The Harris's Hawk (Parabuteo unicinctus), a social raptor species, often breeds and hunts cooperatively in groups typically consisting of a dominant breeding pair and one or more auxiliary group members. Why these birds form social groups is not completely understood, but one hypothesis is that the ability to hunt cooperatively may benefit groups with a higher hunting success rate or facilitate the capture of larger prey than an individual hawk could catch on its own. To test the hypothesis that group hunting affects patterns of prey delivery and the types of prey delivered to nests, we recorded videos of prey deliveries in May and June at nests of five breeding groups and five breeding pairs in Cameron County and Willacy County, Texas. In contrast to the diets of Harris's Hawks in New Mexico and Arizona that depend heavily on lagomorphs, we documented mostly avian prey items (39.1% of prey deliveries) and rodent prey items (39.1%), and only 0.7% lagomorphs (n = 284 prey items recorded). Significantly more prey items per day were delivered to nests with more nestlings. Importantly, and contrary to our hypothesis, pairs delivered more prey items per day on average than groups; this pattern was not significant, but this may be attributable in part to a small sample size of nests. These results suggest that the presence of auxiliaries may not necessarily provide direct benefits to offspring during the nest provisioning stage at late spring and summer nests in south Texas.

Changes in autumn raptor migration phenology have been documented at hawk count sites across North America. Delays in autumn migration are the most common shift reported, but these changes vary by species. We examined autumn raptor phenology and changes in count effort for 14 raptor species over 46 yr at Hawk Ridge in Duluth, Minnesota, USA, using mean passage date. Among the 14 raptors, six species showed significant shifts in migration phenology; four toward later migration and two toward earlier migration. Our results suggest fewer species are shifting toward later phenology than previously reported at Hawk Ridge and that some previously reported changes in phenology may be explained by changes in survey effort. This study highlights the importance of controlling for count effort when analyzing migration phenology, emphasizing the need for consistent effort in the future.

Winter irruption refers to an unpredictable increase in the number of individuals usually dominated by one age class, either juvenile or adult, into a given area as a response to fluctuations in the food supply. Irruptions are well documented for avian predators breeding in the Arctic and Subarctic regions whereby individuals irrupt into irregular nonbreeding areas across the Boreal Temperate Region. However, this phenomenon is largely unknown across the Austral Temperate Region. We studied the age class composition of Variable Hawks (Geranoaetus polyosoma) and Black-chested Buzzard-Eagles (G. melanoleucus) during six austral winters (nonbreeding season) at an overlapping breeding and overwintering area in the Monte Desert (semiarid grassland and shrub steppes) of the Andean foothills at Mendoza province in central Argentina (33°S). We measured the overall abundance per winter (combining the five age classes) and calculated the relative abundance per age class for each winter of both species. We used the ratio of total number of individuals observed in a single winter/the total hours of observation per winter as an index of abundance, because sampling effort was not equal across winters. We found that (1) both species exhibited winter irruptions, (2) the irruptions were largely driven by a marked increase of Basic I individuals (the youngest age class); at the same time, Basic V individuals (the oldest age class) exhibited their (modestly) lowest abundance, and (3) winter irruptions might be species-specific, as the responses differed between the two species, with a joint irruption event in the austral winter 2016 and a second irruptive event only recorded for Black-chested Buzzard-Eagles in the austral winter of 2018. We posit that the marked increase of Basic I individuals during the irruptive winters cannot be fully explained by successful breeding of the local population, and is likely largely a result of individuals born elsewhere, presumably at southern latitudes, and overwintering at our study site in central Argentina.

Although there are a variety of methods available for trapping raptors, some species, such as Northern Harriers (Circus hudsonius), are not easily captured with standard methods. We tested several existing trapping methods and modified two of them based on Northern Harrier ecology and behavior across seasons in a study population in California. No previously successful methods described in the literature were effective for our study population. Two modified methods were most effective for trapping Northern Harriers: (1) placing two dho-gazas around the nest in a V-shape and flushing the adult female into the nets during the breeding season, and (2) using remote-triggered bow nets baited with waterbird carcasses in winter. Dho-gazas at the nest worked well during the early nestling-rearing stage, when nestlings were younger than 2 wk old and adult females were most attentive. This method was not suitable during the incubation stage because Northern Harriers are prone to nest abandonment. In the winter, Northern Harriers are known to scavenge, yet this aspect of their behavioral ecology has previously been rarely exploited for trapping purposes. These two methods allow for selective Northern Harrier trapping across seasons and provide modified options for research on this understudied and declining species in North America.

