Perch Height Research Articles

Perch Height of the Arboreal LizardAnolis nebulosus(Sauria: Polychrotidae) from a Tropical Dry Forest of México: Effect of the Reproductive Season

We studied perch height in a population of the arboreal lizard Anolis nebulosus from Chamela, Jalisco, México. A total of 1697 lizards were captured during 1988 (June through December), 1989, 1990, and 1991 (June through July). Males used higher perches than females, particularly during the reproductive season. At the beginning of the reproductive season (March) males started to use higher perches, which were highest during the peak of reproductive activity. However, perch height use by females did not follow the same pattern. Females used high perches in March before beginning reproduction, lower perches during the reproductive season from June to August and higher perches again in October at the end of reproductive activity. These patterns suggest that reproductive activity is an important factor determining differential perch height use between sexes, with the priority for males being courtship displays and defense of their territory, whereas protection from predators is more important for females. Adults used significantly higher perches than juveniles and hatchlings, and overall perches were significantly higher during the wet than during the dry season. Perch height of females and males increased with body, environmental, and microenvironmental temperatures, suggesting that perch height might play an important role in thermoregulation.

THE LOCATION OF RANGING CUES IN WREN SONG: EVIDENCE FROM CALIBRATED INTERACTIVE PLAYBACK EXPERIMENTS

Abstract Many species of songbirds appear to monitor the distance to conspecifics by attending to songs received from them (ranging). Features of the habitat-induced degradation of the song seem to provide the ranging cues. This study investigates where, in a received, degraded song, the cues used for ranging lie; in the song elements, in the inter-element pauses or both. Examples of undegraded and degraded wren Troglodytes troglodytes song were cut into element and pause portions which were reassembled into four treatment types; two where the degradation between elements and pauses was concordant and two where either elements or pauses were degraded. These were played back at the boundaries of wren territories. The experiment was calibrated by measuring the degradation of the received playback songs and re-categorizing the trials into treatment types accordingly. Wrens responded to undegraded song by aggressively approaching and to degraded song with a less intense approach and an increase in perch height. When the level of degradation within the different song portions was concordant, subjects' responses were as expected from a wren ranging an intruder (undegraded) or a distant conspecific (degraded). When only the pauses were derived from a degraded song the behaviour closely resembled a wren ranging a distant rival, however the signal with only degraded elements elicited a response of intermediate intensity. We conclude that wrens seem able to adjust their response relative to degradation cues in either the elements or the pauses of degraded songs. In addition, the pause degradation seems to offer cues that can be used independently of element degradation, whereas element degradation needs the congruity of cues within the pauses to evoke a response equivalent to that elicited by the degraded song.

Behavioral Ontogeny in Free-Ranging Juvenile Male and Female Green Anoles, Anolis carolinensis, in Relation to Sexual Selection

Anolis carolinensis is sexually dimorphic in behavior and morphology in adults, primarily due to intrasexual selection acting to produce large, conspicuous, and aggressive males. However, the extent to which selection pressures acting on adults might also produce sex differences during ontogeny, but before sexual maturity, has not been considered. During June-August 1995 and 1996, I recorded the behavior of 20 juvenile male and 17 juvenile female A. carolinensis for 30-60 min each at a field site near Augusta, Georgia, USA: (1) to determine if as groups, juvenile males and females behaviorally differ, thereby suggesting the presence of sex differences from hatching; and (2) to determine if juvenile males or females show sex- specific, size-related behavioral changes, in order to describe the ontogenetic schedule by which sex differ- ences in behavior arise. I examined potential indicators of sex differences in space use (perch height and diameter, home range volume), social behavior patterns (body color and shift rate, nearest neighbor distance, headbobbing display rate, and display context), and behavior patterns affecting growth (feeding rate and foraging mode, proportion of time spent moving). Based on potential tradeoffs between behavior relevant to the immediate life history of juveniles and behavior that will lead to future reproductive success, I hypothesized that juveniles would show no sex differences in space use or social behavior patterns, but would differ in behavior patterns affecting growth. As expected, juvenile males ate and foraged actively more often than juvenile females. Furthermore, overall comparisons between juvenile males and females revealed no sex differences in space use or social interaction. However, contrary to my hypotheses, juvenile males did not decrease amounts of time spent moving with respect to juvenile females, and larger males occupied larger home ranges and spent more time green while females showed no ontogenetic shifts in these variables. My results suggest that juvenile A. carolinensis show both sex differences present from hatching and arising through ontogeny leading up to the adult endpoints, and that these differences may arise through the effects of sexual selection on ontogeny.

