Perch Selection Research Articles

Competitive interactions affect perch-height preferences of three Odonata taxa (Coenagrionidae, Libellulidae)

Abstract Co-occurring odonate species often perch at different heights. We studied the effects of interspecific and intraspecific interactions on perch-height selection by Perithemis tenera, Pachydiplax longipennis, and Enallagma spp. by creating artificial perch stations and comparing perch selection when species perched alone or together. We also compared the frequency of perch-height use in the presence or absence of P. tenera and P. longipennis decoys (dead mounted specimens). When species perched alone, Enallagma spp. preferred low perches, P. tenera intermediate perches, and P. longipennis tall perches. This correlated with body mass; larger species used taller perches. Intraspecific responses to decoys were species specific; P. tenera showed an aggressive positive response to the presence of a conspecific decoy, whereas P. longipennis avoided conspecific decoys by shifting to lower perches. Interspecific effects were more consistent. The presence of living or decoy P. tenera at a station caused Ena...

PERCH CHARACTERISTICS OF ACADIAN FLYCATCHERS (EMPIDONAX VIRESCENS) IN SOUTHERN BOTTOMLAND HARDWOOD FORESTS

Perch-site selection is thought to be an important component of foraging success for sit-and-wait avian predators, such as flycatchers. Perch selection has further consequences for territorial advertisement and display. We quantified perch characteristics of Acadian Flycatchers in three bottomland hardwood forests in Arkansas, Louisiana, and South Carolina. We compared measurements made at flycatcher perches with those made at randomly selected trees and branches. In two of our study areas, flycatchers perched on dead limbs more often than expected by chance, and foliage volume was less around flycatcher perches than at randomly selected branches. Both of these results suggest a preference for foraging and displaying sites that provide a relatively unobstructed view. Discriminant function analysis revealed substantial overlap in perch-site characteristics among study areas, indicating that species-wide preferences were at least as important as local conditions in perch-site selection by Acadian Flycatchers.

Perch selection by singing chaffinches: a better view of surroundings and the risk of predation

Predation risk varies among perches, and the vulnerability of singing chaffinches (Fringilla coelebs) might differ depending on where they perch in a tree. To find out how singing of the chaffinch is associated with antipredatory behavior, I studied perch selection in mature pine forest and in pine saplings, two habitats differing in the amount of cover for protection from predators. My results show that male chaffinches prefer to sing below the canopy of mature pines and in the uppermost parts of sapling pines. Although these are the canopy parts most exposed to sparrowhawk (Accipiter nisus) attacks, staying in open sites may be a beneficial strategy for singing chaffinches because it makes it possible to improve antipredatory vigilance. This assumption was supported by the hawk experiments. After being exposed to the sparrowhawk model, all of the singing birds selected the conspicuous perch below the canopy of mature pines. The males that perched higher in the canopy before the experiment moved to the lower canopy, whereas those males that sang below the canopy did not change their singing perch.

Selection of habitat and perches by the Great Grey Shrike Lanius excubitor and the effects of snow layer and prey type

Field observations on Great Grey Shrikes Lanius excubitor were performed in four study areas in SW Finland (60°N, 22°E). The relation between habitat use, perch selection, prey type and the presence of a snow layer was evaluated. The mean yearly (± SE) territory size was 144 ha ± 14.3. The habitat selection depended on if snow cover was present, reflecting the favouring of vegetation-scarce arable fields when hunting invertebrates and vegetation-rich habitats when mainly vertebrates were available. Consistent with theories on optimal perch height, the shrikes chose higher perches when mainly vertebrates were hunted and also increased the time/perch, probably reflecting that vertebrate prey occur less frequently than invertebrate prey. The selection of lower perches when hunting invertebrates was evident in mild winter periods but not in the autumn; the reasons for this is discussed. The appearance of snow increased the distance to mammalian prey but the average capture frequency of mammals remained unchanged. In accordance with optimal foraging theory the shrikes preferred to hunt invertebrates when these were available rather than to adopt a hunting strategy that would optimise the encounter rate with vertebrates. However, the average hunting rate of ground-living prey decreased as the snow depth increased whereas energetically costly types of hunting behaviour, like rate of movements, hovering and hunting of birds remained unchanged.

