Preference For Open Habitats Research Articles

Ontogenetic behavior and migration of kaluga, Huso dauricus

We conducted laboratory experiments with early life stages of kaluga sturgeon, Huso dauricus, from the middle reach of the Amur River to quantify ontogenetic behavior and compare their behavior with similar laboratory data collected previously on young kaluga from the Amur River. Our hatchling free embryos initiated an intense downstream migration that peaked on day 1, and continued strongly to day 3, decreased strikingly during days 4–6, and ceased on day 7 (8-day migration). Migrants preferred a bright habitat (illuminated and white bottom), open habitat, and swam-up far above the bottom (daily median distance, 3.5 m). On days 21–22, larvae initiated a second downstream migration of similar intensity (four fish passes per 5 min), with a peak at 34–35 days. Juveniles continued a slow intensity migration (one fish pass per 5 min) until day 66, indicating a long-duration migration style by early life stages that would carry them far downstream from a spawning site. Free embryos, larvae and early-juveniles also strongly preferred open habitat, suggesting a similar use of this habitat type by wild individuals of these three life stages. The behavior and migration of our kaluga early life stages were similar to the young kaluga studied previously, but the migration of the two groups was different in major ways. This result suggests there are at least two breeding stocks in the river, each with a slightly different early behavior. If correct, culture programs for stock enhancement must ensure breeding populations are not mixed, which would produce non-adapted early life stages. Genetics studies are needed to identify the kaluga populations in the Amur River.

Movements of European bison (Bison bonasus) beyond the Białowieża Forest (NE Poland): range expansion or partial migrations?

The European bison is the largest terrestrial mammal in Europe. After extinction in the wild at the beginning of the twentieth century, it was re-introduced to Białowieża Forest and other woodlands in Eastern Europe. In this paper, we analysed the movements of European bison beyond the continuous woodlands of the Białowieża Forest (NE Poland) between 1964 and 2010. In total, 1,117 direct observations of bison were collected. The number of males moving out of the forest fluctuated during the study period, whilst the number of females steadily increased. The number of male observations outside of the forest per annum was dependent on the population size and snow depth, whilst the number of cows in mixed groups moving outside of the forest was correlated with the population size only. Males were observed mainly alone (50 % of observations) or in small groups of two to three individuals (25 %); however, distribution of group size differed from those observed in the population. There was a significant difference between the direction of movement of males and females out of the forest—males moved mainly west and southwest, whilst females moved to the north. This was also significantly different from the expected movement direction. The mean distance of bison observations from the forest border was 1.8 ± 0.13 km and did not differ significantly between sexes. After 1990, males were observed significantly farther away from the forest (2.2 km) than in the previous years (0.9 km). Most observations (94 % of bulls and 93 % of cows) were up to 5 km from the forest edge. The range of bison in the vicinity of the Białowieża Forest was strictly seasonal. Most observations (78 % in males and 88 % in females) were recorded from November to April. Increasing utilisation of areas beyond the forest habitats may be driven by different factors but most probably it is related to range expansion and the bison's preference for open habitats. The strong seasonal pattern of bison movements indicate that the partial seasonal migrations were initiated in the Białowieża population.Electronic supplementary materialThe online version of this article (doi:10.1007/s13364-013-0136-y) contains supplementary material, which is available to authorized users.

On their knees: distal femur asymmetry in ungulates and its relationship to body size and locomotion

