Owl Calls Research Articles

Antipredator responses of bats during short boreal nights with variable climatic conditions

Abstract The threat of predation can influence the behavior of animals. To minimize the impact of predation, animals rely on antipredatory responses and effectively balance these responses with other activities to maximize survival. Boreal bats are nocturnal animals that must forage within a narrow time frame during short, light summer nights with unpredictable weather. Despite having no specialized predators, boreal bats are still subject to predation. However, whether they express antipredatory responses has not been established. We studied antipredatory responses and responses to climatic conditions in boreal bats in 2 settings: 1) during roost emergence; and 2) during foraging within Tawny Owl territories and at locations with no Tawny Owl sightings. Acoustic data were collected at 23 roosts and 10 foraging grounds. Two controlled predation threats were used—playbacks of Tawny Owl calls and fledgling calls. Fledgling calls were only played during roost emergence. In both experiments, music and no treatment were used as controls. We also incorporated weather variables in the model. According to our results, bats tend to delay their emergence by 16 min when Tawny Owl calls were played outside the roost, but this effect was not noticeable when weather variables were included. There was no difference in exit time when music or fledgling sounds were played. While foraging, bats reduced their activity in Tawny Owl territories when calls of owls or music were played compared to no treatment. These results suggest that bats might display variable antipredatory responses, but weather influences behavior of bats more than predation risk, highlighting the importance of energy-saving strategies at northerly latitudes.

Functional neurogenomic responses to acoustic threats, including a heterospecific referential alarm call and its referent, in the auditory forebrain of red-winged blackbirds

In animal communication, functionally referential alarm calls elicit the same behavioral responses as their referents, despite their typically distinct bioacoustic traits. Yet the auditory forebrain in at least one songbird species, the black-capped chickadee Poecile atricapillus, responds similarly to threat calls and their referent predatory owl calls, as assessed by immediate early gene responses in the secondary auditory forebrain nuclei. Whether and where in the brain such perceptual and cognitive equivalence is processed remains to be understood in most other avian systems. Here, we studied the functional neurogenomic (non-) equivalence of acoustic threat stimuli perception by the red-winged blackbird Agelaius phoeniceus in response to the actual calls of the obligate brood parasitic brown-headed cowbird Molothrus ater and the referential anti-parasitic alarm calls of the yellow warbler Setophaga petechia, upon which the blackbird is known to eavesdrop. Using RNA-sequencing from neural tissue in the auditory lobule (primary and secondary auditory nuclei combined), in contrast to previous findings, we found significant differences in the gene expression profiles of both an immediate early gene, ZENK (egr-1), and other song-system relevant gene-products in blackbirds responding to cowbird vs. warbler calls. In turn, direct cues of threats (including conspecific intruder calls and nest-predator calls) elicited higher ZENK and other differential gene expression patterns compared to harmless heterospecific calls. These patterns are consistent with a perceptual non-equivalence in the auditory forebrain of adult male red-winged blackbirds in response to referential calls and the calls of their referents.

Using passive acoustic monitoring to estimate northern spotted owl landscape use and pair occupancy