THE RELATIONSHIP BETWEEN SEXUAL SIZE DIMORPHISM AND HABITAT USE IN GREATER ANTILLEANANOLISLIZARDS

Sexual size dimorphism (SSD) is the evolutionary result of selection operating differently on the body sizes of males and females. Anolis lizard species of the Greater Antilles have been classified into ecomorph classes, largely on the basis of their structural habitat (perch height and diameter). We show that the major ecomorph classes differ in degree of SSD. At least two SSD classes are supported: high SSD (trunk-crown, trunk-ground) and low SSD (trunk, crown-giant, grass-bush, twig). Differences cannot be attributed to an allometric increase of SSD with body size or to a phylogenetic effect. A third explanation, that selective pressures on male and/or female body size vary among habitat types, is examined by evaluating expectations from the major relevant kinds of selective pressures. Although no one kind of selective pressure produces expectations consistent with all of the information, competition with respect to structural habitat and sexual selection pressures are more likely possibilities than competition with respect to prey size or optimal feeding pressures. The existence of habitat-specific sexual dimorphism suggests that adaptation of Anolis species to their environment is more complex than previously appreciated.

THE RELATIONSHIP BETWEEN SEXUAL SIZE DIMORPHISM AND HABITAT USE IN GREATER ANTILLEAN ANOLIS LIZARDS

Sexual size dimorphism (SSD) is the evolutionary result of selection operating differently on the body sizes of males and females. Anolis lizard species of the Greater Antilles have been classified into ecomorph classes, largely on the basis of their structural habitat (perch height and diameter). We show that the major ecomorph classes differ in degree of SSD. At least two SSD classes are supported: high SSD (trunk-crown, trunk-ground) and low SSD (trunk, crown-giant, grass-bush, twig). Differences cannot be attributed to an allometric increase of SSD with body size or to a phylogenetic effect. A third explanation, that selective pressures on male and/or female body size vary among habitat types, is examined by evaluating expectations from the major relevant kinds of selective pressures. Although no one kind of selective pressure produces expectations consistent with all of the information, competition with respect to structural habitat and sexual selection pressures are more likely possibilities than competition with respect to prey size or optimal feeding pressures. The existence of habitat-specific sexual dimorphism suggests that adaptation of Anolis species to their environment is more complex than previously appreciated.

Parental investment, potential reproductive rates, and mating system in the strawberry dart-poison frog, Dendrobates pumilio

We studied the effect of relative parental investment on potential reproductive rates (PRRs) to explain sex differences in selectivity and competition in the dart-poison frog Dendrobates pumilio. We recorded the reproductive behavior of this species in a Costa Rican lowland rainforest for almost 6 months. Females spent more time on parental care than males, and `time out' estimates suggest that PRRs of males are much higher than than those of females, rendering females the limiting sex in the mating process. Males defended territories that provide suitable calling sites, space for courtship and oviposition, and prevent interference by competitors. Male mating success was highly variable, from 0 to 12 matings, and was significantly correlated with calling activity and average perch height, but was independent of body size and weight. Estimates of opportunity for sexual selection and variation in male mating success are given. The mating system is polygamous: males and females mated several times with different mates. Females were more selective than males and may sample males between matings. The discrepancy in PRRs between the sexes due to differences in parental investment and the prolonged breeding season is sufficient to explain the observed mating pattern i.e., selective females, high variance in male mating success, and the considerable opportunity for sexual selection.

