocols: protocol 1 entailed uninterrupted playback, whereas protocol 2 interspersed silent listening periods with playback during 12-min surveys. In playback surveys consisting of 166 point counts during the 2017 and 2018 breeding seasons, the probability of detecting a Great Horned Owl was 0.46 (95% CI ¼ 60.09) with protocol 1 and 0.35 (95% CI ¼ 60.12) with protocol 2 (P ¼ 0.18). The probability of detection rose with the length of the playback: of all owls detected during the 12-min surveys, 23% (95% CI ¼ 66.4%) responded within the first 3 min, 52 6 7.6% within the first 6 min, and 80 6 6.1% within 9 min. Including silent listening periods was not necessary for detecting Great Horned Owls during call surveys. We found no correlation between probability of detection and either cloud cover or wind speed (P ¼ 0.60 and P ¼ 0.28, respectively). However, we found a negative correlation between temperature and probability of detection (P ¼ 0.02). From these surveys, we calculated the density of Great Horned Owls in the Middle Fork Koyukuk Valley, Alaska (approximately 67.589°N, 149.789°W) was 4.2 6 2.6 owls/km2 during the winters of 2017 and 2018, which represents the first estimate of density at the northern breeding limit of the species.
Deshler, J.F., 2020. Higher reversed sexual size dimorphism among nesting pairs of Northern Pygmy-Owls (Glaucidium gnoma) in northwestern Oregon than among specimens collected at the range-wide scale. The Wilson Journal of Ornithology, 132(3), pp.619-627.
I report on the strength of reversed sexual size dimorphism (RSD) in a local sub-population of Northern Pygmy-Owls (Glaucidium gnoma) in northwestern Oregon (2007–2012) in comparison to range-wide museum specimens examined by Earhart and Johnson (1970). Using Storer's Dimorphism Index (DI), RSD was higher among local breeding pairs (DImass = 6.64, DIwing = 4.90, n = 20 pairs) and among all local specimens (DImass = 6.20, DIwing = 4.39, n = 31 females, n= 23 males) than for specimens range-wide (DImass = 5.45, DIwing = 4.30, n= 10 females, n= 42 males). RSD was also more distinct locally, because mass alone was diagnostic of the sexes at a threshold of 69 g and wing chord was nearly diagnostic, whereas range-wide there was greater intrasexual variation and intersexual overlap in both metrics. Locally, females weighed 75.3 ± 5.6 g (range 69.0–94.2 g), and males weighed 62.5 ± 2.5 g (range 58.5–68.5 g); all local males had wing chords <92 mm (89.2 ± 2.0 mm; range 85.0–91.5 mm), whereas for 90% of females wing chord was ≥92 mm (93.2 ± 1.3 mm; range 89.0–96.0 mm). Clutch size (F1,4 = 1.822, P= 0.248, n= 20) and the number of fledged young (F1,8 = 0.00, P= 0.619, n= 19) were independent of RSD among local breeding pairs. Vertebrate prey composition shifted seasonally and was similar at the 2 scales, with agile avian prey taken most frequently during the breeding season, when the evolutionary consequences of diet on RSD matter most. I found intersexual variation in prey composition at the local scale where males took avian prey more frequently than females. I concluded that RSD in pygmy-owls was stronger at the local scale and that intersexual differences in prey composition may be related to RSD in this species. This study highlights the value of examining multiple scales and seasonal variation in prey composition when evaluating the merits of RSD hypotheses. It also contributes to our understanding of one of the least studied owls in North America.
Deshler, J.F., 2020. Northern Pygmy-Owl (Glaucidium gnoma) nesting ecology in northwestern Oregon. The Wilson Journal of Ornithology 132(2), pp.352-365. 
I report on the nesting ecology of the Northern Pygmy-Owl (Glaucidium gnoma) in northwestern Oregon based on 71 breeding attempts, including observations at 66 nest cavities during 12 years of study (2007–2013, 2016–2020). I focus on the annual shift in the start of laying and in productivity (clutch size) in relation to prey composition. For all years combined, the start of laying spanned 2 months (27 Mar–30 May). The mean annual start of laying varied across consecutive years by nearly 3 weeks (19.0 ± 6.5 d); mean productivity at nests varied annually by 23% (1.2 ± 0.5 eggs). Observed clutch size was most frequently 5 or 6 eggs (5.6 ± 0.9, range 4–8 eggs, n = 47), but most clutches in early-nesting years were 6 or 7 eggs, and 4 or 5 eggs in late-nesting years. The mean incubation and nestling periods were 29.4 ± 1.1 d and 26.4 ± 1.2 d, respectively. Pygmy-owls fledged a mean of 5.1 ± 1.1 young at 58 successful nests and 4.2 ± 2.2 for all breeding attempts. Vertebrate prey composition varied annually and seasonally. Pygmy-owls took mammalian prey more often early in the breeding season (66% of vertebrate prey) and in early-nesting years (65%); avian prey were more frequently taken late in the breeding season (66%) and in late-nesting years (66%). Pygmy-owls nested disproportionately in coniferous trees (χ2 = 67.48, P < 0.001, df = 1, n = 66); nests in western redcedars (Thuja plicata) fledged 1.5 more owlets and failed less often (5% failed) than nests in other tree species (22% failed). Observations at this largest ever collection of Northern Pygmy-Owl nests reveal a commitment by these small owls (1) to produce young annually, even when they had to overcome obstacles such as mate procurement, mate loss, and nest depredation, and (2) to use mammalian prey to increase productivity in some years.
Pérez-Granados, C., Schuchmann, K-L, and Marques, M.I., 2021. Vocal activity of the Ferruginous pygmy-owl (Glaucidium brasilianum) is strongly correlated with moon phase and nocturnal temperature. Ethology Ecology & Evolution, 33(1), pp.62-72.
