Subject: Owl Conservation and Research News -- 9 February 2021

Owl Conservation & Research News
A summary of recent owl publications, plus conservation and conference news.

Note: Submissions are edited for length, but not necessarily for grammar. Citations come from various journals and no effort has been made to standardize them.
Miller, R. A. (2020, December 21). Project WAfLS 2020 and Comprehensive Results. Retrieved January 08, 2021, from
Project WAfLS is an eight-state program designed to assess the population status, trends, and threats against the Short-eared Owl in the western United States. Project WAfLS engages enthusiastic citizen-scientist volunteers to gather critical survey data, enabling a rigorous assessment of the status of this species.
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Mayr, G., P. D. Giingerich, and T. Smith. 2020. Skeleton of a new owl from the early Eocene of North America (Aves, Strigiformes) with an accipitrid-like foot morphology. Journal of Vertebrate Paleontology:DOI: 10.1080/02724634.2020.1769116.
We describe a partial skeleton of a large-sized owl from Wasatchian strata of the Willwood Formation (Wyoming, U.S.A.). The holotype of Primoptynx poliotauros, gen. et sp. nov., includes all major postcranial bones and is one of the most substantial Paleogene records of the Strigiformes. The fossil shows that owls exhibited a considerable morphological diversity in the early Eocene of North America and occupied disparate ecological niches. As in the protostrigid taxon Minerva from the late early to early middle Eocene of North America, but unlike in extant owls, the ungual phalanges of the hallux and the second toe of the new species are distinctly larger than those of the other toes. Primoptynx poliotauros gen. et sp. nov., however, does not exhibit the derived tibiotarsus morphology of the Protostrigidae. Even though the new species may well be a stem group representative of protostrigid owls, current data do not allow an unambiguous phylogenetic placement. Concerning the size of the ungual phalanges, the feet of P. poliotauros correspond to those of extant hawks and allies (Accipitridae). We therefore hypothesize that it used its feet to dispatch prey items in a hawk-like manner, whereas extant owls kill prey with their beak. Primoptynx and protostrigid owls were possibly specialized in foraging on prey items that required an accipitrid-like killing strategy, such as larger-sized or more defensive mammals. The extinction of these peculiar owls may have been related to the radiation of accipitrid diurnal birds of prey, which appear to have diversified in the late Eocene and early Oligocene.
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Mueller, J. C., M. Carrete, S. Boerno, H. Kuhl, J. L. Tella, and B. Kempenaers. 2020. Genes acting in synapses and neuron projections are early targets of selection during urban colonization. Molecular Ecology: (accepted articles).
When a species colonizes an urban habitat, differences in the environment can create novel selection pressures. Successful colonization will further lead to demographic perturbations and genetic drift, which can interfere with selection. Here, we test for consistent urban selection signals in multiple populations of the burrowing owl (Athene cunicularia), a species that colonized South American cities just a few decades ago. We sequenced 213 owls from three urban‐rural population pairs and performed a genome‐wide comparison of urban against rural birds. We further studied genome‐wide associations with flight initiation distance (FID), a measure of harm avoidance in which urban and rural birds are known to differ. Based on four samples taken over nine years from one of the urban populations, we investigated temporal allele frequency changes. The genomic data were also used to identify urban‐specific signatures of selective sweeps. Single genomic sites did not reach genome‐wide significance for any association. However, a gene‐set analysis on the strongest signals from these four selection scans suggests a significant enrichment of genes with known functions related to synapses and neuron projections. We identified 98 genes predominantly expressed in the brain, of which many may play a role in the modulation of brain connectivity and consequently in cognitive function and motivational behavior during urbanization. Furthermore, polymorphisms in the promotor region of the synaptic SERT gene – one of the two candidates known to correlate with urban colonization in birds ‐ associated with the habitat in which individuals lived (urban vs. rural).
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Schofield, L. N., S. A. Eyes, R. B. Siegel, and S. L. Stock. 2020. Habitat selection by spotted owls after a megafire in Yosemite National Park. Forest Ecology and Management 478:art. no. 118511.
