Hawk Parabuteo Unicinctus Research Articles

HawkEar: A bird‐borne visual and acoustic platform for eavesdropping the behaviour of mobile animals

Abstract Unoccupied aerial vehicles (UAVs; drones) offer mobile platforms for ecological investigation, but can be impractical in some environments and the resulting noise can disturb wildlife. We developed a mobile alternative using a bird‐borne platform to record the behaviour of other animals in the field. This unit consists of a lightweight audio and video sensor that is carried by a trained Harris's hawk Parabuteo unicinctus. We tested the hypothesis that our bird‐borne platform is a viable option for collecting behavioural data from mobile animals. We recorded acoustic and video data as the hawk flew through a dense group of Brazilian free‐tailed bats Tadarida brasiliensis emerging from a cave, with a test case of investigating how echolocation calls change depending on spatial position in the bat group. The HawkEar platform is an alternative for collecting behavioural data when a mobile platform that is less noisy and restrictive than traditional UAVs is needed. The design and software are open source and can be modified to accommodate additional sensor needs.

Obstacle avoidance in aerial pursuit

Pursuing prey through clutter is a complex and risky activity requiring integration of guidance subsystems for obstacle avoidance and target pursuit. The unobstructed pursuit trajectories of Harris' hawks Parabuteo unicinctus are well modeled by a mixed guidance law feeding back target deviation angle and line-of-sight rate. Here we ask how their pursuit behavior is modified in response to obstacles, using high-speed motion capture to reconstruct flight trajectories recorded during obstructed pursuit of maneuvering targets.We find that Harris' hawks use the same mixed guidance law during obstructed pursuit but appear to superpose a discrete bias command that resets their flight direction to aim at a clearance of approximately one wing length from an upcoming obstacle as they reach some threshold distance from it. Combining a feedback command in response to target motion with a feedforward command in response to upcoming obstacles provides an effective means of prioritizing obstacle avoidance while remaining locked-on to a target. We therefore anticipate that a similar mechanism may be used in terrestrial and aquatic pursuit. The same biased guidance law could also be used for obstacle avoidance in dronesdesigned to intercept other drones in clutter, or to navigate between fixed waypoints in urban environments.

Visual versus visual-inertial guidance in hawks pursuing terrestrial targets.

The aerial interception behaviour of falcons is well modelled by a guidance law called proportional navigation, which commands steering at a rate proportional to the angular rate of the line-of-sight from predator to prey. Because the line-of-sight rate is defined in an inertial frame of reference, proportional navigation must be implemented using visual-inertial sensor fusion. By contrast, the aerial pursuit behaviour of hawks chasing terrestrial targets is better modelled by a mixed guidance law combining information on the line-of-sight rate with information on the deviation angle between the attacker's velocity and the line-of-sight. Here we ask whether this behaviour may be controlled using visual information alone. We use high-speed motion capture to record n = 228 flights from N = 4 Harris' hawks Parabuteo unicinctus, and show that proportional navigation and mixed guidance both model their trajectories well. The mixed guidance law also models the data closely when visual-inertial information on the line-of-sight rate is replaced by visual information on the motion of the target relative to its background. Although the visual-inertial form of the mixed guidance law provides the closest fit, all three guidance laws provide an adequate phenomenological model of the behavioural data, whilst making different predictions on the physiological pathways involved.

What makes an urban raptor?

Raptor communities are negatively impacted by urbanization. However, some species can thrive in urban areas. Raptor species traits that favour their presence in urban areas have been scarcely studied. Moreover, phylogenetic relatedness may be a factor promoting raptor occurrence in urban areas. In this study, we use data gathered through citizen science in Argentina to analyse the phylogenetic signal and the drivers that correlate with raptor presence in urban settings. The mean percentage urban cover for the records of each species was considered as an index of raptor occurrence in urban areas. A total of 55 species were analysed, which accounted for 90% of the diurnal raptors of Argentina. Harris’s Hawk Parabuteo unicinctus, Pearl Kite Gampsonyx swainsonii and Chimango Caracara Milvago chimango had the highest urban index. Raptor occurrence in urban areas had a marginal phylogenetic signal, indicating a tendency for more closely related species to have similar tolerances to urbanization. The index of raptor occurrence in urban areas was highest for the most common species of non‐urban areas, and was not related to traits such as body mass, diet, nesting site and migratory behaviour. Our results highlight the importance of citizen science projects in data gathering at large geographical scales.

