Single Perch Research Articles

A Sarrus-Based Passive Mechanism for Rotorcraft Perching

This work examines a passive perching mechanism that enables a rotorcraft to grip branchlike perches and resist external wind disturbance using only the weight of the rotorcraft to maintain the grip. We provide an analysis of the mechanism’s kinematics, present the static force equations that describe how the weight of the rotorcraft is converted into grip force onto a cylindrical perch, and describe how grip forces relate to the ability to reject horizontal disturbance forces. The mechanism is optimized for a single perch size and then for a range of perch sizes. We conclude by constructing a prototype mechanism and demonstrate its use with a remote-controlled (RC) helicopter.

Vigilance and roosting behaviour of laying hens on different perch heights

Laying hens prefer roosting on high compared to low perches during night time. According to the antipredator hypothesis, hens on high perches can afford to be less vigilant while roosting at night. A total of 120 LSL hens in groups of five were presented a single perch, which was varied in height throughout two subsequent experiments each. In experiment 1, an acoustic noise was played back in the middle of the night. Hens’ latencies until reaction and their roosting behaviours shown before disturbance were analysed depending on perch height (30, 90, or 150cm). In addition, roosting behaviours were recorded throughout the entire experimental nights and differences were analysed in relation to perch height. Experiment 2 focussed on night-time use of single perches offered at ten different heights ranging from 20cm to 180cm. In experiment 1, perch height and hens’ body orientation towards the source of acoustic noise did not influence reaction latencies (P>0.05). Surprisingly, hens resting with their head forward immediately before playbacks showed a slower reaction (LS-means=1.27s) to the acoustic noise than hens resting with their head under the wing (LS-means=0.71s, P=0.004). In contrast, the percentage of hens perching with their head forward during the entire night was higher on low (LS-means=55.48%) compared to high perches (LS-means=33.44%, P=0.001) in experiment 1. In both experiments, perch use increased with rising height up to 90cm. In experiment 2, hens did not show a preference for roosting on the perch compared to resting on the floor at a perch height of 80cm or lower. Although hens showed a clear preference to roost on perches higher than 90cm, their reactions to an acoustic disturbance during night time did not clearly support the antipredator hypothesis. Possibly, perch height may be a crucial factor when hens are searching for an appropriate roosting place before the dark period but may have limited influence on roosting behaviour during the night.

Perch Arrangements in Small-Group Furnished Cages for Laying Hens

In 2 trials, including 2,768 birds in total, 3 different perch arrangements were evaluated in furnished 8-hen cages for laying hens. The hybrids used were Lohmann Selected Leghorn and Lohmann Brown in trial 1 and Hy-Line White and Hy-Line Brown in trial 2. The furnished cages were identical in all other respects than the arrangement of perches. A perch was either fitted across the cage, providing 12 cm of perch per hen, or 2 perches were installed in a cross, implying 15 cm per hen. Although the perches arranged in a cross provided more perch per hen than the single perch fitted across the cage, perch use at night by the birds was similar or lower as compared with the single perch. Hence, the way perches are arranged in the cage may be as important as perch length itself to achieve a high use at night. Perch arrangement did not affect production, mortality, or egg quality. Compared with a conventional battery cage, also included in the trials, hygiene was inferior in the furnished cages, but there was no difference in proportions of dirty eggs. Differences in proportions of cracked eggs were found between furnished and conventional cages in 1 of the trials. However, on the whole, production, mortality, and egg quality were at similar levels in all cage models. Genotype differences were found in production traits, egg quality, hygiene, and in the use of perches and nests.

Individual, Sexual, Seasonal, and Temporal Variation in the Amount of Sagebrush Lizard Scent Marks

Although many animals deposit scent marks, previous studies have focused almost entirely on rodents or on the chemical structure of the signal. Here, we study the quantity and temporal pattern of chemical deposition by the territorial sagebrush lizard Sceloporus graciosus, measuring both femoral pore and fecal deposits. Specifically, we tested whether variation in deposition is a good cue of individual and sexual identity and/or whether it is more closely associated with body size and reproductive state, indicators of physiological condition. The results support the latter hypothesis. We found that although the amount of fluid deposited on a single perch (rarely quantified in mammals) carries little information on individual or sexual identity, it reflects the physiological condition and reproductive state of individual lizards and is replenished on a roughly weekly cycle, potentially providing additional information on the producer's activity level. The amount of deposition may thus provide important information to chemical receivers making mate choice and territorial defense decisions. The results further suggest that seasonal increases in gland production allow lizards to mark more sites rather than to influence the quality of the signal on a single perch.