AbstractManaging forests for biodiversity conservation while maintaining economic output is a major challenge globally and requires accurate and timely monitoring of imperiled species. In the Pacific Northwest, USA, forest management is heavily influenced by the status of northern spotted owls (Strix occidentalis caurina), which have been in continued population decline for the past four decades. The monitoring program for northern spotted owls is transitioning from mark–resight surveys to a passive acoustic framework, requiring development of alternative analysis approaches. To maintain relevance for conservation and management, these analyses must accurately track underlying population changes, identify responses to disturbance, and estimate occupancy of owl pairs. We randomly selected and surveyed 5‐km2 hexagons for 6 weeks using passive acoustic monitoring in the Olympic Peninsula of Washington and the Oregon Coast Range during the 2018 spotted owl breeding season. We used a convolutional neural network to identify spotted owl calls, followed by logistic regression to determine the sex of vocalizing owls to assign pair status. We implemented multistate occupancy models to estimate probabilities of detection, species‐level landscape use, and pair occupancy of spotted owls. We also quantified detections of barred owls (Strix varia), a congeneric competitor and important driver of spotted owl population declines. The overall rate of hexagon use by spotted owls was estimated at 0.21 (SD 0.04) after adjusting for imperfect detection, and pair occupancy was 0.07 (SD 0.02). The probability of detecting a pair (i.e., both female and male) during a weekly occasion was relatively low (0.03, SD 0.01), indicating that true pair occupancy was between 1.3 and 4.1 times greater than the proportion of hexagons with observed pair detections. Barred owls were ubiquitous, with a naïve occupancy rate of 0.97. The intensity of calling by barred owls had a weak, negative effect on the probability of spotted owls being paired when present but had little measurable effect on their detectability. This work establishes a framework that may be effective for spotted owl population monitoring and illustrates that pairs have very low detection probability, which—combined with increasingly low numbers of spotted owl pairs—is an important consideration for conservation and management.

Distinguishing Sex of Northern Spotted Owls with Passive Acoustic Monitoring

ABSTRACT Northern Spotted Owls (Strix occidentalis caurina) are of management and conservation concern in the US Pacific Northwest where populations have been monitored since the 1990s using mark-resight methods. Passive acoustic monitoring has the potential to support monitoring efforts; however, its use is currently primarily restricted to determining species presence rather than breeding status. Distinguishing female from male Northern Spotted Owl vocalizations could facilitate determination of pair status using passive acoustic methods, greatly enhancing inference derived from noninvasive monitoring data. In 2017, we deployed 150 autonomous recording units (ARUs) within 30 5-km2 hexagons overlapping recently occupied owl territories in Oregon and Washington, USA, where mark-resight methods were simultaneously occurring. We collected approximately 150,000 hours of recordings and detected 22,458 Northern Spotted Owl vocalizations at 76 ARUs. We summarized vocalizations by call type and found differences in the proportion of call types made by single, paired, and nesting owls. We used expert opinion to classify 2812 four-note location calls as female or male. We summarized inter-sex variation within 19 acoustic attributes of the four-note location call and its subcomponents, and developed a mixed logistic regression model to classify sex based on call-segment acoustic attributes. Males generally called at lower frequencies than females, with mean fundamental frequencies of 556 Hz and 666 Hz, respectively. Male four-note location calls were also longer than female calls, with signal median times of 1.99 s and 1.71 s, respectively. The middle-two-note and the full-call segment of the four-note location call were both useful for classifying sex of the calling owl. Our top-ranked models were able to predict 82–83% of our testing data consistent with expert classification as either male or female with 98–99% accuracy (17–18% of test set was classified as unknown). Our results suggest that acoustic characteristics of Northern Spotted Owl calls captured with ARUs can be used to identify whether sites have males and/or females present, and we suggest that further investigation into the full repertoire of Northern Spotted Owl call types is warranted.

A recent specimen of a Tasmanian Boobook Ninox leucopsis recovered on Lord Howe Island

On 11 July 2019, during the Rodent Eradication Program on Lord Howe Island using aerial and ground rodentbaiting, the recovery of dead non-target birds included a recently dead boobook Ninox sp. found on a resident’s property. Two Tyto species were also recovered. Despite automated sound-recording equipment stationed within the forests of the Island, no records of Ninox vocalisations were made before discovery of the boobook specimen; however, two instances of Ninox owl calls were reported anecdotally within The Settlement. There was speculation from some Island residents that the recovered boobook could have been an individual of the extinct endemic subspecies, the Lord Howe Boobook N. novaeseelandiae albaria. The boobook was forwarded to the Australian Museum for further visual scrutiny, collection of morphometric data, DNA analysis, and preparation for the Australian Museum collection. There was overlap in plumage and morphological measurements between both the Tasmanian Boobook (N. leucopsis) and the nominate Tasman Morepork from New Zealand (N. n. novaeseelandiae), but the specimen was distinct from the larger Australian mainland N. boobook. DNA analysis provided conclusive evidence that the bird was a male N. leucopsis, exhibiting an overall clean-white spotted pattern and darker brown coloration. The occurrence of a Ninox species on Lord Howe Island is the first record in more than 50 years and should prompt further exploration of the dispersal and possible migration of boobooks from Tasmania.