As fires in the western United States have become larger and more severe over recent decades, understanding how the changing fire regime affects wildlife has become a key issue for conservation. Spotted owls (Strix occidentalis) associate with late-successional forest characteristics and therefore may be particularly sensitive to structural changes in habitat that result from fire. Previous studies have found varying responses of the owls to forest fire. We investigated the effects of the 2013 Rim Fire on territory selection by California spotted owls within Yosemite National Park, which, unlike the surrounding landscape, has been managed with no commercial logging since the early 1900s and minimal fire suppression since the 1970s. We examined specific habitat characteristics associated with spotted owl presence before and after the fire to understand how fire-induced changes in habitat structure may influence spotted owl territory selection. Spotted owls persisted and nested within the fire perimeter throughout the four post-fire years of our study at rates similar to what we observed in areas of Yosemite that were unaffected by the fire. However, within the fire perimeter, spotted owls avoided areas characterized by >30% percent high severity fire. Prior to the fire, spotted owls selected for areas of high canopy cover relative to the rest of the landscape; after the fire, even though territory centers shifted substantially from pre-fire locations, pre-fire canopy cover remained a stronger predictor of spotted owl presence than post-fire canopy cover, or any other pre- or post-fire habitat variables we assessed. The importance of pre-fire forest structure in predicting owl presence after fire suggests that reported variation in spotted owl population response to different fires across the Sierra Nevada may in part reflect variation in pre-fire forest characteristics, and perhaps different forest management regimes that shaped those characteristics. Pre-fire forest characteristics may impart a legacy of post-fire habitat conditions important to owls that commonly used forest and fire metrics do not effectively describe. Further study of owl response to fire in forests with a broader spectrum of pre-fire forest structure and management regimes is needed to better predict and manage effects of the changing fire regime on spotted owls.
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Zuberogoitia, I., G. Burgos, J. A. González-Oreja, J. E. Martinez, J. Morant, and J. Zabala. 2020. Testing detectability of radio-tracked Tawny Owls using playback broadcast surveys: designing evidence-based surveys. Ardeola 67(2):355-369.
Owls, like other secretive species, are difficult to detect. During the last few decades, protocols used for surveying owls have revealed the best methods to acquire accurate data about their distribution and abundance. However, these protocols were established by testing the response of owls to playback of broadcast calls, using wild, unknown individuals that were only noticeable when vocalisations were given/detected. Therefore, there is no clear consensus on the best method to survey owls. We tested a protocol to survey Tawny Owls Strix aluco using 20 radio-tracked individuals in two study areas with contrasting owl density. We conducted 58 survey tests during winter 2014-2015. In the two study areas respectively, 61.3% and 70.4% of the target individuals responded, on average, within the first six minutes after the start of call playback. Naïve occupancy estimates were 67.7% and 85.2%, respectively, considering the combined responses of the target individual and its mate. We detected a movement of the target owls from their original position towards the playback source on 72.4% of the sampling occasions in both areas. Tawny Owls approached within 50m of the playback point on only 56.9% of occasions. Mates or neighbours responded to broadcast calls more often in the high-density area than in the low density one. The detection probability of target owls increased more than fourfold when their mates joined in defence of the territory, and also increased fourfold when the target individuals approached the broadcast point and when we increased the playback period from five to fifteen minutes. We recommend two 15-minute periods of call playback per point and year, on dry and calm winter nights, at survey points one kilometre apart.
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Kulkarni, J., and P. Mehta. 2020. Habitat selectivity by the Forest Owlet Athene blewitti in Nandurbar District, Maharashtra, India. Indian Birds 16(2):33-39.
The Forest Owlet Athene (Heteroglaux) blewitti is an endangered owl species found in isolated populations in India. Toranmal and Taloda forests in Nandurbar District, located in north-western Maharashtra, are type localities of the Forest Owlet, from where it has been reported since 1872, and was rediscovered in 1997. During 2016–2017, we carried out an intensive survey for the Forest Owlet, in Nandurbar District, to reassess its distribution and habitat preferences. Our study reports that the Forest Owlet prefers a habitat that is semi-open, teak-bearing dry deciduous forest interspersed with agricultural fields. However, it is an obligate forest species, and is not found in non-forest habitats like agriculture and human habitation. It prefers patchy rather than continuous forest. It prefers forests with less bamboo. It is adapted to living in hilly terrain and prefers valleys, hill slopes, and plateaus, and avoids hilltops. It is found at elevations from 250 to 550 m. It avoids areas with high levels of illegal tree cutting. Our study found that the degradation of forest in Nandurbar District is a serious threat to the survival of the Forest Owlet in the district.
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Irwin, L. L., D. R. Rock, S. C. Rock, A. K. Heyerly, and L. A. Clark. 2020. Barred Owl effects on Spotted Owl resource selection: a meta-analysis. Journal of Wildlife Management 84(1):96-117.
