Many researchers have suggested that abundance of Burrowing Owls (Athene cunicularia) has declined in many portions of their breeding range, but a thorough review of their population trends over time is lacking. Published population trends from the North American Breeding Bird Survey program suggested that Burrowing Owl populations in the US have declined over the past 60 yr, but the declines were not considered significant until 2014. However, accurate trend estimates and the statistical significance of those estimates were hampered by low relative abundance of owls. Moreover, many authors have suggested that eradication of burrowing animals is a major cause of Burrowing Owl declines, because burrows dug by burrowing animals are a critical resource for Western Burrowing Owls (A. cunicularia hypugaea). Despite this, we currently lack a range-wide summary of the burrowing animals on which Western Burrowing Owls depend. To help fill these two information gaps, my objectives were to: (1) use Breeding Bird Survey (BBS) data to examine geographic patterns in population trends of Burrowing Owls throughout their breeding range in the USA, and (2) use past studies to provide the first summary of the spatial extent to which Western Burrowing Owls rely on the suite of burrowing animals throughout their breeding range. Significantly more BBS routes in the US show declining counts of owls than show increasing or stable counts, and the declines were most apparent prior to 1995. Counts of Burrowing Owls declined most precipitously on the northern edge and southern edge of the owl's US breeding range. Western Burrowing Owls primarily use black-tailed prairie dog (Cynomys ludovicianus) burrows in the eastern portion of their breeding range, whereas the diversity of burrowing species on which the owls depend is much greater in the western and central portions of their breeding range. Burrowing owl declines have been most apparent in portions of their range where they rely primarily on Richardson's ground squirrels (Urocitellus richardsonii), California ground squirrels (Otospermophilus beecheyi), black-tailed prairie dogs, and American badgers (Taxidea taxus).

Breeding dispersal, the movement between successive breeding sites, is important to many aspects of life history and population dynamics but poorly understood for many raptor populations. We used longitudinal data collected from Burrowing Owls (Athene cunicularia) nesting in southwestern Idaho from 1994–2007 to examine characteristics of breeding dispersal behavior. First, we measured frequency and distance of breeding dispersal and compared those to published results from other owl populations. The dispersal frequency (78%, n = 86) was greater than previously reported for any Burrowing Owl population and for most owl species. The mean distance dispersed (835 ± 98 m [SE]) was slightly greater than reported distances for most other Burrowing Owl populations. Second, we examined factors associated with two decisions owls faced between breeding seasons: whether to move to a new nest site (dispersal likelihood), and how far to move if dispersing to a new site (dispersal distance). We assessed the potential effects of sex, productivity, age, and site quality on breeding dispersal likelihood and distance. Owls were more likely to disperse if they were female and if they had fledged fewer young in the previous breeding season. Nesting failure was a perfect predictor of breeding dispersal, but high productivity did not always result in philopatry. Owls dispersed farther if they were relatively younger, female, had lower productivity in the previous breeding season, and had previously nested in lower quality sites. Our comparisons to other studies indicate that the factors that most influence breeding dispersal behavior in Burrowing Owls appear to vary among populations and may relate to migration tendency and geographic heterogeneity.

In some areas, Burrowing Owls (Athene cunicularia) occur in human-altered, urbanized environments. However, their use of these anthropogenic land-cover types during nighttime is not well understood. We studied nocturnal and crepuscular space-use of eight juvenile Burrowing Owls in urban, greenspace, and agriculture dominated landscapes during 2012 and 2013 in Doña Ana County, New Mexico. For each owl, we obtained an average of 22 (range 14–37) nighttime telemetry fixes covering a period of 1–8.5 wk post-fledging. The juvenile Burrowing Owls avoided urban cover types and spent more time in agriculture and greenspace. In agricultural areas, owls used canals, weedy ditches, and associated farm roads, whereas in greenspace owls used city parks, golf courses, and patches of native habitat. Juvenile owls in this study were not observed to move large distances and on average most owls (n = 5) remained within 500 m of their roost burrow, with one owl traveling up to 743 m from its roost site. Conservation efforts for Burrowing Owls within human-altered environments should focus on the protection of nest and roost burrows near important foraging areas.