Bird vocal activity is affected by endogenous and exogenous factors. Owl surveys are mainly based on the detection of nocturnal calls, and therefore, the impact of exogenous factors on owls’ vocal activity may have consequences in conservation planning and behavioural studies. However, our current knowledge about the impact of climatic factors and the moon phase on owl calling behaviour is very limited, especially in the Neotropics. We used autonomous recording units to evaluate the effect of air temperature, rainfall, relative air humidity, and percent of the moon illuminated on the vocal occurrence (active/inactive) of the Ferruginous pygmy-owl (Glaucidium brasilianum) over three consecutive moon cycles in the Brazilian Pantanal. Vocal activity was positively associated with the percent of the moon illuminated, with 75% of the nights on which the species was vocally active having a moon illumination percentage higher than 77%. The vocal activity of the species was negatively associated with the nocturnal air temperature, with more vocal activity observed on cooler nights. Relative air humidity and daily rainfall were not associated with the vocal activity of the Ferruginous pygmy-owl. Our study improves the knowledge about the impact of exogenous factors on the calling behaviour of Neotropical owls. We conclude that future surveys aiming to detect the Ferruginous pygmy-owl should be carried out on nights with a high percent of moon illumination (>75%) and nights with low average temperature (< 18 °C).
Pérez-Granados, C., Schuchmann, K-L, and Marques, M.I., 2021. Passive acoustic monitoring of the Ferruginous Pygmy-Owl (Glaucidium brasilianum) over a complete annual cycle: seasonality and monitoring recommendations, Studies on Neotropical Fauna and Environment, pp.1-8.
Monitoring the vocal behavior of owls is challenging because of their nocturnal habits and limited vocal activity. Here, we evaluated the use of passive acoustic monitoring coupled with automated signal recognition software to monitor the spontaneous vocal activity of the Ferruginous Pygmy-Owl (Glaucidium brasilianum) over a complete annual cycle at five recording stations in the Brazilian Pantanal. The vocal behavior of this species was concentrated during the crepuscular periods, with highest vocal activity in the hours prior to sunrise. The Ferruginous Pygmy-Owl was vocally active throughout the year, but the species showed a peak of activity from June to August. Paired Ferruginous Pygmy-Owl males tend to perform territorial calls less often during the nestling period, which may partly explain the significant decrease in the vocal activity after August. Our results suggest that the breeding period of the species starts in June, and the nesting phase probably occurs from September onwards, when the wet season starts. The first rains in seasonal tropical areas are usually associated with an increase in food availability, which may explain the species´ breeding period onset. Future surveys aiming to monitor the species, avoiding the use of broadcast calls, should be performed before sunrise between June and August, when the vocal activity was maximal.
Click here for the full-text article.
Iudica, C.A., Andrade, L.F. and Sheffield, S.R., 2021. Galapagos Short-Eared Owl (Asio Flammeus Galapagoensis) Preying Upon a Marine Iguana (Amblyrhynchus Cristatus) on Isla Isabela, Galapagos Islands, Ecuador. Journal of Raptor Research, 55(1), pp.124-126.
The short-eared owl is one of the most widely distributed owl species in the world. Prey selection by short-eared owls has been studied extensively across its Holarctic range, and dietary preferences are well known. Small mammals make up a vast majority of prey items throughout its range. Birds are taken on occasion, but mainly in low numbers except in coastal locations or other areas where birds tend to be numerous and mammalian prey may be scarce. Overall, there are almost no records of short-eared owls taking reptilian species as prey. This paper reports a notable record of a Galapagos Is short-eared owl preying on and consuming an immature marine iguana (Amblyrhynchus cristatus). The observation occurred on Isla Isabela, Galapagos Is, Ecuador.
Prey selection for this owl could have been influenced by a strong invasive species (rodent) control program in place in this area of the island, and also by lack of competition from barn owls and Galapagos hawks. However, Galapagos Is short-eared owls may have been predating young marine iguanas for some time now without being reported. Galapagos Is short-eared owls have a varied, opportunistic diet across the Galapagos archipelago.
Click here for the full-text article.
Wall, J., Brinker, D., Weidensaul, S., Okines, D., Côté, P. and Therrien, J.F., 2020. Twenty-five year population trends in Northern Saw-whet Owl (Aegolius acadicus) in eastern North America. The Wilson Journal of Ornithology, 132(3), pp.739-745.
Due to the low detectability of Northern Saw-whet Owls (Aegolius acadicus; hereafter, NSWO) throughout their annual cycle, standardized monitoring during migration allows for population assessments over time. We assessed age-class population trends in NSWO throughout eastern North America using banding data from 7 sites over a 25 year period. Using a mixed linear model, we did not detect any significant trends over time for the total owl count, adult owl count, and juvenile owl count from 1992 to 2017. During the period when all 7 sites were active from 2001 to 2017, trend estimates remained nonsignificant despite showing negative slopes. We confirmed this nonsignificant, negative trend through a similar mixed linear model of NSWO data from Christmas Bird Counts. Our results suggest that NSWO populations across eastern North America have been relatively stable since 1992 throughout their migration and winter ranges and demonstrate the value of standardized banding data for monitoring the regional population status of NSWO.
Seeking World Owl Hall of Fame Nominations
The World Owl Hall of Fame is seeking nominations of individuals who have done exceptional things to help make the world a better place for owls. Nominations are due August 31, 2021. A panel of judges from around the world selects the winners, and awards will be presented at the International Festival of Owls on March 5, 2022 in Houston, Minnesota USA.
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