Behavioral Responses of Wild Rodents to Owl Calls in an Austral Temperate Forest.

Simple SummaryGrowing human populations are challenging scientists to find effective ways to control and mitigate human–wildlife conflict while preserving biodiversity. It has been reported that predator odor and calls can drive away rodents, but little is known about species-specific responses of prey. For these reasons, we compared the behavioral changes of common rodent species inhabiting the Chilean temperate forest (Abrothrix spp., the long-tailed pygmy rice rat Oligoryzomys longicaudatus and the black rat Rattus rattus) when exposed to two different native predator calls (the austral pygmy owl Glaucidium nana and the rufous-legged owl Strix rufipes) and a control (no predator calls). Our results showed that all rodent species modified their behavior in the presence of predator calls, but the effects were species dependent. These findings point to the need to carefully study target rodent species instead of applying a general control plan for all rodent species.Ecologically based rodent management strategies are arising as a sustainable approach to rodent control, allowing us to preserve biodiversity while safeguarding human economic activities. Despite predator signals being known to generally repel rodents, few field-based studies have compared the behavioral effects of several predators on different prey species, especially in Neotropical ecosystems. Here, we used camera traps to study the behavior of rodent species native to the Chilean temperate forest (Abrothrix spp., long-tailed pygmy rice rat Oligoryzomys longicaudatus) and an introduced rodent (black rat Rattus rattus). Using playbacks of raptor calls, we experimentally exposed rodents to three predation risk treatments: austral pygmy owl calls (Glaucidium nana), rufous-legged owl calls (Strix rufipes) and a control treatment (absence of owl calls). We evaluated the effects of the treatments on the time allocated to three behaviors: feeding time, locomotor activity and vigilance. Moonlight and vegetation cover were also considered in the analyses, as they can modify perceived predation risk. Results showed that predator calls and environmental factors modified prey behavior depending not only on the predator species, but also on the rodent species. Consequently, owl playbacks could be regarded as a promising rodent control tool, knowing that future studies would be critical to deeply understand differences between species in order to select the most effective predator cues.

Behavioral responses of rural and urban greater white-toothed shrews (Crocidura russula) to sound disturbance

The development of urban areas imposes challenges that wildlife must adapt to in order to persist in these new habitats. One of the greatest changes brought by urbanization has been an increase in anthropogenic noise, with negative consequences for the natural behavior of animals. Small mammals are particularly vulnerable to urbanization and noise, despite some species having successfully occupied urban environments. To understand some of the traits that have enabled small mammals to deal with the consequences of urbanization, we compared the behavioral responses of urban and rural greater white-toothed shrews, Crocidura russula, to different sound stimuli. A total of 32 shrews, 16 from each habitat, were exposed in captivity to four sound treatments: silence, tawny owl calls, traffic noise, and white noise. Urban and rural shrews showed different behaviors, with urban animals being more active, feeding more frequently, and using less torpor than rural individuals. However, responses to sound treatments were similar in both populations: urban and rural shrews exhibited a slight decrease in activity and feeding behavior, as well as more fleeing responses, when exposed to traffic noise or white noise, but not to owl calls. These results suggest urbanization induces long-term changes in the general activity of C. russula, but the short-term behavioral response to sound disturbance remains similar in rural and urban populations.