One common strategy to mitigate the loss of natural nest burrows for Burrowing Owls (Athene cunicularia) from ground-disturbing activities has been the installation of artificial burrows outside the disturbance area. I assessed the effectiveness of artificial burrows as a mitigation tool at two study sites in northern California. Parameters included nesting success at natural and artificial burrows; long-term occupancy rates of maintained and unmaintained artificial burrows; choice of burrow type (natural vs. artificial burrows) by owls raised in artificial burrows; and site fidelity and natal philopatry of Burrowing Owls raised in artificial burrows. I analyzed long-term datasets biologists collected from 1990 through 2012, including demographic data, band resightings, and burrow maintenance records. Nesting success at artificial burrows was significantly higher than at natural burrows at both study sites. At one site, nesting success at artificial burrows was 83% compared to 76% at natural burrows (P = 0.035); at the other site, nesting success at artificial burrows was 96% compared to 75% at natural burrows (P = 0.036). Artificial burrows that received annual surface maintenance were occupied for a significantly longer time (2.1 ± 1.9 yr; n = 57) than unmaintained artificial burrows (0.5 ±1.0 yr, n = 51; U = 561, P < 0.001) during the first 8 yr post-installation. Even with surface maintenance, occupancy rates declined from 44% (n = 25) of burrows occupied during the first year post-installation, to 28% (n = 15) of burrows occupied during the fourth year post-installation. Based on this decline, regular maintenance of the entire artificial burrow, including tunnel and nest chamber, may be crucial for longer-term use. Of 120 Burrowing Owls raised in maintained artificial burrows and resighted during subsequent breeding seasons, 70% occupied artificial burrows and 30% natural burrows. Only 3% of these owls occupied their natal burrow during the first nesting season post-fledging. Of those owls that were resighted during two or more nesting seasons, almost half (48%) occupied different artificial burrows from one year to the next; therefore, the number of artificial burrows at a management site should be sufficient to provide opportunities for Burrowing Owls to move between nest burrows from year to year.

The winter home ranges, foraging habitats, and roost characteristics of migrant Burrowing Owls (Athene cunicularia) have not been described in central Mexico. This information is needed to prioritize habitat conservation measures because the species is in decline across much of western North America. We used VHF telemetry to describe the foraging range, habitat use, and roost sites of 17 Burrowing Owls in two study areas: Irapuato and Zapopan, Mexico. Burrowing Owls did not forage in the daytime. Cropland and grasslands made up the majority of the owls' foraging ranges, which averaged 70 ha. Burrowing Owls responded quickly and opportunistically to changes in land uses that removed tall dense vegetation, such as the harvest of tall crops, and fires. Distances from foraging areas to roost sites averaged 514–751 m, but varied widely from 32–1981 m. Roost characteristics were highly variable between study sites. Overall, Burrowing Owls incorporated anthropogenic land uses into their winter habitat needs.

Western Burrowing Owls (Athene cunicularia hypugaea) frequently nest near agricultural lands. In southwestern Idaho, greater population density in agricultural landscapes appears to be driven in part by reliable and abundant prey populations. However, these potential benefits may be offset if agricultural land use increases pesticide exposure, especially during the sensitive reproduction period. Thus, we investigated the extent to which Burrowing Owls nesting near croplands within the Morley Nelson Snake River Birds of Prey National Conservation Area (NCA), Idaho, were exposed to organophosphate (OP), carbamate (CB), and/or organochlorine (OC) pesticides. We examined plasma cholinesterase activity, OP and CB residues in foot-wash samples, and OCs in soils and whole egg contents collected from owls and their nests along a distance gradient from agricultural fields. We further measured eggshell thickness to assess potential for thinning from OC exposure. There was no inhibition of cholinesterase activities in adult or nestling owls near agriculture, and foot-wash samples from adults tested negative for OP and CB pesticides. The OC p,p′-DDE, a metabolite of DDT, occurred in eggs at 27 of 58 nests, but there was some evidence that concentrations increased with increasing distance from agriculture. Concentrations of p,p′-DDE in eggs were relatively low compared to harmful levels in other avian species, were not correlated with eggshell thickness, and did not appear to reduce nesting success. Neither DDT, its metabolites, nor any other OCs were detected in soil samples from local owl breeding areas. These results indicate that p,p′-DDE, organophosphate, and carbamate exposure were not causing toxicity or reproductive impairment of Burrowing Owls in the NCA during our study years.