We quantified the effects of barred owls (Strix varia) on fine-scale (~2 ha), spatially explicit selection of putative foraging habitat by 175 radio-tagged northern spotted owls (Strix occidentalis caurina) from 1998 to 2012 in western Oregon and northern California, USA. We constructed annual nighttime discrete-choice resource selection functions (RSFs) for northern spotted owls in 8 study areas. We compared RSFs from pooled data from 4 study areas where barred owls were absent or rare (≤14% of spotted owl territories potentially influenced by barred owls) with RSFs from 4 study areas where barred owls were abundant (≥89% of spotted owl territories potentially influenced by barred owls), and we conducted a meta-analysis of all 8 study areas. Top-ranked RSFs for individual study areas indicated that the relative probability a forest patch was selected by northern spotted owls for foraging was most strongly associated with basal area of large coniferous trees (≥66 cm diameter at breast height [dbh]) or quadratic mean diameter (QMD, the diameter of trees of average basal area) of all coniferous trees. The influence of such trees was non‐linear, usually quadratic, in 7 study areas, suggesting that an optimal basal area of large‐diameter trees or QMD may be associated with selection of foraging patches. The relative probability of selection of such trees decreased nonlinearly with increasing distance from nest sites in ≥4 study areas. Basal area of all or specific hardwood tree species was linearly associated with increases in the relative probability of a patch being used for foraging in 7 of 8 study areas. The relative probability of selection was also positively associated with densities of large snags (>50 cm dbh), coarse woody debris, and undergrowth shrubs in most study areas where we estimated those covariates. The relative probability that a patch was selected decreased nonlinearly with increasing distance from streams (7 study areas), increasing elevation (5 study areas), and decreasing slope (5 study areas). Barred owls exerted strong effects on habitat selection by spotted owls, which may have attempted to minimize interference competition via spatial segregation. Spotted owls occupying study areas where barred owls were abundant used foraging patches at greater distances from streams, at greater distances from nest sites, and on steeper and warmer slopes than those occupying areas with few or no barred owls. In addition, northern spotted owls in areas where barred owls were abundant exhibited reduced selection for large‐diameter trees close to nest sites but may have compensated by increasing use of large trees in home-range locations distant from nest sites. Programs that seek to improve the link between spotted owl demographic performance or occupancy rate and habitat conditions should account for the influences of fine-scale variation in vegetation composition and structure and physiographic conditions. Forest managers may contribute to spotted owl conservation via silvicultural prescriptions that retain coarse woody debris and large snags, promote undergrowth shrubs, and retain intermediate to high densities of large, old shade-intolerant early-seral trees and riparian hardwoods within and beyond core areas surrounding nest sites.
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Jones, G. M., H. A. Kramer, S. A. Whitmore, W. J. Berigan, D. J. Tempel, C. M. Wood, B. K. Hobart, T. Erker, F. A. Atuo, N. F. Pietrunti, R. G. Kelsey, R. J. Gutiérrez, and M. Z. Pery. 2020. Habitat selection by spotted owls after a megafire reflects their adaptation to historical frequent-fire regimes. Landscape Ecology 35:1199-1213.
Climate and land-use change have led to disturbance regimes in many ecosystems without a historical analog, leading to uncertainty about how species adapted to past conditions will respond to novel post-disturbance landscapes. We examined habitat selection by spotted owls in a post-fire landscape. We tested whether selection or avoidance of severely burned areas could be explained by patch size or configuration, and whether variation in selection among individuals could be explained by differences in habitat availability. We applied mixed-effects models to GPS data from 20 spotted owls in the Sierra Nevada, California, USA, with individual owls occupying home ranges spanning a broad range of post-fire conditions after the 2014 King Fire. Individual spotted owls whose home ranges experienced less severe fire (< 5% of home range severely burned) tended to select severely burned forest, but owls avoided severely burned forest when more of their home range was affected (~ 5–40%). Owls also tended to select severe fire patches that were smaller in size and more complex in shape, and rarely traveled > 100-m into severe fire patches. Spotted owls avoided areas that had experienced post-fire salvage logging but the interpretation of this effect was nuanced. Owls also avoided areas that were classified as open and/or young forest prior to the fire. Our results support the hypothesis that spotted owls are adapted to historical fire regimes characterized by small severe fire patches in this region. Shifts in disturbance regimes that produce novel landscape patterns characterized by large, homogeneous patches of high-severity fire may negatively affect this species.
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Luna, A., A. Palma, A. Sanz-Aguilar, T. J. L, and M. Carrete. 2020. Sex, personality and conspecific density influence natal dispersal with lifetime fitness consequences in urban and rural burrowing owls. PLoS ONE 15(2):e0226089.