BODY TEMPERATURE REGULATION IN A LATE-SEASON DRAGONFLY, SYMPETRUM VICINUM (ODONATA: LIBELLULIDAE)

Abstract Body temperature regulation and behavioral responses to temperature variation in the field were investigated in Sympetrum vicinum, a common North American libellulid that is most abundant as a mature adult in autumn. Because of its late flight season, this species is faced regularly with cooler environmental temperatures than most dragonflies investigated heretofore. By virtue of postural adjustments and perch selection, individuals are able to maintain both thoracic and head temperatures within a relatively narrow range even at ambient temperature as low as 10 °C. Physiological adaptations, including relatively low minimum temperature for effective flight and relatively rapid digestive function at low temperature, also enhance their ability to cope with cool conditions. Copulation and tandem oviposition and mate guarding interfere with the ability to regulate body temperature, although oviposition was observed at air temperature as low as 14 °C.

Factors Influencing the Selection of Basking Perches on Cardon Cacti by Spiny‐Tailed Iguanas (Ctenosaura hemilopha)1

ABSTRACTThe selection of optimal basking perches to achieve preferred body temperatures and avoid predation risks is one of the most important behavioral decisions that a lizard makes. We studied perch selection by the spiny‐tailed Iguana (Ctenosaura hemilopha) in Baja California Sur where they bask on elevated cacti. The more important factor determining cardon selection by iguanas was the presence of old woodpecker holes which could be used as refuges within the top 50 cm of a branch. Other factors are the height of the cardon, the presence of some other holes and the number of branches of the plant. These data suggest that predation risk is the strongest factor affecting the selection of certain cardons as basking structures by spiny‐tailed iguanas. Because the holes are mainly old woodpecker nests, the choice of a cardon as a refuge‐perching site has to be related to a prior selection by woodpeckers.

Male perch selection and the mating system of the robber fly,Promachus albifacies (Diptera: Asilidae)

We studied the activity and spatial distribution of the robber fly,Promachus albifacies, in a desert grassland habitat in central New Mexico. Late in the season males spent most of the daytime on or near cholla and yucca plants that had dead stems or dead flower stalks at least 1 m high. Of the three hypotheses (thermoregulation, foraging, mate encounter site) considered as explanations for this distribution, the mate-encounter-site hypothesis was best supported. Plants used by females as oviposition sites were the focus of male activity. Males perched within or near these plants and attempted copulations with females detected nearby. Most matings were initiated at these locations. Seasonal changes in male and female activity also supported the mate-encounter-site hypothesis. Early in the season, females spent little time ovipositing, and predictably, males spent little time on or near these plants. Such a mating system may be described as resource defense polygyny, since males acted aggressively toward one another at oviposition sites even when females were not present. However, the short tenure of males at these sites is suggestive of scramble competition polygyny. We discuss possible reasons why this particular mating system has evolved.

Responsiveness to conspecific and alien song by canaries (Serinus canaria) and European starlings (Sturnus vulgaris) as a function of photoperiod.

Nine canaries (Serinus canaria) and 8 European starlings (Sturnus vulgaris) were tested for responsiveness to conspecific song, alien song, or no sound at all. Responsiveness was assessed by letting the birds choose among perches associated with the different auditory stimuli. The birds were tested when they were adapted to short and to long photoperiods. The results showed that both species responded to song, especially conspecific song, more in the long-day condition than in the short-day one. For canaries, but not for starlings, perch selection also varied as a function of sex. These data show that responsiveness to song in songbirds changes as a function of day length

Perch Height Selection by Juvenile Sceloporus Lizards: Interspecific Differences and Relationship to Habitat Use

Perch height selection was studied in juvenile western fence lizards (Sceloporus occidentalis) and sagebrush lizards (Sceloporus graciosus) in the field and in the laboratory. In nature juvenile S. occidentalis were more arboreal than were juvenile S. graciosus. In laboratory experiments with lab-reared 3-4 wk old lizards, S. occidentalis perched off the ground more frequently. Differences between these two species in habitat preference are inferred to be at least partly innate, and emerge at an early age. Within each species, juveniles from different field populations differed in habitat use in the wild: lizards were more terrestrial at higher elevations. However, lab-reared juveniles from different populations of each species did not differ in laboratory tests of perch selection. In S. occidentalis there was evidence of individual variation in perch selection in the laboratory, but no among-family variation was detected.

Color Matching and Perch Selection by Lizards in Recently Burned Chaparral

The preference of Sceloporus occidentalis for perching on dark or light colored branches was studied in the field and in the laboratory. Lizards perched preferentially on dark branches and tended to avoid those which were light in color. In southern California chaparral active S. occidentalis perch selectively on blackened stalks of burned shrubs for at least several years following a fire. The lizards are cryptically colored on the black stalks and match reflectance within a few percent over the visible spectrum. However, as the char on the outer surfaces of the stalks wears off, the lizards are no longer color-matched, are seen less frequently on the stalks, and appear to center activities on rock outcrops. The association and color match between lizards and shrubs coincides with postfire conditions of reduced cover and increased predator abundance.