Field evaluation for playback surveys: species-specific detection probabilities and distance estimation errors in a nocturnal bird community

ABSTRACT Capsule During playback experiments, the distance from the surveyor to the call influences the chances of detection across nocturnal species in farmland and woodland habitats. Aim To evaluate how distance affects surveyor detection capability, expressed as the probability of hearing broadcast calls and of estimating their distances correctly, in a nocturnal bird community. Methods We conducted a playback field experiment in farmland and woodland areas within an agricultural landscape in winter and summer 2020. Vocalizations of five species (Little Owl Athene noctua, Tawny Owl Strix aluco, Long-eared Owl Asio otus, Common Nightingale Luscinia megarhynchos, Water Rail Rallus aquaticus) were broadcast at various distances to a surveyor, who attempted to detect them and, if successful, to classify them into predefined distance zones. Binomial GLMMs were used to estimate detection probability as a function of distance, and the effects of habitat and season on this relationship. Results The distance of the broadcast call from the surveyor had a significant effect on detection probability in both habitats. In woodland, the probability of hearing calls was significantly higher in winter, while estimating distances correctly was generally higher in summer. An increase in field experience improved our detection capability, mainly in terms of distance estimation, for which errors were mostly overestimates. Conclusions The probability of hearing calls and distance estimation accuracy varied between species. Most Little and Tawny Owl calls were detected within a 200 m radius of the surveyor, while this was 100 m for the other species. For a multi-species community-level study, playback surveys are thus likely to be most representative of a 200 m radius surrounding the surveyor where the probability of detection is highest, while estimates of distance from the observer are likely to be inaccurate in most cases. Field evaluations such as this should be implemented prior to actual playback surveys.

Acoustic localisation of wildlife with low-cost equipment: lower sensitivity, but no loss of precision

Abstract Context Synchronised acoustic recorders can be used as a non-invasive tool to detect and localise sounds of interest, including vocal wildlife and anthropogenic sounds. Due to the high cost of commercial synchronised recorders, acoustic localisation has typically been restricted to small or well funded surveys. Recently, low-cost acoustic recorders have been developed, but until now their efficacy has not been compared with higher specification recorders. Aims The present study aimed to compare the efficacy of a newly developed low-cost recorder, the Conservation at Range through Audio Classification and Localisation (CARACAL), with an established, high-end recorder, the Wildlife Acoustics Song Meter (SM). Methods Four recorders of each type were deployed in a paired set-up across five nights in Wisconsin, USA. The recordings allowed for manual identification of domestic dog (Canis familiaris), grey wolf (Canis lupus), coyote (Canis latrans) and barred owl (Strix varia) calls, and then the ability of each recorder type to detect and localise the vocalising animals was compared. Key results The CARACALs were less sensitive, detecting only 47.5% of wolf, 55% of coyote, 65% of barred owl and 82.5% of dog vocalisations detected by the paired SMs. However, when the same vocalisations were detected on both recorders, localisation was comparable, with no significant difference in the precision or maximum detection ranges. Conclusions Low-cost recording equipment can be used effectively for acoustic localisation of both wild and domestic animals. However, the lower sensitivity of the CARACALs means that a denser network of these recorders would be needed to achieve the same efficacy as the SMs. Deploying a greater number of cheaper recorders increases the labour time in the field and the quantity of data to process and store. Thus, there is a trade-off between cost and time to be considered. Implications The ability to use low-cost recorders for acoustic localisation provides new avenues for tracking, managing and researching a wide range of wildlife species. Presently, CARACALs are more suited to monitoring species that have small home ranges and high amplitude vocalisations, and for when a large time investment for in situ equipment checks and data processing is feasible.

