Shade-seeking Behavior Research Articles

Leveraging camera traps and artificial intelligence to explore thermoregulation behaviour.

Behavioural thermoregulation has critical ecological and physiological consequences that profoundly influence individual fitness and species distributions, particularly in the context of climate change. However, field monitoring of this behaviour remains labour-intensive and time-consuming. With the rise of camera-based surveys and artificial intelligence (AI) approaches in computer vision, we should try to build better tools for characterizing animals' behavioural thermoregulation. In this study, we developed a deep learning framework to automate the detection and classification of thermoregulation behaviour. We used lizards, the Rough-tail rock agama (Laudakia vulgaris), as a model animal for thermoregulation. We colour-marked the lizards and curated a diverse dataset of images captured by trail cameras under semi-natural conditions. Subsequently, we trained an object-detection model to identify lizards and image classification models to determine their microclimate usage (activity in sun or shade), which may indicate thermoregulation preferences. We then evaluated the performance of each model and analysed how the classification of thermoregulating lizards performed under different solar conditions (sun or shade), times of day and marking colours. Our framework's models achieved high scores in several performance metrics. The behavioural thermoregulation classification model performed significantly better on sun-basking lizards, achieving the highest classification accuracy with white-marked lizards. Moreover, the hours of activity and the microclimate choices (sun vs shade-seeking behaviour) of lizards, generated by our framework, are closely aligned with manually annotated data. Our study underscores the potential of AI in effectively tracking behavioural thermoregulation, offering a promising new direction for camera trap studies. This approach can potentially reduce the labour and time associated with ecological data collection and analysis and help gain a deeper understanding of species' thermal preferences and risks of climate change on species behaviour.

Investigating the relationship between heat load and shade seeking behaviour in dairy buffaloes.

The study presented in this Research Communication aimed to investigate the relationship between physiological responses, body surface temperature and shade-seeking behaviour in Nili Ravi dairy buffaloes during summer months. We enrolled 60 buffaloes, and each animal was observed for three consecutive days starting before sunrise until they moved towards the shade structures. A repeated measures ANOVA was employed to assess the changes in physiological parameters and body surface temperature between the early morning and the occurrence of shade-seeking behaviour. The average temperature humidity index and heat load index during the behavioural monitoring period (0400 to 1200 h) were 81.3 ± 6.5 and 92.9 ± 17, respectively (mean ± sd). There was no significant difference in core body temperature between sunrise and the time of shade-seeking event. However, the buffaloes had a slightly higher respiration rate at the time of shade-seeking (19.2 vs. 22.4 breaths/min). In addition, body surface temperature, measured at the flank region, shoulder, base of the ear and forehead was significantly higher at the occurrence of shade-seeking behaviour compared to the early morning. On average, the buffaloes sought shade when the surface temperature was 2°C higher than the temperature recorded before sunrise. Overall, the current findings suggest that body surface temperature, rather than core body temperature was strongly associated with shade-seeking behaviour in dairy buffaloes. These findings could be useful in developing strategies to mitigate the effects of heat stress in dairy buffalo herds and thereby improve animal welfare.

State-dependent movement choices of desert lizards: The role of behavioural thermoregulation during summer and winter

Environmental temperatures are increasing worldwide, threatening desert ectotherms already living at their thermal limits. Organisms with flexible thermoregulatory behaviours may be able to mitigate the effects of extreme temperatures by moving among microhabitats, yet little work has tracked movement patterns of desert ectotherms in the wild over diurnal scales or compared behaviour among seasons. Here, we used camera traps to track the thermoregulatory behaviour and microhabitat choices of 30 desert lizards (Messalina bahaldini) in custom, outdoor arenas that provided access to open, rock, and bush microhabitats. We found that in the summer, lizards preferred to move to the shaded microhabitats and remain there under warmer conditions. During winter, however, lizards’ activity was not related to temperature, and lizards mostly chose to remain in the open habitat. Interestingly, in both seasons, lizards tended to remain in their current microhabitat and moved infrequently between certain combinations of microhabitats. Our study shows that thermoregulation (shade-seeking behaviour) is a major factor during summer, helping lizards to avoid extreme temperatures, but not during winter, and shows a novel effect of current microhabitat on movement, suggesting that other biotic or abiotic factors may also drive microhabitat choice. Understanding the complex factors at play in microhabitat choice is critical for developing conservation programs that effectively mitigate the negative impacts of climate change on desert animals.

Do sheep of different coat colors kept in an equatorial semi-arid environment use solar orientation behavior for thermoregulation?