ABSTRACT Asymmetry of the knee (distal femur), where the medial trochlear ridge is larger than the lateral one, has been observed in certain ungulates, but until now there has not been a comprehensive study of this anatomy across a range of extant and extinct mammals. A degree of knee asymmetry is present in most ungulates: this asymmetry increases in extent with increasing body size, and is also more prominent in taxa with a preference for open habitats, independent of body size. However, camelids and proboscideans have symmetrical knees, regardless of size. We propose that the correlation of degree asymmetry with habitat type, as can be observed in extant ruminants, is related to the preferred type of locomotion, with the gallop gait being preferred in open habitats. Neither camelids nor proboscideans employ the gallop as a habitual gait. The allometric increase observed in knee asymmetry, in combination with the correlation with locomotor preference, likely reflects anatomy that resists muscular forces pulling the patella medially when the animal is supporting its weight on a single hind leg during fast locomotion. Inclusion of fossil taxa leads to interesting interpretations about the behavior of extinct ungulates: extinct brachydont equids of presumed closed habitat preference have less asymmetric knees than extant equids, or extinct hypsdont equids of presumed open habitat preference; the knee anatomy of giant deer, Megaloceros, indicates a preference for open habitats, whereas the knee anatomy of the brontothere Megacerops indicates a proboscidean (versus rhino-like) type of fast locomotion.

Vulnerability of small and medium-sized prey mammals in relation to their habitat preferences, age classes and locomotion types in the temperate Monte Desert, Argentina

In this study we examined predation by small felids upon small and medium-sized prey mammals in the central region of the Monte Desert. We analyzed the degree of vulnerability of prey mammals in relation to their habitat use patterns, modes of locomotion and age classes. Medium and small rodents were the predominant prey in the diet of small cats. The most consumed small mammal was Akodon molinae, which inhabits areas of dense cover, while species occurring in open habitats such as Eligmodontia typus were less consumed. Among medium-sized mammals, Galea leucoblephara that depends on patches with high plant cover for refuge was more consumed than Microcavia australis that lives in colonies and displays a complex set of antipredator strategies. Prey selectivity on small rodents showed that E. typus, which uses bipedal locomotion and an erratic escape behaviour, was consumed in greater proportion than its availability. We suggest that although its specialized locomotory mode would diminish predator attacks, its preference for open habitats would increase the probability of predator–prey encounter. Consumption of small mammals focuses mostly on adult individuals. However, we found a significant consumption of senile individuals of A. molinae, which points out that vulnerability tends to be high towards the age of maturity in this species.

Holocene survival of the wild horse in Europe: a matter of open landscape?

AbstractThe wild horse Equus ferus was one of the most frequent species of the Late Pleistocene large ungulate fauna in Eurasia and played an important role in the subsistence of human groups, especially at the end the Late Glacial. It is frequently assumed that E. ferus became extinct in Europe at the beginning of the Holocene because of the development of woodlands and loss of open habitats. Because of its preference for open habitats and in spite of its adaptability, the appearance or disappearance of the wild horse could therefore be a suitable palaeoecological indicator for the opening of the Holocene primeval woodlands. We revised the dating and reliability of the subfossil record and dated several bones by atomic mass spectrometry 14C dating. From the beginning of the Holocene (9600 cal a BC) to the end of the Atlantic Period (3750 cal a BC) there are 207 archaeological sites with wild horse records available in Europe. E. ferus survived the Pleistocene Holocene transition in Europe, but the spatiotemporal dynamics of populations fluctuated remarkably in the early and middle Holocene. Small and sparse populations increasingly became extinct during the early Holocene, until between 7100 and 5500 cal a BC the wild horse was almost absent in central parts of the European Lowlands. Particular conditions in natural open patches in the canopy forests, chalklands and floodplains may have maintained the local survival of the horse in some regions of the Lowlands, however. In the Late Atlantic, between 5500 and 3750 cal a BC the range of the wild horse was again extended. It re‐immigrated into central and western Europe, probably as a consequence of increasing landscape opening by Neolithic peoples. The data presented here may be a valuable part of the debate on the degree of openness of the early and middle Holocene landscape. Copyright © 2011 John Wiley & Sons, Ltd.