Behavioral Reactions of Naturalized Ring-Tailed Lemurs (Lemur catta) to Native Owl Vocalizations

During routine surveys of owl distributions on St. Catherines Island, we observed naturalized ring-tailed lemurs displaying antipredator responses to owl auditory cues. In the 32 y since the introduction of ring-tailed lemurs to the island, two successful depredation events by two different owl species have been documented. We investigated the behavioral response of ring-tailed lemurs to determine if they responded consistently to social calls from all three owl species present on St. Catherines Island despite size differences among the owl species that could affect the likelihood of them serving as predators on ring-tailed lemurs. We observed while ring-tailed lemurs responded to all the auditory owl calls, they exhibited more intense, longer and more consistent responses to the two larger owl species – the barred owl and great horned owl – relative to the small Eastern screech owl. These data suggest naturalized species are capable of learning threat-sensitive antipredator behaviors to novel predator communities.

Behavioral Reactions of Naturalized Ring-Tailed Lemurs (Lemur catta) to Native Owl Vocalizations

During routine surveys of owl distributions on St. Catherines Island, we observed naturalized ring-tailed lemurs displaying antipredator responses to owl auditory cues. In the 32 y since the introduction of ring-tailed lemurs to the island, two successful depredation events by two different owl species have been documented. We investigated the behavioral response of ring-tailed lemurs to determine if they responded consistently to social calls from all three owl species present on St. Catherines Island despite size differences among the owl species that could affect the likelihood of them serving as predators on ring-tailed lemurs. We observed while ring-tailed lemurs responded to all the auditory owl calls, they exhibited more intense, longer and more consistent responses to the two larger owl species – the barred owl and great horned owl – relative to the small Eastern screech owl. These data suggest naturalized species are capable of learning threat-sensitive antipredator behaviors to novel predator communities.

Can you hear me now? The effect of signal degradation on perceived predator threat in black-capped chickadees (Poecile atricapillus).

Avian predators vary in their degree-of-threat to chickadees; for example, smaller owls and hawks are of higher threat to chickadees as they can easily maneuver through the trees, while larger predators cannot. We conducted an operant go/no-go discrimination task to investigate the effect of signal degradation on perceived threat. Chickadees were trained to respond to high-threat northern saw-whet owl (NSWO) or low-threat great horned owl (GHOW) calls that were recorded at short distances, and then tested with high- and low-threat owl calls that were rebroadcast and re-recorded across six distances (25m, 50m, 75m, 100m, 150m, and 200m). Subjects were further tested with high-threat and low-threat synthetic tones produced to mimic the natural calls across the six distances. We predicted that birds would perceive and respond to: (1) high-threat predator calls at longer distances compared to low-threat predator calls, and (2) synthetic tones similarly compared to the stimuli that they were designed to mimic. We believed chickadees would continue to perceive and respond to predators that pose a high threat at further distances; however, only responding to low-threat stimuli was consistent across distance recordings. Synthetic tones were treated similarly to natural stimuli but at lower response levels. Thus, the results of this study provide insights into how chickadees perceive threat.

Effects of predation risk on the body mass regulation of growing wood mice

AbstractBody mass in wild animals has been suggested to be regulated by the opposing fitness consequences of variation in body size (and fat storage) for starvation and predation risk. Many studies of adult mammals and birds have broadly confirmed the predictions of this model. However, relatively few studies have addressed the potential role of such trade‐offs during early phases of development when animals are growing. Similarly, studies of the impact of high‐fat diets on wild small mammals generally show a resistance to weight gain. But whether growing animals are similarly resistant is unclear. In this study, weaned wood mice (Apodemus sylvaticus) were exposed to a high risk of predation, simulated by the broadcasting of owl calls, for 66 days during which body mass and energy intake were monitored. We hypothesized that if the risk of predation plays a role in regulating body mass during this phase then animals growing under predation risk would grow less. We found female (but not male) mice exposed to the predation risk treatment had lower growth rates and ended the experiment lighter; however, variations in energy intake and resting metabolic rate did not explain the observed differences. Feeding on high‐fat diet resulted in individuals with higher body mass. Females reached their adult size earlier than males and were more responsive to the predation risk treatment when feeding on high‐fat diet. Our data suggest males body mass to have fitness consequences on social dominance and reproductive success not accounted for in the simple starvation‐predation trade‐off model.