West Nile virus outbreak in captive and wild raptors, Czech Republic, 2018

West Nile virus lineage 2 (WNV-2) was detected in the brain of 17 goshawks (Accipiter gentilis) that succumbed to neuroinvasive disease in the Czech Republic during 2018: twelve birds were captive and five wild. Furthermore, two wild sparrowhawks (Accipiter nisus) and three other captive birds of prey (golden eagle Aquila chrysaetos, hybrid saker falcon Falco cherrug×F. rusticolus and Harris's hawk Parabuteo unicinctus) also died due to WNV encephalitis. The 2018 outbreak in Czech raptors clearly reflects a new epidemiological situation and indicates an increasing risk of both raptor and human infection with WNV-2 in the country.

Hawks steer attacks using a guidance system tuned for closepursuit of erratically manoeuvring\xa0targets

Aerial predators adopt a variety of different hunting styles, withdivergent flight morphologies typically adapted either to high-speed interception ormanoeuvring through clutter, but how are their sensorimotor systems tuned inrelation to habitat structure and prey behavior? Falcons intercept prey athigh-speed using the same proportional navigation guidance law as homing missiles.This classical guidance law works well in the open, but performs sub-optimallyagainst highly-manoeuvrable targets, and may not produce a feasible path through thecluttered environments frequented by hawks and other raptors. Here we identify theguidance law of n = 5 Harris’ Hawks Parabuteo unicinctus chasing erratically manoeuvringartificial targets. Harris’ Hawks use a mixed guidance law, coupling low-gainproportional navigation with a low-gain proportional pursuit element. This guidancelaw promotes tail-chasing and is not thrown off by erratic manoeuvres, making itwell suited to the hawks’ natural hunting style, involving close pursuit of agileprey through clutter.

Exploring the relationship between flapping behaviour and accelerometer signal during ascending flight, and a new approach to calibration

We understand little about the energetic costs of flight in free‐ranging birds, in part because current techniques for estimating flight energetics in the wild are limited. Accelerometry is known to estimate energy expenditure through body movement in terrestrial animals, once calibrated using a treadmill with chamber respirometry. The flight equivalent, a wind tunnel with mask respirometry, is particularly difficult to instigate, and has not been applied to calibrate accelerometry. We take the first steps in exploring a novel method for calibrating accelerometers with flight energy expenditure. We collected accelerometry data for Harris's Hawks Parabuteo unicinctus flying to varying heights up to 4.1 m over a small horizontal distance; the mechanical energy expended to gain height can be estimated from physical first principles. The relationship between accelerometry and mechanical energy expenditure was strong, and while a simple wing flapping model confirmed that accelerometry is sensitive to both changes in wing beat amplitude and frequency, the relationship was explained predominately by changes in wing beat frequency, and less so by changes in amplitude. Our study provides initial, positive evidence that accelerometry can be calibrated with body power using climbing flights, potentially providing a basis for estimating flapping flight metabolic rate at least in situations of altitude gain.

How fast can raptors see?

Birds, and especially raptors, are highly visual animals. Some of them have the highest spatial resolving power known in the animal kingdom, allowing prey detection at distance. While many raptors visually track fast-moving and manoeuvrable prey, requiring high temporal resolution, this aspect of their visual system has never been studied before. In this study, we estimated how fast raptors can see, by measuring the flicker fusion frequency of three species with different lifestyles. We found that flicker fusion frequency differed among species, being at least 129 Hz in the peregrine falcon, Falco peregrinus, 102 Hz in the saker falcon, Falco cherrug, and 81 Hz in the Harris's hawk, Parabuteo unicinctus We suggest a potential link between fast vision and hunting strategy, with high temporal resolution in the fast-flying falcons that chase fast-moving, manoeuvrable prey and a lower resolution in the Harris's hawk, which flies more slowly and targets slower prey.

High resolution of colour vision, but low contrast sensitivity in a diurnal raptor.