Despite the recent surge in ornithological research in South Asia, raptors remain poorly studied. Inadequate information on the regional status and ecology of birds of prey hinders development of effective conservation measures. Our meta-analysis that focused on trends of scientific research on diurnal raptors in India found 478 published articles on 78 raptor species. We used the online databases of Google Scholar, Scopus, and the Journal of the Bombay Natural History Society to develop regional research and conservation priority indices (RCPI) for raptors, using the tool originally developed by Buechley et al. (Diversity and Distributions 25:856–869, 2019) for the raptors of the world. Published literature on raptors in India was highly skewed; most were either anecdotal reports about common species, or studies focused on vultures, whose local extirpations received significant attention. Twenty-one raptor species, of which two are near threatened and three vulnerable, were specifically studied in fewer than five publications. Even many common species are similarly poorly studied. The regional raptor RCPI was highest for the Andaman Serpent-Eagle (Spilornis elgini; 0.71) and lowest for Black Kites (Milvus migrans; 0.11). Several species that received high priority scores are vulnerable to extirpation due to factors such as habitat loss, poisoning, electrocutions, and other threats. We conclude that assessment of the species-bias in published studies will help researchers identify and address the knowledge gaps. This will ultimately help conservationists and managers devise effective regional and country-specific management strategies. We recommend further regional contextualization of the RCPI.

Ospreys (Pandion haliaetus) are obligate piscivores and their nesting success depends on sufficient amounts of fish delivered to the nests during the breeding season. Nests are considered successful when pairs raise a minimum of one young to fledging or near-fledging age. Through web cameras and online broadcasts of Osprey nests, citizen scientists quantified daily number of fish deliveries, nest survival, and nest success. We received and analyzed curated data (one to seven seasons, 2014–2020) from citizen scientist groups representing 19 Osprey web cameras from four countries in North America and Europe. We compared the average and the coefficient of variation of the number of fish delivered per day within the early breeding season between the failed and successful nests using a Wilcoxon rank-sum test. We also analyzed the effects of the average and the coefficient of variation of the number of fish delivered per day on the number of days of nest survival and whether a nest was successful or not using generalized linear mixed models. Successful and failed nests had significant differences in the average number of fish delivered per day and the failed nests had a higher variation in the number of fish deliveries. Moreover, the variation and average number of fish delivered per day had strong associations with whether a nest would fail or succeed. The global effort and manner in which these data were collected are novel and can further our understanding of this charismatic species. The combination of citizen science and technology is a powerful modern tool that can provide insights and has the potential to advance raptor research worldwide.

Little is known about the breeding ecology of Hook-billed Kites (Chondrohierax uncinatus). This is the first study in Belize on this highly specialized, secretive, and uncommon Neotropical raptor species, which is showing a decreasing population trend according to the International Union for the Conservation of Nature. We monitored six Hook-billed Kite nesting attempts over a 3-yr period (2012–2014), presumably all involving the same pair nesting at a single location in the Cayo District of Belize, Central America. For each nesting attempt, we documented phenology, nest and nest-site characteristics, incubation and nestling periods, productivity, and diet. Of the six nests where eggs were observed, three had two eggs. Fledging production averaged 1.7 ± 0.5 (SD) young per nesting attempt. The male and female equitably shared incubation roles (male = 49%, female = 51%) and hunted to feed themselves during the incubation period, which is uncommon in raptors. The nestling period ranged from 20–27 d between 3 May and 18 October. Fledging coincided with or occurred after the onset of the wet season. Prey delivered to the nests comprised two species of arboreal land snails: Orthalicus princeps (99%) and Euglandina ghiesbreghti (1%). Three of the six nesting attempts occurred consecutively in 2014 and produced a combined total of five fledglings (first and third attempts fledged two young and second attempt fledged one young). This represents the first observation of successful triple brooding among Hook-billed Kites during a single breeding season. Triple brooding rarely occurs among raptors and more typically follows early nesting failure. Understanding the basic breeding biology of Hook-billed Kites is important given their highly specialized ecology, which makes them especially vulnerable to climate change and habitat loss.