Environmental conditions and call-broadcast influence detection of eastern forest owls during standardized surveys

AbstractOwls play crucial roles in the environment and provide ecosystem services making them important to monitor and study. However, standardized methods for most species do not exist, and we lack understanding of the effects of many environmental variables and call-broadcast on detection of owls during surveys. We performed a multispecies occupancy analysis of owl monitoring data collected from 2004 to 2013 across the state of Maine to examine the effects of environmental variables, conspecific and heterospecific call-broadcast, and general survey protocols on detection of 3 forest owls: Northern Saw-whet Owl (Aegolius acadicus), Barred Owl (Strix varia), and Great Horned Owl (Bubo virginianus). We found that environmental variables such as cloud cover, precipitation, temperature, time of night, and wind had species-specific effects on detection probability, and ambient noise decreased detection probability for all species. Snow cover did not affect detection of any species. We also found that conspecific call-broadcast increased detection of each species, while heterospecific call-broadcast had variable effects. Specifically, we found that Long-eared and Barred owl broadcast increased the detection of Northern Saw-whet Owl, and our results suggest additional heterospecific effects may exist. Our study showed that, compared to the protocol of the Maine Owl Monitoring Program, surveys simultaneously examining all 3 of our focal species can increase efficiency and lower disturbance by only broadcasting Long-eared and Barred owl calls during a 10-min survey. We recommend that future owl surveys take into account species-specific effects of conspecific and heterospecific call-broadcast, and use our results when designing survey protocols that include one or more of our focal species.

Traffic noise and responses to a simulated approaching avian predator in mixed‐species flocks of chickadees, titmice, and nuthatches

AbstractTraffic noise likely reaches a wide range of species and populations throughout the world, but we still know relatively little about how it affects anti‐predator behavior of populations. We tested for possible effects of traffic noise on responses to predator acoustic cues in Carolina chickadees (Poecile carolinensis), tufted titmice (Baeolophus bicolor), and white‐breasted nuthatches (Sitta carolinensis) near 14 independent feeding stations in eastern Tennessee. We compared anti‐predator calling and seed‐taking behavior in response to playbacks of predator stimuli (screech owl calls) at sites naturally exposed to traffic noise and at sites that faced relatively little traffic noise. The screech owl call playback was designed to simulate the approach of this dangerous predator to a feeder being used by these small songbirds. We found that chickadees responded consistently to the owl stimuli across different levels of traffic noise. However, titmice, and nuthatches exhibited different behavioral responses to the predator stimulus, suggesting that traffic noise masked these low‐frequency predator calls. Overall, chickadees and nuthatches showed the broadest anti‐predator behavioral responses in comparison to titmice, corroborating earlier published work with an Indiana population. Finally, populations exposed to traffic noise overall seemed less able to detect predator cues potentially masked by that noise, and future work will need to assess likely seasonal variation in these responses as well as species‐level variation in anti‐predator responses in mixed‐species groups.

Automated identification of avian vocalizations with deep convolutional neural networks

AbstractPassive acoustic monitoring is an emerging approach to wildlife monitoring that leverages recent improvements in automated recording units and other technologies. A central challenge of this approach is the task of locating and identifying target species vocalizations in large volumes of audio data. To address this issue, we developed an efficient data processing pipeline using a deep convolutional neural network (CNN) to automate the detection of owl vocalizations in spectrograms generated from unprocessed field recordings. While the project was initially focused on spotted and barred owls, we also trained the network to recognize northern saw‐whet owl, great horned owl, northern pygmy‐owl, and western screech‐owl. Although classification performance varies across species, initial results are promising. Recall, or the proportion of calls in the dataset that are detected and correctly identified, ranged from 63.1% for barred owl to 91.5% for spotted owl based on raw network output. Precision, the rate of true positives among apparent detections, ranged from 0.4% for spotted owl to 77.1% for northern saw‐whet owl based on raw output. In limited tests, the CNN performed as well as or better than human technicians at detecting owl calls. Our model output is suitable for developing species encounter histories for occupancy models and other analyses. We believe our approach is sufficiently general to support long‐term, large‐scale monitoring of a broad range of species beyond our target species list, including birds, mammals, and others.