Animals are thought to use achromatic signals to detect small (or distant) objects and chromatic signals for large (or nearby) objects. While the spatial resolution of the achromatic channel has been widely studied, the spatial resolution of the chromatic channel has rarely been estimated. Using an operant conditioning method, we determined (i) the achromatic contrast sensitivity function and (ii) the spatial resolution of the chromatic channel of a diurnal raptor, the Harris's hawk Parabuteo unicinctus The maximal spatial resolution for achromatic gratings was 62.3 c deg-1, but the contrast sensitivity was relatively low (10.8-12.7). The spatial resolution for isoluminant red-green gratings was 21.6 c deg-1-lower than that of the achromatic channel, but the highest found in the animal kingdom to date. Our study reveals that Harris's hawks have high spatial resolving power for both achromatic and chromatic vision, suggesting the importance of colour vision for foraging. By contrast, similar to other bird species, Harris's hawks have low contrast sensitivity possibly suggesting a trade-off with chromatic sensitivity. The result is interesting in the light of the recent finding that double cones-thought to mediate high-resolution vision in birds-are absent in the central fovea of raptors.

Rare birds in Slovenia in 2015 – Slovenian Rarities Committee’s Report

Summary This report by the Slovenian Rarities Committee presents records of rare bird species in Slovenia in 2015, with some addenda for previous years. The numbers in brackets refer to the number of records (first number) and individuals (second number) recorded between 1 Jan 1950 and 31 Dec 2014. Since 1 Jan 2013, submission to the Committee has been required for 37 additional species, 17 of which are regional rarities. Records of these species are not numbered, since records from previous years were not collected by the Committee. One new species, the Desert Wheatear Oenanthe deserti, was added to category A. Other notable observations were the first record of Parrot Crossbill Loxia pytyopsittacus after 1909, the second record of Baillon’s Crake Zapornia pusilla, the third and fourth records of Calandra Lark Melanocorypha calandra, the fourth of Long-legged Buzzard Buteo rufinus, the fifth of Richard’s Pipit Anthus richardi and the sixth of Grey Phalarope Phalaropus fulicarius. Four species were added to category E: Bahama Pintail Anas bahamensis, Rosy-billed Pochard Netta peposaca, Harris’s Hawk Parabuteo unicinctus and Alexandrine Parakeet Psittacula eupatria. The list of birds recorded in Slovenia (as of 31 Dec 2015) contains 386 species (371 in category A, 6 in category B, 9 exclusively in category C; 4 species are both in categories A and C). Category D contains 6 species, while category E contains 38, two of which are classified into subcategory E*. These two categories are not part of the list.

Visual abilities in two raptors with different ecology.

Differences in visual capabilities are known to reflect differences in foraging behaviour even among closely related species. Among birds, the foraging of diurnal raptors is assumed to be guided mainly by vision but their foraging tactics include both scavenging upon immobile prey and the aerial pursuit of highly mobile prey. We studied how visual capabilities differ between two diurnal raptor species of similar size: Harris's hawks, Parabuteo unicinctus, which take mobile prey, and black kites, Milvus migrans, which are primarily carrion eaters. We measured visual acuity, foveal characteristics and visual fields in both species. Visual acuity was determined using a behavioural training technique; foveal characteristics were determined using ultra-high resolution spectral-domain optical coherence tomography (OCT); and visual field parameters were determined using an ophthalmoscopic reflex technique. We found that these two raptors differ in their visual capacities. Harris's hawks have a visual acuity slightly higher than that of black kites. Among the five Harris's hawks tested, individuals with higher estimated visual acuity made more horizontal head movements before making a decision. This may reflect an increase in the use of monocular vision. Harris's hawks have two foveas (one central and one temporal), while black kites have only one central fovea and a temporal area. Black kites have a wider visual field than Harris's hawks. This may facilitate the detection of conspecifics when they are scavenging. These differences in the visual capabilities of these two raptors may reflect differences in the perceptual demands of their foraging behaviours.

String-pulling behaviour in a Harris's HawkParabuteo unicinctus

Variations on the string-pull experiment have been presented to a variety of avian species. Here, we present the results of a basic vertical string-pull task with a Harris's Hawk Parabuteo unicinctus. A 2-year-old subject retrieved a shielded food reward within 8 min on each of eight trials and spontaneously used solving techniques similar to corvids and parrots. Our data contribute to the small body of literature on raptor cognition by showing that it may be within the realm of at least one bird of prey species to perform the string-pull task similarly to avian species renowned for their high cognitive abilities.