High-speed Pursuits Research Articles

Dual Receptive Fields Underlying Target and Wide-Field Motion Sensitivity in Looming-Sensitive Descending Neurons.

Responding rapidly to visual stimuli is fundamental for many animals. For example, predatory birds and insects alike have amazing target detection abilities, with incredibly short neural and behavioral delays, enabling efficient prey capture. Similarly, looming objects need to be rapidly avoided to ensure immediate survival, as these could represent approaching predators. Male Eristalis tenax hoverflies are nonpredatory, highly territorial insects that perform high-speed pursuits of conspecifics and other territorial intruders. During the initial stages of the pursuit, the retinal projection of the target is very small, but this grows to a larger object before physical interaction. Supporting such behaviors, E. tenax and other insects have both target-tuned and loom-sensitive neurons in the optic lobes and the descending pathways. We here show that these visual stimuli are not necessarily encoded in parallel. Indeed, we describe a class of descending neurons that respond to small targets, to looming and to wide-field stimuli. We show that these descending neurons have two distinct receptive fields where the dorsal receptive field is sensitive to the motion of small targets and the ventral receptive field responds to larger objects or wide-field stimuli. Our data suggest that the two receptive fields have different presynaptic input, where the inputs are not linearly summed. This novel and unique arrangement could support different behaviors, including obstacle avoidance, flower landing, and target pursuit or capture.

Hoverfly (Eristalis tenax) pursuit of artificial targets.

The ability to visualize small moving objects is vital for the survival of many animals, as these could represent predators or prey. For example, predatory insects, including dragonflies, robber flies and killer flies, perform elegant, high-speed pursuits of both biological and artificial targets. Many non-predatory insects, including male hoverflies and blowflies, also pursue targets during territorial or courtship interactions. To date, most hoverfly pursuits have been studied outdoors. To investigate hoverfly (Eristalis tenax) pursuits under more controlled settings, we constructed an indoor arena that was large enough to encourage naturalistic behavior. We presented artificial beads of different sizes, moving at different speeds, and filmed pursuits with two cameras, allowing subsequent 3D reconstruction of the hoverfly and bead position as a function of time. We show that male E. tenax hoverflies are unlikely to use strict heuristic rules based on angular size or speed to determine when to start pursuit, at least in our indoor setting. We found that hoverflies pursued faster beads when the trajectory involved flying downwards towards the bead. Furthermore, we show that target pursuit behavior can be broken down into two stages. In the first stage, the hoverfly attempts to rapidly decreases the distance to the target by intercepting it at high speed. During the second stage, the hoverfly's forward speed is correlated with the speed of the bead, so that the hoverfly remains close, but without catching it. This may be similar to dragonfly shadowing behavior, previously coined 'motion camouflage'.

Habitat thresholds for successful predation under landscape change

ContextHabitat loss and alteration affect wildlife populations worldwide. Bush encroachment alters landscapes and threatens arid and semi-arid grasslands, but its effects on predator–prey relationships and carnivore community ecology are not well understood. Predation strategies of large predators, for example high-speed pursuits versus ambush from short distances, are likely to be affected differently by bush encroachment.ObjectivesWe assessed how bush encroachment affects overall predation success of cheetahs (Acinonyx jubatus) and leopards (Panthera pardus) in a savanna landscape under variable fractional woody cover (FWC). We tested if predation success remained relatively unchanged for leopards across a gradient of FWC, and whether cheetah predation was most successful at low to intermediate cover and varied seasonally.MethodsBelly scores of predators were measured from camera-trap images collected over 7 years in north-central Namibia and used to index predation success. We derived predicted belly score probabilities as a function of FWC, which was measured using a Synthetic Aperture Radar (SAR)-derived satellite data layer.ResultsPredicted leopard predation success was highest at 0.27–0.34 FWC in the dry season, potentially due to lower prey density in highly covered areas and decreased prey catchability in low cover. Predicted cheetah predation success was highest at 0.24–0.28 FWC in the wet season, potentially due to increased landscape openness, high availability of habitat margins for visualising and stalking prey, and decreased kleptoparasitism by leopards. These results highlight optimal habitat cover thresholds that favour lower FWC for cheetah than for leopard.ConclusionsThe findings indicate that landscape heterogeneity is important for predation success of cheetahs and leopards, suggesting that habitat management should focus on bush control efforts to maintain intermediate levels of bush cover.

A Longitudinal Examination of Officer Deaths from Vehicle Pursuits

Little research has examined the changing dangerousness of police high-speed pursuits over time, especially with regard to the safety of the officer. Using data from all pursuit-related officer deaths in the USA between 1960 and 2011, this study tested the hypothesis that the officer death rate has been decreasing. Least-squares lines were calculated through the data point of each year to estimate trends in officer death rates over time. The findings revealed that the death rate for officers directly involved in pursuits has decreased steadily, as has the death rate for officers manning roadblocks. The death rate for officers deploying spike strips or travelling to assist in the pursuit, however, has been steadily increasing. The findings suggest further development of pursuit policies to address these issues.