Effects of Broadcasting Calls on Detection Probability in Occupancy Analyses of Multiple Raptor Species

For population studies that rely on aural or visual observations of individuals, methods that induce a detectable response can greatly improve sample sizes and reduce costs. Numerous authors have reported improved detections using broadcast surveys in forested areas for various species of raptors; however, to our knowledge, none have attempted to quantify the effects of broadcast surveys on the detection probability (p) in the context of an occupancy study for multiple species. Our objective was to determine whether broadcasting conspecific and heterospecific calls (broadcast surveys) would increase p of raptor species compared to passive surveys. This comparison was accomplished by estimating p during both types of surveys using a multiscale occupancy framework. We conducted 8400 surveys for Cooper's Hawk (Accipiter cooperii), Swainson's Hawk (Buteo swainsoni), White-tailed Hawk (Geranoaetus albicaudatus), Harris's Hawk (Parabuteo unicinctus), Red-tailed Hawk (Buteo jamaicensis), and Great Horned Owl (Bubo virginianus) in 2015 and 2016 in south Texas. We conducted 10-min passive surveys in both years, 10-min broadcast surveys in 2015 including calls from each of the target hawk species, and 10-min broadcast surveys in 2016 using calls from Great Horned Owls. Our results suggest that p is improved with multiple-hawk broadcast surveys (0.16, SE 0.04) over passive surveys (0.04, SE 0.02) for Harris's Hawks; p was not affected in broadcast surveys for the other hawk species considered. Great Horned Owls had a higher p during broadcast surveys using Great Horned Owl calls (0.35, SE 0.04) than during passive surveys (0.19, SE 0.02). Our results do not support the use of broadcast surveys to improve the detection probability of multiple species of hawks. However, our results do indicate that using broadcast surveys for occupancy studies focused on Harris's Hawks or Great Horned Owls should significantly reduce the effort required over passive surveys, resulting in improved power and reduced costs.

Heed the call to change.