Notes on the natural history and habitat use of Eleutherodactylus fitzingeri (Anura: Leptodactylidae)

AbstractEleutherodactylus fitzingeri were studied during the dry and rainy seasons at an Atlantic lowland rainforest in Costa Rica. The frogs had one of three dorsal colour patterns (mottled, striped, uniform) and one of two ventral colour patterns (white, yellow). Males had significantly more often a yellow venter than females. Juveniles with a white belly were significantly smaller than juveniles with a yellow belly. Males perched higher than females and juveniles. Perch height in males did not vary with the time of day, weather conditions or behaviour. Calling males used more sheltered perches than silent males, and males calling by day used more sheltered perches than males calling by night. Reproductive activity increased greatly at the onset of the rainy season. Males showed little site attachment.

The effect of foraging material and perch height on feather pecking and feather damage in laying hens

Feather pecking in laying hens ( Gallus gallus domesticus) may not only cause welfare problems, but also result in economic losses due to feather damage and increased mortality. The present study aimed at testing whether foraging material and perch height have significant effects on feather pecking and feather damage. From week 19 to week 30 after hatching, groups of 14 hens (white `Lohman Selected Leghorn' hybrids) were kept in pens with or without access to polystyrene blocks as foraging material and with low or high perches (45 cm or 70 cm above floor level; 2×2 factorial design; four pens each per housing condition). Time since introduction of the hens into the experimental pens ( P<0.0001) and provision of foraging material ( P<0.002), but not perch height, had significant effects on the rate of feather pecking interactions. Feather pecking was less frequent in pens with than without polystyrene blocks. On the other hand, feather damage in week 30 was significantly more pronounced in pens with low than with high perches ( P<0.05), but not significantly influenced by the provision of foraging material. Hens sitting or standing on the floor were especially likely to elicit feather pecking. Individuals characterised by relatively high rates of feather pecking showed more severe forms of this behaviour. It is concluded that hens should be provided with foraging material and high perches during the laying period to reduce feather pecking and feather damage.

Spatial and Breeding Relationships of the Lizard, Anolis Carolinensis: Evidence of Intrasexual Selection

1. We used continuous 8-day monitoring to document the spatial and mating relationships of free-ranging Anolis carolinensis lizards at each of seven habitat-delineated study sites. 2. We found a polygynous social structure, consisting of a male and 2-6 resident females (x = 3.3), on each site. 3. Spatially, both sexes utilized all available perch heights and diameters on the study sites (habitat generalists), though females tended to perch slightly higher and on significantly thinner substrata (x = 2.4 m, 3.4 em, respectively) than males (x = 2.3 m, 5.3 em, respectively). 4. Mean home range volume was eight fold greater for males (69 m3) than females (8 m3). Male home ranges were exclusive of other males (0% overlap), while neighboring female home range volumes overlapped an average of 18%. 5. Male snout-vent length (SVL) was positively correlated with male home range size (area, volume) and with number of resident females, but not with resident female SVL or resident female home range size. 6. Half of 397 male-female encounters led to close contacts in which males influenced courtship outcomes by: recognizing receptive and non-receptive females (differential display rate); bypassing 69% (85/123) of mating opportunities with receptive females; and copulating only when courtship was male-initiated. 7. Larger males (who also had larger territories and more females) courted less per female, but with longer duration, and had longer copulatory durations than smaller males. 8. Male frequency of copulation (x = once/1.4 days), however, had no correlates with measured variables; females were mated without bias to male or female attributes. 9. Male potential reproductive rate (PRR), estimated from the number of copulations with different females, positively correlated with male SVL. Female PRR, estimated from the inter-mating interval (i.e. the single-egg clutch interval), did not correlate with any measured male or female trait. 10. Our data, in concert with other field studies and A. carolinensis life history traits, document a polygynous mating system in which females seem to fit a 'no cost, neutral-mate-choice' model, and males (in response to sedentary, contiguously distributed females who clutch at weekly intervals over a 4-month period) employ territorial contests within an endurance rivalry as a prime mechanism for mate assortment.