The purpose of this review is to present a brief overview of literature published through 2016 on the Burrowing Owl (BUOW; Athene cunicularia) as an example of how the science of bibliometrics allows us to examine the literature on this species and to determine and display important trends, including gaps in that literature. We conducted various analyses on approximately 1681 BUOW articles to demonstrate the utility of bibliometrics. We also compare the effectiveness of a traditional bibliography versus online databases. The query of even several online databases does not guarantee identifying but a fraction of the total references. Even the most complete database searched for the term “Athene cunicularia” produced only 38% of those of the current World Owl Bibliography Update. Topical areas that seem absent or limited in the published literature include: the genetics of many subspecies of this owl; the population status and trend in intact ecosystems versus human-altered habitats; details on the demography of Burrowing Owls in Central and South America; migratory patterns and overwintering habitat conditions; the dispersal and movement of several metapopulations; successful mitigation strategies; the effectiveness of translocation; the effect of various artificial burrow designs on interior microclimate and owl reproductive success; and a more comprehensive approach to management. This is an ongoing project that will contribute to a larger update of the literature on the owls of the world.

Secondary exposure to anticoagulant rodenticides (ARs) through consumption of contaminated prey has been documented worldwide in many non-target species, especially raptors. The Red-tailed Hawk (Buteo jamaicensis), a raptor that frequents agricultural areas and eats primarily rodents, is particularly susceptible. Because there is documentation of Red-tailed Hawk exposure to ARs in California, this study aims to describe the extent to which migrating juvenile Red-tailed Hawks are exposed to ARs, as well as any sublethal effects of AR ingestion. We collected blood samples and body morphometrics from 97 juvenile Red-tailed Hawks migrating through the Marin Headlands, Marin County, CA, from August to December in 2013 and 2015, and screened samples for the presence of ARs. Eight hawks (8.2%) tested positive for some amount of ARs. We detected first-generation (diphacinone, chlorophacinone) and second-generation (brodifacoum, bromadiolone) ARs. Although some juvenile Red-tailed Hawks are exposed to ARs either along their migration route or as resident birds in the Marin Headlands, we did not find any relationship between body condition and presence of ARs. Although this method of AR sampling of live birds is novel and increases our sampling capabilities, the short half-lives of ARs in blood make it difficult to estimate population-wide exposure rates. Future studies should focus on resident raptors near agricultural areas where AR exposure can be tested over time to better understand how this technique can be used to estimate exposure rates across whole populations.

Satellite telemetry is widely used to generate information on species' use of space, which contributes to meeting conservation goals. Between June 2015 and September 2016, we obtained approximately 11,000 GPS points from two adult male Andean Condors (Vultur gryphus) that had been fitted with satellite transmitters and released in the central Andes of Peru. We used GPS coordinates and associated data to produce habitat distribution models (binomial Generalized Linear Models) from presence and pseudo-absence data of roosting sites and foraging areas visited by these individuals. The best potential habitats for Andean Condors in Peru were west of the Andes, from the border with Ecuador, south to Bolivia and Chile. Foraging areas of both individuals were at higher elevations than roosting sites (means: 3934 masl and 3356 masl, respectively). Roosting sites were in areas dominated by grasslands and agriculture, whereas foraging areas were dominated by puna grassland and brush. Conservation strategies for Andean Condors in Peru should be informed by data derived from satellite telemetry and should focus on preserving natural short vegetation above 3000 m west of the Andes for foraging and, for roosting sites, on maintaining areas free from the disturbances of road construction.