I needed a change. Just a few years earlier, I stood at the edge of the swamp under a massive hollow cypress tree reading Winnie-the-Pooh to a group of 5- and 6-year-olds. As a naturalist at a state park, my goal was to introduce these children to the nature found in their own backyard. I played a tape of owl calls to accompany the story. Just then, an owl swooped down over our heads, startling and delighting us. “I can't believe I'm actually getting paid to have this much fun!” I thought to myself. But over time, my job changed. Sitting at my desk, staring at environmental impact reports and grant applications on my computer screen, I began to think, “They cannot pay me enough to do this job.” It was another turning point in the winding road that led me, at age 66, to earn a Ph.D. ![Figure][1] ILLUSTRATION: ROBERT NEUBECKER > “I was 60 years old. … But I wanted to follow my new passion.” My first career had been audiology—a pragmatic choice based on job opportunities in a rural area, and one that allowed me to work part time while tending my growing family. But when my children grew up and left home, I found myself longing to be outside, not in a soundproof room in the hospital basement. I began attending ornithology classes at the local university, hoping that might lead me to new career prospects. I also went to see a career counselor, offered as part of a university program for nontraditional students. “What gave you pleasure as a child?” the counselor asked. I thought for a while before responding, “Playing outside in the woods.” Our discussion eventually led to a second master's degree, this one in zoology, and the job as a naturalist at a state park. It was an entry-level position. I was 44 years old. And I was delighted to once again experience the joy of being outdoors that I had felt as a child. But as I climbed the career ladder at my state's Department of Natural Resources, from naturalist to grant compliance officer to managing environmental reviews of publicly funded conservation projects, my time in the field diminished and finally disappeared. I was chained to a computer screen. In the back of my mind, the career counselor's question smoldered. “What gave you pleasure as a child?” As my discontent grew, life went on. At a dinner party, my friends and I discussed the perfect retirement. We agreed that, if money were not an issue, we would each purchase a home in a different part of the world and rotate among them. Shortly thereafter, an opportunity presented itself: a 4-month sabbatical at a university in the Netherlands as part of a field research project. It wasn't quite the house-share plan, but it had the appeal of being someplace new. I found that field research allowed me to play in the woods again, but with a new purpose. I was able to combine my childhood delight in nature with the intellectual stimulation that comes with figuring things out—pleasures that had become all too rare in my job. At the end of my stay, I was invited to participate in the “sandwich” Ph.D. program, in which students do research in their home country while receiving support and instruction in the Netherlands. I was 60 years old. I didn't think that earning a Ph.D. would further my career. But I wanted to follow my new passion. I figured that I could work full time at my day job in the state government and conduct my research during evenings and weekends. Still, my colleagues raised their eyebrows. “What do you intend to do with a Ph.D.?” they asked. “It is all about the journey,” I responded. I successfully defended my dissertation 6 years later, 3 years after retiring from my government position. My career path has taken some sharp zigs and zags over my 40 years in the workforce. And each decision I made was the right one for me at the time. But when they were no longer right, I changed direction. No career decision has to be final. As one of my favorite authors, Ursula K. Le Guin, wrote, “It is good to have an end to journey towards, but it is the journey that matters in the end.” [1]: pending:yes

Simulated Owl Predation Risk to Voles Modifies Browsing Effects on Tree Seedling Growth

Browsing effects of voles on plants can be mitigated by means of non-lethal predation, i.e. by subjecting voles to predator cues. Earlier studies largely focused on mammalian olfactory cues, whereas here we exposed Microtus voles to owl calls to examine whether the introduced predation risk reduces browsing on tree seedlings (silver birch, Scots pine, Norway spruce). We found that owl risk was associated with higher growth rate of birch seedlings, but only late in the growing season, while there was no obvious effect in case of pine and spruce. Early in the season, in the absence of predation risk, voles were able to move freely and search for their preferred food, grasses. Late in the season, when grasses were less palatable, voles likely targeted birch seedlings to a higher degree. Our results suggest that owl calls could alleviate vole herbivory on birches but, at least on a short temporal scale, will not protect seedlings of conifers.

Vocal Individuality of Sunda Scops-Owl (Otus lempiji) in Peninsular Malaysia

Like many owl species, Sunda Scops-Owls (Otus lempiji) are difficult to monitor using traditional survey techniques, because of their nocturnal habits, secretive nature, and cryptic coloration. Individual variation in vocalizations could potentially be used to distinguish individuals of this owl species, as has been demonstrated for many bird species. The objectives of this study were to describe the territorial call of Sunda Scops-Owls, to determine whether the calls can be distinguished individually, and to examine whether the calls from the same individuals were stable over time. We analyzed 75 recordings collected from 12 owls from December 2014 to June 2015 in a lowland forest and oil palm smallholdings in Selangor State, Peninsular Malaysia. Using two temporal parameters and six frequency parameters derived from spectrogram, we employed ANOVA tests and found significant differences for all parameters among individual owls. Discriminant function analysis correctly classified 97.1% of the owl calls to the correct individuals. Based on the Wilcoxon signed-rank test, all vocal parameters did not vary significantly for the six birds that were vocally active over two predetermined survey sessions within the breeding period. Our results demonstrated that Sunda Scops-Owls can be identified individually by their vocalizations. This implies that assessing vocal individuality can be useful as a noninvasive method for surveying the Sunda Scops-Owls and the method should be further tested for other little-known owl species in the tropics.