A COMPARISON OF EVOLUTIONARY RADIATIONS IN MAINLAND AND CARIBBEANANOLISLIZARDS

Comparisons between closely related radiations in different environments provide a unique window into understanding how abiotic and biotic factors shape evolu- tionary pathways. Anolis lizards have radiated extensively in the West Indies, as well as mainland Central and South America. In the Caribbean, similar communities of anole species specialized for different habitats (ecomorphs) have evolved independently on each Greater Antillean island. We examined ecological and morphological data on 49 Anolis species (33 Caribbean, 16 mainland) to investigate whether the same set of ecomorphs has arisen in mainland regions. More generally, we investigated whether the relationship between ecology and morphology was similar among anoles in the two regions. Radiations in the two regions are very different. The majority of mainland anole species exhibit morphological characteristics unlike any Caribbean ecomorph. Furthermore, rela- tionships between ecology and morphology are very different between the two sets of anole species. Among mainland anole species, toepad size is positively correlated with perch height, whereas tail length is negatively related to perch diameter. In contrast, among Caribbean anole species, both forelimb length and body mass are positively associated with perch diameter, and both tail length and hindlimb length are negatively related to perch diameter. Biomechanical considerations provide a functional basis for some of these cor- relations, but much variation remains to be explained. These findings demonstrate that factors that caused anole species to converge repeatedly in the West Indies are not present in mainland regions, and that environmental factors can strongly influence the shape of evolutionary radiations.

Microhabitat Analysis of three Fen-grassland Grasshopper species (Acrididae: Gomphocerinae)

Based on an individual data recording of 13 biotic and abiotic microhabitat variables, the microhabitat of 3 sympatric and coexisting fen-grassland grasshoppers was analyzed. The investigated species were closely related Chorthippus albomarginatus Degeer 1773, Chorthippus montanus Charpentier 1825, and Chorthippus parallelus Zetterstedt 1821 (Acrididae: Gomphocerinae). The application of Principal Components Analysis combined 70.4% of the recorded data to 3 main factors: (a) Perch height in the vegetation and its density, (b) leaf canopy, and (c) microclimate, describing the microhabitat of the 3 species in a sufficient way. Supported by 3 ecological standard calculations, the results show a finely tuned microhabitat utilization, confirming a strategy of competition avoidance of the 3 species in case of coexistence. Even on microhabitat scale Ch montanus is stenoecious, whereas Ch albomarginatus and Ch parallelus are euryecious. Thus, the species' macrohabitat requirements are continued in the microhabitat.

Ecological Variation among Populations of the Gekkonid Lizard Gonatodes humeralis in the Amazon Basin

Comparisons of ecological and reproductive data among three well-studied and two lesser-studied populations of Gonatodes humeralis in the Amazon region revealed geographic variation in adult snout-vent length, morphology, habitat distribution, perch height, and prey types. Populations were similar in size of prey, and there was no correlation of lizard body size with prey size. A population of G. humeralis in the western Amazon (Ecuador) occurred only on human-made structures and was not found in undisturbed forest. Populations in the Brazilian Amazon occurred primarily in undisturbed forest. Apparent habitat shift in Ecuador suggests that the population studied was introduced by humans. Geographical variation in ecological traits suggests the value of repeated studies in different parts of species' ranges.

Perch availability and ground cover: factors that may constitute suitable hunting conditions for pale chanting goshawk families

We investigated the impact ot perch height and abundance, and the cover lor prey, on the hunting tactics of perch-hunting pale chanting goshawks (Melierax canorus). Although pale chanting goshawks demonstrate a clear preference lor perching on the highest available perches, the availability of perches is of more importance than height because these birds hunt almost exclusively from perches, move regularly between them, and an increased number of perches increases the area of habitat accessible for elfective hunting. In Succulent Karoo, pale chanting goshawks occupied areas where perch density (16 natural and 122 artificial/25 ha) was significantly higher than in unoccupied areas (8 natural and 12 artificial/25 ha). The high proportion of cover formed by natural perches (trees and shrubs; 36%) and the low proportion of open ground (42%) resulted in Closed Spekboomveld being unsuitable lor pale chanting goshawks, relative to the adjacent Open Spekboomveld that supported goshawks by offering a less restrict...