The Mottled Wood-Owl (Strix ocellata) is a poorly studied species endemic to the Indian subcontinent. During nine nesting seasons from 2005–2016, we studied 15 breeding pairs near Pune, west-central India. Important nest tree species were mango (Mangifera indica, 52%) and tamarind (Tamarindus indica, 22%). Habitat in plots with a 0.5-km radius centered on the nest comprised a mosaic of agricultural landscapes (41.9 ± 17.7%), deciduous/scrub forests (16.8 ± 21.8%), natural grasslands (15.0 ± 8.2%), human habitation (11.2 ± 8.5%), streams/rivers (10.1 ± 4.6%), and low hills (5.0 ± 5.8%). In a subset of five nests where the entire breeding cycle was studied, the average clutch size was 2.6 eggs (±0.5 SD, n = 20 breeding attempts [eggs laid]), of which an average 2.2 (± 0.4) young hatched, and 1.9 (±0.8) young fledged/ breeding attempt. In addition, among ten other pairs where the nests were detected at the stage of fledging of young, an average of 1.6 young (±0.7, range = 1–4) fledged / successful nest. The primary nesting season from egg-laying to fledging lasted from 10 February until 20 May. From 1033 pellets analyzed, we identified 711 prey, including insects (39%), small mammals (rodents 10%; shrews 21%, bats 3%), birds (11%), and reptiles (9%).

Northern Saw-whet Owls (Aegolius acadicus) are banded across the United States, yet neither migration nor dispersal of Northern Saw-whet Owls are fully understood. In spring of 2007 and 2008, the banding station at Whitefish Point Bird Observatory in Michigan's Upper Peninsula began broadcasting male and female (respectively) audio lures at dedicated net arrays to complement the passive mist netting performed since 1994. We analyzed data from spring owl captures (1994–2016) that used either male “advertising call” audio lures, female “tssst” audio lures, or no audio lures. From the analysis of 6659 owls captured during that period, we found that (1) there was a substantial female-bias in the owls caught at the passive and male audio lure nets, (2) a more extreme female-bias in the owls caught at the male audio-lure nets than the passive nets, and (3) a nearly equal proportion of male and female owls caught at the female audio-lure nets. These results corroborate a model of differential migration, in which females compose a larger portion of migrating Northern Saw-whet Owls than males. We also found that audio lures that use female calls can increase relative capture rates of male Northern Saw-whet Owls during spring migration.

Most raptor species rely on perches for hunting, resting, preening, and roosting, and in many agricultural areas the availability of adequate perches can limit raptor abundance and diversity. This has negative implications for both raptor conservation and for the provisioning of natural pest control services for farmers. Installing artificial perches on agricultural lands can therefore benefit both raptors and farmers, but perches must be installed in optimal locations to maximize raptor use and minimize unnecessary costs to farmers. We monitored raptor use of artificial perches in a California vineyard over winter using remote photography to compare two sets of perch types: perches at the top versus perches at the bottom of a steep hill, and perches located among trees versus perches located in an open area. We found that raptors preferred perches on hilltops over perches at the base of hills, and that raptors seem to prefer perches in open habitat over perches located adjacent to trees, although a small sample size for this comparison limited our analysis.

To determine whether Eastern Screech-Owls (Megascops asio; hereafter “screech-owl”) typically guard or avoid food items cached within cavities, we conducted an experiment involving the addition of dead mice to paired roosting boxes during the nonbreeding season. Multiple factors may influence the tendency of a screech-owl to cache food: the value of the item(s), the likelihood of pilferage, the degree to which cached carcasses attract predators, and the availability of alternative cavities for roosting and/or caching. We hypothesized that providing roosting screech-owls with paired cavities (nest boxes) and a standardized windfall of food could reveal important information about food-caching behavior in this species. Twice per month over the course of a winter, we provided roosting owls with either 200 g of frozen mice or nothing on day 1 of the experiment. On day 2, we visited all box pairs occupied on day 1 and determined whether the experimental and control owls remained in the original box, shifted to the adjacent box, or roosted elsewhere. We also noted whether the experimental owls sought to scatter-hoard the mice by moving some into the adjacent box. We found that screech-owls neither guard nor avoid prey in roosting cavities: owls provided with mice shifted roost sites at the same frequency as owls not provided with mice. Additionally, we found no evidence that screech-owls scatter-hoard prey into an adjacent cavity when provided with a windfall of food.