Resources driving landscape-scale distribution patterns of grazers in an African savanna

In order to effectively manage and conserve indigenous herbivores, a good understanding is needed of how resources drive their distribution patterns. This study employed a unique dataset to test a range of ecological theories and hypotheses on free-ranging grazers. Using aerial census data collected over 14 yr across the 2 million ha Kruger National Park (South Africa), this study employs spatial autologistic regression models to explore the spatial relationships that exist between the distribution of eight indigenous grazer species and a set of resource variables. It was found that ecological theories relating to feeding guild, water-dependence, allometric scaling, gut-morphology and vulnerability to predation could explain most of the grazer distribution patterns observed in relation to surface-water, forage quality, forage quantity and habitat openness. All the grazers studied were water-dependent and occurred close to a permanent source of water in the dry season. This was ascribed to the lack of moisture in the diet of grazers during the dry season. Most ruminants' distribution patterns were significantly associated with areas of high forage quality whereas hind-gut fermentors were neutral towards forage quality. Average forage quantity was not a significant predictor of long-term, landscape-scale distribution patterns for any of the grazer species studied. Most small- and medium-bodied grazers preferred open habitats above closed habitats, probably due to higher visibility and a lower predation risk. Large-bodied grazers did not bias their distribution patterns towards open habitats. The way in which grazers distribute themselves with respect to different resources can potentially inform management actions on appropriate scales.

Habitat Selection of a Large Herbivore at High Density and Without Predation: Trade-off between Forage and Cover?

selection under harsh environmental conditions. We fitted 19 female white-tailed deer with global positioning system collars and delineated summer home ranges and core areas. We sampled vegetation in the core areas and in the rest of the home ranges to determine abundance of forage and forest cover within habitat patches, and assessed habitat selection between open and forested habitat patches. At a coarse scale, white-tailed deer preferred open habitat patches over forested ones, suggesting that they adopted a foraging strategy favoring energy intake. At a fine scale, habitat selection was influenced positively by the percentage of ground cover of forbs and deciduous shrubs, but negatively by conifer density. The biomass of preferred plant species, lateral cover, fir regeneration, and distance to the nearest open–forest edge were not strong predictors of habitat selection by deer. We conclude that fine-scale habitat selection by white-tailed deer at high population density and in the absence of predation is mainly determined by forage abundance. These patterns of habitat selection demonstrate that herbivores can adjust their behavior to other limiting factors when predation risk is relaxed.

Habitat requirements of weasels Mustela nivalis constrain their impact on prey populations in complex ecosystems of the temperate zone

Differences in habitat use by prey and predator may lead to a shift of occupied niches and affect dynamics of their populations. The weasel Mustela nivalis specializes in hunting rodents, therefore habitat preferences of this predator may have important consequences for the population dynamics of its prey. We investigated habitat selection by weasels in the Białowieza Forest in different seasons at the landscape and local scales, and evaluated possible consequences for the population dynamics of their prey. At the landscape scale, weasels preferred open habitats (both dry and wet) and avoided forest. In open areas they selected habitats with higher prey abundance, except during the low-density phase of the vole cycle, when the distribution of these predators was more uniform. Also in winter, the distribution of weasels at the landscape scale was proportional to available resources. In summer, within open dry and wet habitats, weasels preferred areas characterised by dense vegetation, but avoided poor plant cover. In winter, weasels used wet open areas proportionally to availability of habitats when hunting, but in contrast to summer, they rested only in habitats characterized by a lower water level, which offered better thermal conditions. At the local scale, the abundance of voles was a less important factor affecting the distribution of these predators. Although we were not able to provide direct evidence for the existence of refuges for voles, our results show that they may be located within habitat patches, where availability of dense plant cover and physiological constraints limit the activity of weasels. Our results indicate that in complex ecosystems of the temperate zone, characterized by a mosaic pattern of vegetation types and habitat specific dynamics of rodents, impact of weasels on prey populations might be limited.

