N.P. Lester

Bio: N.P. Lester is an academic researcher from University of Sussex. The author has an hindex of 1, co-authored 1 publications receiving 166 citations.

Minimising Errors in Splitting Behaviour Into Bouts

Abstract: Some problems in using log survivor functions to split behaviour into bouts are outlined. It is argued that it is usually best to choose that bout criterion which leads to the fewest within and between bout intervals being assigned to the wrong category. A way of doing this is illustrated and other possible criteria are considered. The influence of misassignment on data analysis is discussed and it is argued that where this is substantial analysis in terms of bouts may not be useful.

The Behavioral Ecology of Intermittent Locomotion1

Abstract: Most physiological and ecological approaches to animal locomotion are based on steady state assumptions, yet movements of many animals are interspersed with pauses lasting from milliseconds to minutes. Thus, pauses, along with changes in the duration and speed of moves, form part of a dynamic system of intermittent locomotion by which animals adjust their locomotor behavior to changing circumstances. Intermittent locomotion occurs in a wide array of organisms from protozoans to mammals. It is found in aerial, aquatic and terrestrial locomotion and in many behavioral contexts including search and pursuit of prey, mate search, escape from predators, habitat assessment and general travel. In our survey, animals exhibiting intermittent locomotion paused on average nearly 50% of their locomotion time (range 6–94%). Although intermittent locomotion is usually expected to increase energetic costs as a result of additional expenditure for acceleration and deceleration, a variety of energetic benefits can arise when forward movement continues during pauses. Endurance also can be improved by partial recovery from fatigue during pauses. Perceptual benefits can arise because pauses increase the capacity of the sensory systems to detect relevant stimuli. Several processes, including velocity blur, relative motion detection, foveation, attention and interference between sensory systems are probably involved. In animals that do not pause, alternative mechanisms for stabilizing the perceptual field are often present. Because movement is an important cue for stimulus detection, pauses can also reduce unwanted detection by an organism's predators or prey. Several models have attempted to integrate energetic and perceptual processes, but many challenges remain. Future advances will require improved quantification of the effects of speed on perception.

Movement parameters of ungulates and scale‐specific responses to the environment

Abstract: Summary 1. Most studies of animal movements and habitat selection do not recognize empirically that different components of the environment are important to animals at different scales. Often, availability of habitats is defined at one or more arbitrary spatio-temporal scales, but use of those habitats is constrained to one scale. Identification of scalar movement is the first step in developing models to explain why animals select or move to certain parts of their range. We used a non-linear curve-fitting model of movement rates to identify discontinuities in the scales of movement by woodland caribou Rangifer tarandus caribou collared with global positioning system (GPS) collars. 2. We differentiated intrapatch from interpatch movements, but were unable to distinguish interpatch from migratory-type movements for most combinations of individual caribou by season. Model fit was stronger for winter than summer movements. We suggest that increased patch heterogeneity during the winter resulted in interseason variation in movements and corresponding model fit. 3. Responses by caribou to the environment were scale-dependent. When we applied logistic regressions, land-cover type, energetic costs of movement, and predation risk differentiated the two scales of movement. Intrapatch movements had a lower cost of movement, were associated with cover types where foraging behaviours probably occurred, and were closer to areas of higher predator risk than interpatch movements. 4. Application of the non-linear model will aid in developing mechanism-based approaches to studying resource selection and animal behaviour.

Foraging behaviour of Antarctic fur seals during periods of contrasting prey abundance

Abstract: 1. Foraging behaviour of Antarctic fur seals rearing pups at Bird Island, South Georgia, was assessed using at-sea activity patterns measured by electronic time-depth recorders. Information was obtained for a total of 75 individuals and 191 foraging trips to sea over five reproductive seasons from 1988/89 to 1992/93; this included one season (1990/91) of low prey abundance. A method was developed to divide the diving record up into logical units or bouts which differed from past methods used for defining bouts of behaviour. 2. Foraging trips were significantly longer in 1990/91 than in the other years. There were significant differences between years in the proportion of time spent foraging when at sea and in the distribution of foraging through the day and night. These differences probably represent behavioural responses to changes in prey distribution and abundance and were reflected in the frequency of occurrence of different types of foraging behaviour. 3. Four types of foraging bout were recognized using a cluster analysis. Type I (short) bouts were of short duration (17 min) and occurred mainly during daytime and at dusk. They probably represented exploratory behaviour. Type II (long) bouts occurred mainly at night and were of long duration (80 min). They increased in frequency in 1990/91 when food was scarce and 61-73% of time spent foraging was in these bouts. Type III (shallow) bouts occurred mainly at night, were of short duration (12 min) and represented feeding close to the surface, possibly in association with other, surface-feeding krill predators. Shallow bouts accounted for 8-14% of time spent foraging. Type IV (deep) bouts were of medium duration (19 min) and represented feeding at greater depth (40-50 m) than other bout types. They were most abundant around dawn. 4. Mean dive duration during bouts exceeded the theoretical aerobic dive limit on > 30% of occasions for short, long and deep bouts. There were positive correlations between mean dive duration and surface interval duration for most of these bout types in most years. This suggested that long dives incurred a cost in terms of the amount of time spent at the surface between dives. 5. The study demonstrated that female fur seals invest a significantly greater effort in foraging during periods of low prey abundance by both increasing the time spent foraging and by increasing activity during foraging. This could represent a 30-50% increase in the costs of foraging during years of low food abundance.

Mushroom Bodies Suppress Locomotor Activity in Drosophila melanogaster

Abstract: Locomotor activity of single, freely walking flies in small tubes is analyzed in the time domain of several hours. To assess the influence of the mushroom bodies on walking activity, three independent noninvasive methods interfering with mushroom body function are applied: chemical ablation of the mushroom body precursor cells; a mutant affecting Kenyon cell differentiation (mushroom body miniature); and the targeted expression of the catalytic subunit of tetanus toxin in subsets of Kenyon cells. All groups of flies with mushroom body defects show an elevated level of total walking activity. This increase is attributable to the slower and less complete attenuation of activity during the experiment. Walking activity in normal and mushroom body-deficient flies is clustered in active phases (bouts) and rest periods (pauses). Neither the initiation nor the internal structure, but solely the termination of bouts seems to be affected by the mushroom body defects. How this finding relates to the well-documented role of the mushroom bodies in olfactory learning and memory remains to be understood.