Prey selection by sparrowhawks,Accipiter nisus: relative predation risk for breeding passerine birds in relation to their size, ecology and behaviour

Predation is a fundamental ecological process, but there are few studies of predation risk for adult, breeding birds. In this study, we quantified Relative Predation Risk (RPR) for 46 species of passerine birds preyed on by sparrowhawks during the breeding season in south-western Sweden. The sparrowhawk is a major predator of smaller birds in Eurasian forests and woodland. Near nesting hawk pairs, prey abundance was estimated by line transects. From prey remains at hawk nests, we estimated the frequency of prey species in the diet of hawks. For each hawk pair, RPR values for different prey species were calculated. The mean RPR for each prey species, based on hawk pairs as sample units, indicated degree of overrepresentation (positive RPR) or underrepresentation (negative RPR) of the prey in the diet. Prey species with a high positive RPR nested mainly near human habitations (villages or towns), at forest edges and in farmland. However, there were marked seasonal changes in RPR. Forest birds, such as the goldcrest and wren, had the highest RPR in April. Later, the hawks seemed to hunt mainly in the habitats mentioned above, where prey were more abundant or easier to catch, resulting in increasing RPR for the house sparrow, yellowhammer, greenfinch and other species. RPR values were analysed in relation to prey body size (mass) and relative density, as well as prey foraging height and nest height (categorized from the literature). In addition, the mean perch height and mean exposure of prey species were quantified in the field. Most predation was due to the smaller male hawks, providing food for their mates and young, RPR increased with prey body size up to a mass of about 40 g, then declined with increasing body size (larger prey being more difficult to catch), RPR decreased with increasing relative density of prey species. Nest height was not correlated with RPR, but foraging height seems to be an important factor: RPR decreased with increasing foraging height. A similar result was found for mean perch height, when larger prey (over 40 g) and singing individuals were excluded from the field data. RPR increased with mean exposure of prey species when larger prey and singing birds were excluded; a combination of perch height and exposure improved the correlation with RPR. Singing birds were generally perched high in the vegetation and may not suffer high predation risk, contrary to common belief. The results of this study are discussed in relation to temporal and geographical variation in RPR and antipredator adaptations in passerine birds.

Responses of Bald Eagles to Human Activity During the Summer in Interior Alaska

Along narrow rivers, spatial restriction of human use based on wildlife responses can effectively eliminate the entire river corridor from human use. Therefore, if river use by both wildlife and humans is a goal, an alternative management strategy is necessary. We measured flush response rate and flush distance of breeding and nonbreeding Bald Eagles (Haliaeetus leucocephalus) to recreational boating along the Gulkana River in interior Alaska from 1989 to 1992. Eagle responses to our nonmotorized boat were governed by the context within which human‐eagle encounters occurred. Flush response rate of nonbreeding eagles decreased as perch height and its distance from the river's edge increased, increased as the season progressed and as eagle group size increased, was lower for juveniles (20%) than other age classes (49‐65%), and varied with the existing level of human activity in a geographic location (P &lt; 0.01 for all parameters). Flush distance of nonbreeding eagles increased as the distance a disturbance was first visible to a perched eagle increased, as perch height and its distance from the river's edge increased, and as the season progressed. In contrast to flush response, flush distance was strongly associated with age and was greatest for adults, least for juveniles, and intermediate for subadults. Breeding adults were much less likely to flush than nonbreeding adults, and flushed at lesser distances. We recommended that along narrow wilderness rivers, the impacts of human activity on Bald Eagle populations be regulated with temporal, rather than spatial, restrictions.

Behavioral Interference for Perch Sites in Two Species of Introduced House Geckos

Behavioral Interference for Perch Sites in Two Species of Introduced House Geckos

Preliminary checklist and field observations of the butterflies of the Maquipucuna Field Station (Pichincha Province, Ecuador)

The Maquipucuna Tropical Reserve (MTR) contains one of the few remaining fragments of rainforest in western Ecuador. A survey of butterfly species richness was performed by walking an altitudinal transect (1270 to 1900m) through MTR forest habitats from late August to Octo- ber, 1989, and late November to early December, 1992. In 350 collector hours, 220 butterfly species were observed; some are characteristic of lowland tropical forests, others of Andean cloud forests and bamboo thickets. Habitat affinities, altitudinal distributions, feeding and perching behaviors were noted and discussed for many species. Cylindrical net traps baited with rotting fruit were used to collect 21 butterfly species, mostly charaxine and satyrine nymphalids. We observed apparent zonation by elevation or habitat among three species of Taygetis (Satyrinae) and vertical zonation in perch height among three species of Adelpha (Liminitinae). Future surveys performed from January to July and extend- ing to the southern limits of the MTR (above 1900m) should identify many more butterfly species.