Nesting biology of Centris (Hemisiella) tarsata Smith in southern Brazil (Hymenoptera, Apidae, Centridini)

A total of 67 nests of Centris tarsata were obtained from wood trap-nests of different diameters, consisting of a linear series of brood cells built with sand mixed with oil. This species showed a preference for open habitats, since it occurred only in Swamp and Grassland areas and has never been found in the Araucaria forest. Nesting activity was bigger during the hot season, especially in December and January. The Sex ratio was of 1.48:1 (females/males), significantly different from 1:1. The females were larger than the males and these showed no dimorphism. Males were produced in the outermost cells and females in the innermost cells. C. tarsata presented a direct development without diapause in larval stage. They overwinter as adults. Development time was similar for males and females. Natural enemies are Bombyliidae Mesocheira bicolor, Coelioxys sp. and Meloidae.

The spatial ecology of the Rosy-faced Lovebird Agapornis roseicollis in Namibia

Eight Rosy-faced Lovebirds from two study sites and four colonies in Namibia's Claratal and Hohewarte districts were tagged and their local movements tracked using radio transmitters. The birds' movements averaged 415.7 ± 391.3m in summer and 1 030.5 ± 1 068.6m in winter. There were marked seasonal differences in flight distances to feeding grounds, suggesting food resource scarcity in winter. The lovebirds preferred open grassland habitat with scattered shrubs where the most preferred diet, the seeds of Anthephora schinzii, was abundant. Home range areas varied, but averaged 0.59 ± 0.52km2 and overlapped greatly. The birds were crepuscular and highly social, with a mean flock size of 7.3. The birds' movements averaged 415 ± 3.3m in summer and 1 030 ± 1 068m in winter.

Evaluating the Predicted Local Extinction of a Once‐Common Mouse

Abstract: In an earlier paper (Pergams & Nyberg 2001) we found that the proportion of the prairie deer mouse (Peromyscus maniculatus bairdii), among all local Peromyscus museum specimens collected in the Chicago region, had significantly declined over time. This proportion changed from about 50% before 1900 to <10% in the last 25 years. Based on this proportion a regression model predicted the local extinction of the prairie deer mouse in 2009. To evaluate that prediction, we estimated current deer mouse abundance by live trapping small mammals at 15 preserves in Cook and Lake counties, Illinois (USA) at which prairie deer mice had previously been caught or that still contained their preferred open habitat. In 1900 trap nights, 477 mammals were caught, including 251 white‐footed mice (P. leucopus), but only one prairie deer mouse. The observed proportion of Peromyscus that were prairie deer mice, 0.4%, was even lower than the 4.5% predicted for 2000. Here we also introduce a simple, new community proportions model, which for any given geographic region compares the proportions of species recently caught with the proportions of species in museums. We compared proportions of seven species collected in Cook and Lake counties and examined by Hoffmeister (1989) with proportions of these species that we caught. Ten percent of the museum community was prairie deer mice, but only 0.2% of our catch was. The current local scarcity of the prairie deer mouse is consistent with the regression‐based prediction of its eminent local extinction. More conservation attention should be paid to changes in relative abundance of once‐common species.

Habitat use by Oncifelis guigna and Pseudalopex culpaeus in a fragmented forest landscape in central Chile

Native forests in Chile have been replaced by exotic plantations, generating a mosaic of forest fragments immersed in a matrix of plantations and farms. This landscape change could affect habitat availability for native carnivores such as Oncifelis guigna (Felidae) and Pseudalopex culpaeus (Canidae). We determine the potential impact of native forest fragmentation on these species, assessinghabitat use by these carnivores. The study was carried out in continuous forest (150 ha), native forest fragments (<10 ha) and surrounding pine plantations in central Chile (35°59′ S, 72°41′ W). We placed scent-stations (SSs) in three types of habitat from January to August 2000, setting a total of 620 SSs to determine habitat selection. We characterized structure and composition of 100 m2 of vegetation aroundevery SS, and measured its distance to nearest native forest patch, road and bottom creek. O. guigna preferred habitats with dense bush cover, far from roads and close to large patches of native forest, being almost exclusively restricted to this type of habitat. On the other hand, P. culpaeus preferred openhabitats, close to roads, relying extensively on pine plantations but scarcely using forest and forest fragments. Our results suggest that native forest fragmentation, considering habitat use only, would have a negative effect on O. guigna populations. Thus, forest size reduction and isolation may reduce O.guigna survival in a pine dominated landscape. In contrast, P. culpaeus, a generalist species that would use habitat depending on its abundance, may adapt to changes in this landscape.