Shade-seeking behavior and body posture adjustments are key thermoregulatory strategies used by free-ranging animals to minimize heat absorption. We observed these behaviors in grazing sheep, analyzing their orientation relative to solar radiation. Over seven days, we monitored six predominantly black and six white crossbred lambs. We found that shade-seeking behavior was less frequent on cloudy days (p < 0.05), with sheep spending more time grazing. Neither the black or the white sheep altered their body orientation to minimize heat absorption, regardless of sunny or rainy conditions. In conclusion, this preliminary investigation showed that body axis orientation seems not to be employed by black and white hair coat sheep as thermoregulatory strategy when exposed to solar radiation in an equatorial semi-arid environment.

The effect of shade on sheep grazing pasture during summer conditions

Providing shade in situ in paddocks may lead to better animal welfare and/or improved sheep production outcomes. However, there are no replicated experiments detailing the effect of the provision of shade in situ under grazing during summer on behavioral, physiological, and production outcomes of sheep in the scientific literature. This study uses a replicated field experiment to examine the effect of provision of shade in situ to sheep under grazing on animal behavior, respiration rate, core body temperature (CBT), growth, and immunological function during summer in south east Australia. The experiment consisted of eight unshaded pasture plots and eight shaded pasture plots with an 18 m2 shade structure. Each plot was stocked with 20 sheep. Sheep with access to shade chose to use the shade in the hottest part of the day, reducing their 12 pm respiration rate to 64 breaths per minute (bpm) compared with sheep without shade at 98 bpm (P < 0.0001). However, the provision of shade had no effect on CBT, immunological function, or animal production. In the hottest part of the day, sheep without shade exhibited shade seeking behavior by either being located along the fence line (P < 0.0001) or at the water trough (P < 0.001). In conclusion, provision of shade in situ to sheep under grazing during summer conditions improved the affective state, and thus welfare, of the sheep by reducing the respiration rate needed to maintain thermostability.

Identification of Relevant Sociocognitive Determinants Explaining Multiple Parental Sun Protection Behaviors.

BackgroundAdequate sun safety during childhood is crucial for decreasing skin cancer risk in later life. Although parents are an essential target group in applying sun protection measures for their children, insight into the determinants associated with their sun protection behaviors is limited.AimsThis study aims to identify the most relevant determinants in predicting multiple parental sun protection intentions and behaviors in different sun exposure situations.MethodA longitudinal survey study with two measurements was conducted among Dutch parents (N = 670) of children (4–12 years old). Twenty-seven sociocognitive determinants were examined in terms of relevance regarding four parental sun protection behaviors in different sun exposure situations. The Confidence Interval-Based Estimation of Relevance approach was used to visualize room for improvement (sample means) on all determinants and their association strengths (correlations) with sun protection intentions and behaviors.ResultsBehavior-specific rather than generic determinants were most relevant in explaining all sun protection behaviors. Of these determinants, attitude, self-efficacy and action planning, and especially parental feelings of difficulty in performing sun protection behaviors, were most relevant. Altogether, the explained variance of all sociocognitive determinants was highest for shade-seeking behavior (R2 = .41 and .43) and lowest for supportive behavior (R2 = .19 and .29) in both planned and incidental sun exposure situations, respectively.DiscussionThis study provides detailed insight into relevant sociocognitive determinants of parental sun protection behaviors in various sun exposure situations and directions for composing parental skin cancer prevention interventions.ConclusionsFuture composition of sun safety interventions should emphasize on enhancing parental feelings of self-efficacy, especially for shade-seeking and clothing behaviors.

Shade-seeking behavior and grazing activity of Pantaneira and Girolando heifers.

This study aimed to model and compare the shade-seeking behavior and grazing activity of Pantaneira and Girolando heifers by time of day. Eight heifers were used, four Pantaneira and four Girolando (3/4 Holstein × 1/4 Gir). The animals were about 18months old and weighed 328 ± 14kg (Pantaneira) and 430 ± 28kg (Girolando). Shade-seeking behavior and grazing activity were recorded during the summer from 06:00 to 18:00h in 10-min intervals, totaling 288 observations for each breed. A binary regression model was developed by means of a Bayesian approach considering logit, probit, cloglog, and Cauchy link functions. The most parsimonious model was constructed using the Cauchy function. The variables varied according to the time of day. Heifers of both breeds were more likely to graze toward the end of the day, when ambient temperatures were lower. Girolando heifers were more likely to seek shade between 06:00 and 14:00h. From 12:00 to 13:00, the probability of seeking shade between breeds differed 22 percentage points. Pantaneira heifers were more likely to graze from 06:00 to 13:00h, and their probability of grazing at 11:00h was 21 percentage points higher than that of Girolando heifers. The results suggest that Pantaneira heifers are more heat-tolerant.