The calling behaviour and spatial distribution of male bushcrickets (Sciarasaga quadrata) and their relationship to parasitism by acoustically orienting tachinid flies

Abstract. This paper examines the calling behaviour and spatial distribution of male Sciarasaga quadrata Rentz (Orthoptera: Tettigoniidae), a bushcricket that is subject to attack by an acoustically orienting parasitoid fly, Homotrixa sp. (Diptera: Tachinidae: Ormiini). Checks on calling activity in populations of S.quadrata confirmed that calling began 2–3 h before sunset and continued well beyond midnight. Calling activity was not restricted by temperature with males calling over air temperatures of 10.6–24.2°C. Nearest‐neighbour analyses, within the sampled areas, revealed that the spacing between calling males was random and the minimum distance between calling males was 3.74 m. Mean distances between calling males varied between 9.2 m and 23.0 m and significantly changed as male density, which peaked at 0.36 calling males per 100 m2, declined over the calling season. Males showed no preference for any one plant species, with their distribution across bushes not significantly different to the frequency of the plants within the habitat. The perch height of calling males was on average half way up the height of a bush and was significantly influenced by the height of the bush. Perch height was not significantly influenced by proximity to calling males or by whether or not males were parasitized. Site fidelity of males was low with only 0–10% of bushes occupied by calling males over successive nights. Males, though flightless, moved on average 6.70 m and up to 26.56 m per night. No evidence was found for the use of aggregation in S.quadrata as a primary defence against ormiine attack. Commencing calling prior to sunset, frequent movement, and a lack of association with any particular plant species, although possibly relevant to ormiine attack, could also be explained in terms of other activities such as male‐male interactions and mating behaviour.

Habitat use and activity patterns of roach (Rutilus rutilus (L.)), rudd (Scardinius erythrophthalmus (L.)), perch (Perca fluviatilis L.) and pike (Esox lucius L.) in the laboratory: the role of predation threat and structural complexity

Abstract– The role of predation risk and structural complexity in determining the habitat use and activity patterns of roach, rudd and perch was assessed using a series of video‐recorded laboratory trials. The time spent in open and structured habitats, vertical swimming heights and activity levels of each species were observed in the presence and absence of a potential, pike, predator. Habitat complexity varied between treatments with artificial stem densities of 200, 400 and 600 stems‘m−2. Predator free trials showed that roach and rudd spent significantly less time in structured habitats than perch. Increasing stem density had no significant effect on the habitat choice of perch but did affect the distribution of roach and rudd. Stem density influenced the vertical swimming height of rudd or perch but not roach, although the effects of habitat complexity on swimming activity were more complicated. Pike were themselves influenced by increases in stem density, only selecting structured habitats when stem densities were less than 600 stems‘m−2. In the presence of a predator, both roach and rudd increased the amount of time spent in structured areas. These observed differences were independent of stem density. Perch, however, decreased the amount of time spent in structural habitats at all stem densities. Predation risk also prompted significant changes in both vertical swimming height and activity levels of potential prey fish. A pike predation success hierarchy of rudd‐roach‐perch was also observed during the study. The reasons for this pattern are discussed.

Factors affecting the flight distance of the Dusky Thrush Turdus naumanni

Flight distances were measured in the Dusky Thrush, Turdus naumanni, in winter. Predictive models relating flight distance of the thrush to environmental variables were developed and tested using stepwise multiple regression. The models, based on analyses of possible independent variables collected in 1984 and 1985, accounted for 54% and 82% of the variation in flight distance, respectively. The most important independent variables were location of the thrush (whether it was within 10 meters from the nearest shelter belt or not) and snow depth in 1984, and distances from the thrush to the nearest shelter belt and perch height in 1985. Longer flight distances were recorded further away from shelter belt. Snow fall made the flight distance shorter. Based on the multiple regression model in 1985, I predicted flight distance of thrushes and the time until they flew off for each distance from the shelter belt and showed that a thrush would stay a longer time before it flew off near shelter belts.