Interspecific interactions between the native and introduced White‐eyes in the Bonin Islands

The impact of the introduced White‐eye Zosterops japonicus on the endemic White‐eye Apalopteron familiare was studied on Hahajima and Chichijima of the Bonin Islands. A. familiare preferred primary forests whereas Z. japonicus preferred open habitats, but their distribution greatly overlapped in secondary forests. The population density of A. familiare was stable whereas the Z. japonicus population had increased in number over the last 20 years, probably because of an increase in the area of open habitats. The data suggested that the population density of A. familiare had not been affected by the spreading Z. japonicus. The body weight of fledgling A. familiare was not affected significantly by the presence of Z. japonicus. Food items taken by A. familiare were similar to those of Z. japonicus. Where the species did not coexist, A. familiare foraged at all heights of the forest, but in the area of overlap, this species reduced its use of higher parts of the forest canopy where Z. japonicus foraged frequently. The food selection of A. familiare, however, did not change in the presence of Z. japonicus. This study detected almost no negative ecological relationship between Z. japonicus and A. familiare and suggests that competition is not a significant threat to either species. A. familiare may, if anything, benefit from Z. japonicus by forming a mixed‐species flock in the non‐breeding season.

Ontogenetic Behavior and Migration of Dabry's Sturgeon, Acipenser Dabryanus, from the Yangtze River, With Notes on Body Color and Development Rate

We conducted laboratory experiments with Dabry's sturgeon, Acipenserdabryanus, from the upper Yangtze River to develop a conceptual model of early behavior. We daily observed fish from day-0 (embryo, first life interval after hatching) to day-30 feeding larva for preference of bright habitat and cover, swimming distance above the bottom, up- and down-stream movement, and diel activity. Hatchling to day-12 embryos and days 13–24 larvae were similar for ontogenetic behavior, i.e., neither initiated a dispersal migration, both swam within 15 cm of the bottom, both preferred bright habitat, and neither strongly preferred cover or open habitat. Embryos and larvae were weakly active day and night. Days 72–76 juveniles had a weak nocturnal downstream migration, indicating wild juveniles disperse from a spawning site. In other sturgeon species yet studied representing three genera on three continents, Dabry's sturgeon is the first that does not disperse as an embryo or larva. Development of Dabry's sturgeon is slow, requiring more cumulative temperature degree days per millimeter of larvae TL than is required for other sturgeons to develop into larvae. Thus, a dispersal migration that diverts energy from development may not be adaptive. The available information suggests the initial dispersal of early life intervals is likely done by females, which spawn in a dispersed spawning style, not the usual aggregated spawning style. Juvenile migrants had a black body and tail with a light line along the lateral scutes. The color of juvenile migrants shows that a dark body and tail is characteristic of Acipenser that migrate downstream as larvae or juveniles.

Comparative Ontogenetic Behavior and Migration of Kaluga, Huso Dauricus, and Amur Sturgeon, Acipenser Schrenckii, from the Amur River