Determining the diet of species that nest underground, such as the Burrowing Owl (Athene cunicularia), is challenging. Prey information for Burrowing Owls is often limited to prey remains at nest sites and in owl pellets, images collected from above-ground trail cameras, or direct observations of prey acquisition and delivery. To document prey use and nesting behaviors, we equipped an artificial nest box and burrows at Rio Bosque Wetlands Park in El Paso, Texas, with a digital video recorder and three underground infrared cameras. Herein we document the types and frequencies of prey items delivered inside the nest box during the 2019 nesting season, as reflected in videos and images collected continuously from 1 April to 5 July. We reviewed 23,039 video files and documented 580 prey deliveries. We identified 463 (80%) of the delivered prey items to class and 237 items (41%) to family. Invertebrates made up 75% and vertebrates 25% of the identifiable prey items by frequency. Most (55%) of the invertebrates were insects, especially in the orders Orthoptera and Blattodea; scorpions (Scorpiones) were the second most common group (2% of all items). Vertebrate prey were delivered less often and mostly consisted of rodents (14% of all prey items), especially heteromyids, followed by squamate reptiles (6%). Results from this project will aid in conservation and management of this species.

The sex ratio is an important concept in estimating population demography, and such data could contribute to both theoretical research and conservation. Although numerous studies have analyzed the sex ratios of raptors in the wild, few studies have focused on the sex ratios of raptors in wildlife rehabilitation facilities. Here, we report the results of polymerase chain reaction (PCR)-based sex identification of raptors brought to the Beijing Raptor Rescue Center in 2018–2020. This rescue center is located in eastern China, on a major migratory route for raptors in East Asia. We identified the sex of 646 individuals (belonging to 29 species) using two sets of primers, and analyzed the sex ratios of five species with a sample size >30 individuals. Generally, the sex ratios differed among species: the sex ratio of Eurasian Kestrels (Falco tinnunculus) was skewed toward males (P = 0.006), while the sex ratio of Eurasian Sparrowhawks (Accipiter nisus) was skewed toward females (P = 0.024). The sex ratio of Long-eared Owls (Asio otus) tended to be female-biased (P = 0.058). There was no significant bias of sex ratio in Oriental Scops-Owls (Otus sunia) or Amur Falcons (Falco amurensis). We discussed several possible reasons that could drive the biased sex ratios of raptors brought into rehabilitation centers. Our findings could be helpful for future studies on sex identification of raptors and conservation efforts.

Blakiston's Fish Owl (also known as Blakiston's Eagle-Owl; Bubo blakistoni) is an endangered species that inhabits northeast Asia. Blakiston's Fish Owls were rare (approximately 70 individuals) on Hokkaidō, Japan, at the start of my study, but rigorous protection and intervention programs have led to more than a doubling of the population (approximately 165 individuals) since 1970. Despite its elusive nature and rarity, I have studied this owl species by direct observation and banding for 46 yr throughout Hokkaidō. I here report on little known aspects of its intraspecific interactions and breeding behavior (specifically, pair formation). Identification of individual birds was facilitated by color-banding (a total of 447 owls from 1985–2019). Most pair formations began with an individual male or female flying into the territory of a single owl of the opposite sex, duetting with the resident owl, and then the pair flying together through the forest. However, pair formation occasionally occurred by displacement of a member of an established pair; in some cases, a replacement male took over parental duties. Under government permit, I cared for injured owls, which were housed in large outdoor aviaries; these captive owls sometimes attempted to form pair bonds with wild birds in the area. To test the feasibility of “matchmaking” to increase the number of territorial pairs on Hokkaidō, I attempted to induce pairing of releasable captive birds with wild birds, or to release them into territories with single adults; these tests resulted in successful pair-bonding of the target birds in two cases. I here describe these observations of intraspecific interactions and pair formation to aid future conservation efforts for this endangered species.