Terrestrial predation by polar bears: not just a wild goose chase

Behavioral predictions based on optimal foraging models that assume an energy-maximizing strategy have been challenged on both theoretical and empirical grounds. Although polar bears (Ursus maritimus) are specialist predators of seal pups on the Arctic ice pack, the use of terrestrial food sources during the ice-free period has received increased attention in recent years in light of climate predictions. Across a 10-day period of observation, we documented between four and six individual polar bears successfully capture at least nine flightless lesser snow geese (Chen caerulescens caerulescens) and engage in at least eight high-speed pursuits of geese. The observed predatory behaviors of polar bears do not support predictions made by energy-optimizing foraging models and suggest that polar bears may frequently engage in energy inefficient pursuits of terrestrial prey. Further study of the nutritional needs and foraging behaviors of polar bears during the ice-free period is warranted, given that polar bears are predicted to spend more time on land as climate change advances.

Recent Legal Developments

This article provides an assessment of the U.S. Supreme Court's decision in Scott v. Harris (2007). The assessment provides students, criminal justice scholars, and practitioners with an overview of the current status of case law on police pursuits. Since the 1980s, police pursuits have emerged as a high-profile liability area due to their risk of danger and injury or death to a suspect, officers, and innocent third parties (Alpert, 1998; Gallagher, 1989; Hill, 2002; Kappeler, 2006; Kappeler, Kappeler, & del Carmen, 2001; O'Connor & Norse, 2006; Ross & Bodapoti, 2006). The Scott decision marks the third decision since 1989 in which the topic of police pursuits has been addressed by the Court. The article reviews the Court's prior decisions on the subject, provides an analysis of Scott, and examines how lower courts have applied the decision to high-speed police pursuits.

A Review of Police Pursuit Fatalities in the United States From 1982–2004

Background. High-speed police pursuits are common in the United States (US). Most states do not gather statistics on police pursuits, pursuit crashes, injuries or fatalities for annual review. Objective. The objective of this study is to determine the number of pursuit fatalities to officers, those in the chased vehicle, andthose uninvolved in pursuits from 1982–2004. Methods. A review of police pursuit fatalities reported to the National Highway Traffic Safety Administration (NHTSA) Fatality Analysis Reporting System (FARS) database from 1982–2004. The data was reviewed for fatalities, demographic data, alcohol involvement, road surface type (rural versus urban) andmechanism of collision leading to a pursuit fatality. Results. From 1982–2004, 881,733 fatal crashes were reported to NHTSA, leading to 987,523 fatalities. Of fatal crashes, 6,336 (0.7%) were secondary to pursuits, leading to 7,430 (0.8%) fatalities, a mean of 323 per year. Among these fatalities, chased vehicle occupants accounted for 5,355 (72%); police for 81 (1%); those uninvolved for 1994 (27%). Of fatalities, 6074 (82%) were male, 2,092 (28%) were children andadolescents. Mean age of death was 24 years. African–Americans 1,154 (24%) andNative Americans 101 (2%) died at a higher proportion than their percentage of the US population. Collisions with solid objects accounted for 3,175 (59%) of fatalities in the chased vehicles. Collisions with other moving vehicles accounted for 1,434 (80%) of fatalities of vehicular occupants uninvolved in pursuits. Most fatal crashes, 3,130 (62%), occurred on urban roadways. Alcohol was involved in 4,628 (62%) fatalities. Of police fatalities, 20 (25%) were intoxicated. Conclusions. Police pursuits results in a small yet significant number of fatal motor vehicular crashes andfatalities. All states should record the total number of police pursuits, pursuit crashes, injuries andfatalities for annual review. The findings in this study have important operational implications for EMS care.

The Phantom of Deterrence: The Crime (Serious and Repeat Offenders) Sentencing Act

Throughout 1991 a car theft “crime wave” and a series of deaths arising from high-speed police pursuits had engendered an atmosphere of crisis in “law and order” in Western Australia. Prompted by these events, controversial legislation (the Crime (Serious and Repeat Offenders) Sentencing Act 1992) aimed at “high risk” juvenile offenders and increasing penalties was rushed through the Parliament of Western Australia in early 1992. A critique of the legislation illustrates that it both breached human rights and failed to address the difficulties of implementing selective incapacitation policies. Following the introduction of the new law the government claimed that downward trends in car theft, police high-speed pursuits and other offences were due to the deterrent effects of the increased penalties provided. The data, however, indicate that the decline in official records of car theft and juvenile convictions had begun prior to the introduction of the legislation. Significant correlations between reports of stolen vehicles and arrests for car theft (especially Aboriginal juvenile arrests) were found but not for police high-speed pursuits or arrests of persistent offenders and reports of stolen vehicles. This suggests that targeting “hard core” juvenile offenders had, at best, modest and temporary effects on vehicle theft. While a sharp decline in the relevant statistics was observed around the time of the passage of the law, this proved short-lived and other factors, such as changes in policing (the introduction of cautioning, the formation of a special motor vehicle task force, and stricter guidelines on pursuits) are more compelling explanations than the deterrent aims of the legislation.