There is a growing need to understand how species respond to habitat changes and the potential key role played by natal dispersal in population dynamics, structure and gene flow. However, few studies have explored differences in this process between conspecifics living in natural habitats and those inhabiting landscapes highly transformed by humans, such as cities. Here, we investigate how individual traits and social characteristics can influence the natal dispersal decisions of burrowing owls (Athene cunicularia) living in urban and rural areas, as well as the consequences in terms of reproductive success and apparent survival. We found short dispersal movements among individuals, with differences between urban and rural birds (i.e., the former covering shorter distances than the latter), maybe because of the higher conspecific density of urban compared to rural areas. Moreover, we found that urban and rural females as well as bold individuals (i.e., individuals with shorter flight initiation distance) exhibited longer dispersal distances than their counterparts. These dispersal decisions have effects on individual fitness. Individuals traveling longer distances increased their reproductive prospects (productivity during the first breeding attempt, and long term productivity). However, the apparent survival of females decreased when they dispersed farther from their natal territory. Although further research is needed to properly understand the ecological and evolutionary consequences of dispersal patterns in transformed habitats, our results provide information about the drivers and the consequences of the restricted natal movements of this species, which may explain its population structuring through restricted gene flow between and within urban and rural areas.
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Macías-Duarte, A., C. J. Conway, and M. Culver. 2020. Agriculture creates subtle genetic structure among migratory and nonmigratory populations of burrowing owls throughout North America. Ecology and Evolution DOI: 10.1002/ece3.6725.
Population structure across a species distribution primarily reflects historical, ecological, and evolutionary processes. However, large-scale contemporaneous changes in land use have the potential to create changes in habitat quality and thereby cause changes in gene flow, population structure, and distributions. As such, land-use changes in one portion of a species range may explain declines in other portions of their range. For example, many burrowing owl populations have declined or become extirpated near the northern edge of the species' breeding distribution during the second half of the 20th century. In the same period, large extensions of thornscrub were converted to irrigated agriculture in northwestern Mexico. These irrigated areas may now support the highest densities of burrowing owls in North America. We tested the hypothesis that burrowing owls that colonized this recently created owl habitat in northwestern Mexico originated from declining migratory populations from the northern portion of the species' range (migration-driven breeding dispersal whereby long-distance migrants from Canada and the United States became year-round residents in the newly created irrigated agriculture areas in Mexico). We used 10 novel microsatellite markers to genotype 1,560 owls from 36 study locations in Canada, Mexico, and the United States. We found that burrowing owl populations are practically panmictic throughout the entire North American breeding range. However, an analysis of molecular variance provided some evidence that burrowing owl populations in northwestern Mexico and Canada together are more genetically differentiated from the rest of the populations in the breeding range, lending some support to our migration-driven breeding dispersal hypothesis. We found evidence of subtle genetic differentiation associated with irrigated agricultural areas in southern Sonora and Sinaloa in northwestern Mexico. Our results suggest that land use can produce location-specific population dynamics leading to subtle genetic structure even in the absence of dispersal barriers.
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Olsen, J., S. Debus, S. Trost, L. Tsang, and H. Parnaby. 2020. Some vertebrate prey of Barn Owls Tyto alba sumbaensis on Sumba and Rote, Indonesia. Australian Field Ornithology 37:44-47.
The diet of the Barn Owl Tyto alba sumbaensis is little known in Wallacea. Samples of pellets from nests in a church in an urban setting on Sumba and in a forested, limestone cliff setting near Nembrala (Nemberala) on the small island of Rote (Roti), off Timor, were collected in July 2001 and July 2002, respectively. The Sumba sample contained the remains of rodents (three Black Rats Rattus rattus, four Pacific Rats R. exulans and one probable House Mouse Mus musculus) and birds (17 Eurasian Tree Sparrows Passer montanus). The sample from Rote contained the remains of 30 small fruit-bats (24 Geoffroy’s Rousettes Rousettus amplexicaudatus and six that were probably also this species).
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Potier, S., M. Mitkus, and A. Kelber. 2020. Visual adaptations of diurnal and nocturnal raptors. Seminars in Cell and Developmental Biology:DOI:
Raptors have always fascinated mankind, owls for their highly sensitive vision, and eagles for their high visual acuity. We summarize what is presently known about the eyes as well as the visual abilities of these birds, and point out knowledge gaps. We discuss visual fields, eye movements, accommodation, ocular media transmittance, spectral sensitivity, retinal anatomy and what is known about visual pathways. The specific adaptations of owls to dim-light vision include large corneal diameters compared to axial (and focal) length, a rod-dominated retina and low spatial and temporal resolution of vision. Adaptations of diurnal raptors to high acuity vision in bright light include rod- and double cone-free foveae, high cone and retinal ganglion cell densities and high temporal resolution. We point out that more studies, preferably using behavioural and non-invasive methods, are desirable.
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