We conducted laboratory experiments with kaluga, Huso dauricus, and Amur sturgeon, Acipenser schrenckii, to develop a conceptual model of early behavior. We daily observed embryos (first life phase after hatching) and larvae (period initiating exogenous feeding) to day-30 (late larvae) for preference of bright habitat and cover, swimming distance above the bottom, up- and downstream movement, and diel activity. Day-0 embryos of both species strongly preferred bright, open habitat and initiated a strong, downstream migration that lasted 4 days (3 day peak) for kaluga and 3 days (2 day peak) for Amur sturgeon. Kaluga migrants swam far above the bottom (150 cm) on only 1 day and moved day and night; Amur sturgeon migrants swam far above the bottom (median 130 cm) during 3 days and were more nocturnal than kaluga. Post-migrant embryos of both species moved day and night, but Amur sturgeon used dark, cover habitat and swam closer to the bottom than kaluga. The larva period of both species began on day 7 (cumulative temperature degree-days, 192.0 for kaluga and 171.5 for Amur sturgeon). Larvae of both species preferred open habitat. Kaluga larvae strongly preferred bright habitat, initially swam far above the bottom (median 50-105 cm), and migrated downstream at night during days 10-16 (7-day migration). Amur sturgeon larvae strongly avoided illumination, had a mixed response to white substrate, swam 20-30 cm above the bottom during most days, and during days 12-34 (most of the larva period) moved downstream mostly at night (23-day migration). The embryo-larva migration style of the two species likely shows convergence of non-related species for a common style in response to environmental selection in the Amur River. The embryo-larva migration style of Amur sturgeon is unique among Acipenser yet studied.

Ontogenetic Behavior and Migration of Chinese Sturgeon, Acipenser sinensis

The Chinese sturgeon, Acipenser sinensis, is an anadromous protected species that presently only spawns in the Yangtze River. Using laboratory experiments, we examined the behavioral preference of young Chinese sturgeon to physical habitat (water depth, illumination intensity, substrate color, and cover) and monitored their downstream migration. Hatchling free embryos were photopositive, preferred open habitat, and immediately upon hatching, swam far above the bottom using swim-up and drift. Downstream migration peaked on days 0-1, decreased about 50% or more during days 2-7, and ceased by day 8. Days 0-1 migrants were active both day and night, but days 2-7 migrants were most active during the day. After ceasing migration, days 8-11 embryos were photonegative, preferred dark substrate and sought cover. Free embryos developed into larvae and began feeding on day 12, when another shift in behavior occurred-larvae returned to photopositive behavior and preferred white substrate. The selective factor favoring migration of free embryos upon hatching and swimming far above the bottom may be avoidance of benthic predatory fishes. Free embryos, which must rely on yolk energy for activity and growth, only used 19 cumulative temperature degree-days for peak migration compared to 234 degree-days for growth to first feeding larvae, a 1 : 12 ratio of cumulative temperature units. This ratio suggests that sturgeon species with large migratory embryos, like Chinese sturgeon, which require a high level of energy to swim during migration, may migrate only a short time to conserve most yolk energy for growth.

Characterization and Habitat Preferences by White-Tailed Deer in Mexico

We analyzed the habitat preferences of white-tailed deer in a 1,000 ha area in an arid region of northeastern Mexico where drinking water is abundant throughout the year (via 33 water troughs). Seven habitat types in the study area were identified and characterized. Within each habitat, feeding, searching, and bedding activities were evaluated during the reproduction, postreproduction and fawning seasons of the annual deer cycle. The Acacia-Celtis habitat provided the greatest amount of hiding and thermal cover and edible food. The Prosopis habitat also provided significant hiding and thermal cover. Hilaria and Opuntia were the most open habitats. Habitat preferences, evaluated by radiotracking 14 deer over a period of 2 years, varied between sexes and years (P 0.05). Male deer preferred open habitats, while females preferred more densely covered ones. Males and females avoided Prosopis during 1996. Both sexes distributed the 3 activities more evenly during 1996 than during 1995. In 1995, females preferred Flourensia and Acacia-Celtis habitats for all activities, and during 1996 males preferred Hilaria and Leucophyllum. Between year changes in precipitation could explain the observed variability: during 1995 rainfall was 136 mm, as compared to 276 mm in 1996. Requirements for cover increased markedly in 1995 due to high predation and extremely dry conditions. Overall, our study shows that under good weather conditions, habitat preferences are best explained by variables associated with food availability, while thermal cover is more important under harsh weather conditions, even when drinking water is abundant. DOI:10.2458/azu_jrm_v54i5_bello