The choice of arboreal escape paths and its consequences for the locomotor behaviour of four species of Anolis lizards

The direction and speed of escape locomotion can affect the ability of an animal to evade a predator, and variation in habitat structure often affects speed. Consequently, the escape paths chosen by animals may affect their performance and subsequent survival. Arboreal locomotion is well suited for gaining insight into the choice of escape routes because of the discrete paths formed by branches. Decreased branch diameter and increased angles between branches can significantly decrease locomotor speeds, but no previous study has determined whether arboreal lizards selectively choose alternative paths. We quantified choice of escape paths and locomotor performance of four syntopic species of arboreal Anolis lizards in their natural habitat and in the laboratory. In the field, species with shorter limbs occurred more commonly on narrow perches than did long-limbed species, but all species favoured escape paths with larger-diameter perches and straighter interperch angles. Thus, short-limbed species used narrower perches than long-limbed species merely as a result of what they encountered, rather than as a result of a biased choice at branching points. In natural vegetation, choosing branches with the largest diameter often results in the straightest path. However, in the laboratory, most lizards preferred large-diameter perches with a sharp turn to continuing a straight path onto a small-diameter perch. Although an overriding preference for larger perch diameter may optimize escape speed within a single perch, a maladaptive side-effect could be a compromise of the overall rate of gaining distance from starting points in paths with turns.

Site fidelity of mariametrid crinoids (Echinodermata: Crinoidea) in southeast Sulawesi, Indonesia

Unstalked crinoids, or feather stars, in the family Mariametridae are nocturnal filter feeders commonly found on tropical Indo-west Pacific coral reefs. They are more mobile than other feather star groups, though they are normally attached to the substratum with their cirri and/or arms. Mariametrids usually crawl using their arms (Fishelson 1974), but can also swim short distances (Zmarzly 1985; Stevens 1989). During the day they hide within crevices in the reef and only emerge at dusk to their nocturnal feeding perch. Most non-mariametrid crinoids may be active at various times throughout the diel cycle. Their feeding postures are related to current regimes rather than day– night cycles (Meyer et al. 1984), and they do not move to and from feeding perches. Anecdotal observations indicate that diel-active crinoids can remain on a single perch for long periods of time. Accounts of up to 2 years occupancy are known (Stevens 1989), although a single 5-year residence has been reported (Meyer 1973a). Zmarzly (1984) quantified site fidelity in diel-active crinoids over 6 months with all specimens remaining on their original perches with no observable mortality, emigration, or recruitment. Meyer et al. (1984) used time-lapse cinematography to observe crinoid posture in relation to current. Two mariametrids were observed during the study, and each individual used a different route to reach and exit its nocturnal perch. No information was given about whether individuals displayed any site fidelity, despite the film covering two day–night cycles. The ability to return to a site after a period of absence has never been examined. Although crinoids are sensitive to photic, mechanical and chemical stimuli, they apparently lack sense organs sensu stricto (Heinzeller and Welsch 1994). The recent discovery of specific photosensory organs in similarly light-sensitive brittlestars (Aizenberg et al. 2001) opens debate about homologous sensory systems in their crinoid relatives. There is no doubt that mariametrids leave their nocturnal feeding perch during daylight hours. If they are able to consistently return to the same feeding perches over long periods of time, it raises interesting questions about the mechanisms they utilize to do so. This study investigates the temporal distribution and short-term site fidelity of individual mariametrid crinoids on a shallow coral reef system.

Group foraging versus solitary foraging efficiency in piscivorous predators: the perch, Perca fluviatilis, and pike, Esox lucius, patterns

A predator's foraging strategy is generally described as either a sit-and-wait or an actively searching strategy. Two different behaviour patterns, often associated with these strategies, are territorial behaviour for a sit-and-wait predator, and group foraging behaviour for an actively searching predator. In a pond experiment, the effect of predator density on the efficiency of a sit-and-wait predator, pike, and an actively searching predator, perch, was tested. The foraging efficiencies of these two predators were predicted to be density-dependent since perch is a social species with its efficiency enhanced by mutualistic interactions, while pike is a territorial species with its efficiency reduced by competitive interactions. The predators were stocked at two densities (one or five individuals) in enclosures containing the same prey densities (75 individuals of juvenile perch). The behaviour of predators and prey, prey mortality and predator growth were studied. As expected, swimming speed and move frequency were significantly higher for perch than for pike. In the five-pike treatment, predator activity (swimming speed and move frequency) was highly size-dependent with the large pike both swimming faster and moving more frequently than the small pike. The activity levels of the pike were also reflected in the area used, which was larger for the large pike. Perch at both densities and the large pike used similar areas. As hypothesized, the growth rate of the predators corresponded to their foraging strategies. The growth rate of group foraging perch was higher than that of single perch and pike in both density treatments. In the single predator treatments, pike grew better than perch. In contrast to perch, the single pike grew more than the five pike together.