Characterization and habitat preferences by white-tailed deer in Mexico

We analyzed the habitat preferences of white-tailed deer in a 1,000 ha area in an arid region of northeastern Mexico where drinking water is abundant throughout the year (via 33 water troughs). Seven habitat types in the study area were identified and characterized. Within each habitat, feeding, searching, and bedding activities were evaluated during the reproduction, postreproduction and fawning seasons of the annual deer cycle. The Acacia-Celtis habitat provided the greatest amount of hiding and thermal cover and edible food. The Prosopis habitat also provided significant hiding and thermal cover. Hilaria and Opuntia were the most open habitats. Habitat preferences, evaluated by radiotracking 14 deer over a period of 2 years, varied between sexes and years (P &lt;&lt; 0.00001), but not among seasons (P &gt; 0.05). Male deer preferred open habitats, while females preferred more densely covered ones. Males and females avoided Prosopis during 1996. Both sexes distributed the 3 activities more evenly during 1996 than during 1995. In 1995, females preferred Flourensia and Acacia-Celtis habitats for all activities, and during 1996 males preferred Hilaria and Leucophyllum. Between year changes in precipitation could explain the observed variability: during 1995 rainfall was 136 mm, as compared to 276 mm in 1996. Requirements for cover increased markedly in 1995 due to high predation and extremely dry conditions. Overall, our study shows that under good weather conditions, habitat preferences are best explained by variables associated with food availability, while thermal cover is more important under harsh weather conditions, even when drinking water is abundant.

Thermal Biology of the Australian Forest Dragon, Hypsilurus spinipes (Agamidae)

Unlike all other Australian agamid lizards, forest dragons (Hypsilurus spp.) are restricted to cool moist forest habitats where there is little light penetration and, thus, little opportunity for heliothermy. In keeping with this habitat preference, our field and laboratory studies of thermal availability and temperature selection reveal that Hypsilurus spinipes show little overt thermoregulatory behavior. Body temperatures of five radio-tracked lizards were low and variable (11-26 C), highly correlated (r > 0.96) with operative temperatures measured at the same time, and lower in the field than in a laboratory thermal gradient, where the lizards consistently avoided temperatures < 16 C. Quantitative analysis of perch-site characteristics, compared to availability, revealed minor but significant habitat selection (for high, vertical perches, of intermediate diameters, in areas with relatively open canopy) that may have elevated the lizards' body temperatures. Although other Australian agamid lizards differ from H. spinipes in their heliothermic behavior and preference for open habitats, they share a correlated suite of traits (e.g., ambush predation, reliance on camouflage to evade predators) that centers on prolonged immobility. These features are retained by H. spinipes in its densely forested habitat, where the high costs of heliothermy have favored a shift to extreme thermoconformity.

Sex Differences in Giraffe Feeding Ecology: Energetic and Social Constraints

AbstractSex ratios of giraffe groups differ in different habitats, with open vegetation having female‐biased groups, and tall, thick vegetation having male‐biased groups. On a ranch in south‐central Kenya, we quantified habitat differences of male and female giraffe groups and showed that the preference for open habitats by female groups was limited to groups with young. We suggest that this difference is due to the avoidance of predators of young giraffes. We also showed that rates of giraffe feeding peaked at intermediate feeding heights equal to approximately 60% of adult giraffe height. In the dense habitats with a variety of tree heights used by male groups and female groups without young, both male and female giraffes fed most at heights where they could feed fastest. However, in the open habitats used by female groups with young, females fed mostly at heights below optimum because these habitats are dominated by short food plants. On the other hand, the dominant males accompanying these female groups fed at heights above optimum on rare tall trees, possibly to increase intrasexual vigilance. Apparently, both male and female giraffes sometimes forfeit feeding efficiency tor short‐term reproductive gains.