Mapping Shade Availability and Use in Zoo Environments: A Tool for Evaluating Thermal Comfort.

Simple SummaryThe thermal environment experienced by animals in zoos has implications for their comfort, and ultimately welfare. In this study, we describe a simple low-cost approach to documenting one key aspect of the environment, shade, and its use by animals. We share a successive approach that can be adopted based on an organization’s capacity: Ranging from simple mapping of shade availability in enclosures that can be built upon to incorporate more advanced tracking of space use by animals and detailed assessment of shade use. Using these methods, we discovered shade availability at a zoo in a northern continental climate varied greatly across enclosures, as well as by season and time of day. We present a case study on Sichuan takin to highlight the applied potential of this approach. Relying on insights from a combination of shade and behavioral data, a shade structure was installed and then evaluated for this species. As zoos seek to create enclosures that promote positive welfare, careful consideration should be paid to the thermal environment and choices available to animals. We share these accessible methods to encourage others to evaluate shade and its use by zoo animals.For many species in zoos, particularly megafauna vulnerable to heat stress, shade is a key environmental resource. However, shade availability has received comparatively less attention than other aspects of the zoo environment. In this study, we share a simple low-cost approach that we applied to document shade availability across 33 zoo enclosures. We then combined these assessments with behavioral observations of enclosure use and shade-seeking behavior during summer months in a case study focused on Sichuan takin (Budorcas taxicolor tibetana) (n = 3), a large cold-adapted bovid. Behavioral observations were conducted before and after installation of a shade sail for the takin. Results indicated that shade availability varied widely across zoo enclosures, with the percent of shaded space ranging from 85 % to 22 % across enclosures during summer months. Shade was a dynamic resource and increased throughout the year and fluctuated across the day, with the least shade available midday. Takin showed general preferences for shaded areas near the walls of their enclosure but were observed using newly available shade from the shade sail after its installation. These accessible methods can be easily applied to assess shade within existing enclosures, evaluate enclosure modifications, and provide guidance for the design of new enclosures.

Are Environmental Interventions Targeting Skin Cancer Prevention among Children and Adolescents Effective? A Systematic Review.

Skin cancer, which is increasing exceedingly worldwide, is substantially preventable by reducing unprotected exposure to ultraviolet radiation (UVR). Several comprehensive interventions targeting sun protection behaviors among children and adolescents in various outdoor settings have been developed; however, there is a lack of insight on stand-alone effectiveness of environmental elements. To compose future skin cancer prevention interventions optimally, identification of effective environmental components is necessary. Hence, an extensive systematic literature search was conducted, using four scientific databases and one academic search engine. Seven relevant studies were evaluated based on stand-alone effects of various types of environmental sun safety interventions on socio-cognitive determinants, sun protection behaviors, UVR exposure, and incidence of sunburns and nevi. Free provision of sunscreen was most often the environmental component of interest, however showing inconsistent results in terms of effectiveness. Evidence regarding shade provision on shade-seeking behavior was most apparent. Even though more research is necessary to consolidate the findings, this review accentuates the promising role of environmental components in skin cancer prevention interventions and provides directions for future multi-component sun safety interventions targeted at children and adolescents in various outdoor settings.

Protection from Ultraviolet Radiation during Childhood: The Parental Perspective in Bavaria.

During childhood, parents play a vital role in sun protection of their children. Their guidance is essential for avoiding excessive exposure to ultraviolet (UV) radiation, a risk factor for developing skin cancer in later life. In a population-based cross-sectional study conducted between October 2011 and February 2012, we assessed how 3281 parents implemented sun protection for their three- to six-year-old children in practice. In particular, clothing, shade-seeking behavior, wearing of sunhats and sunglasses, use of sunscreens and the amount of time spent outdoors were ascertained in two settings (beach, garden/playground). The results showed that the overall level of parental sun protection for their children in the beach setting, and to a lesser extent also in the everyday outdoor setting, is relatively high. Using sunscreens with a high sun protection factor and instructing children to wear a sunhat were very common. Lesser attention was paid to sun-protective clothing, seeking the shade and wearing sunglasses. The amount of time spent outdoors during summer days was high. Therefore, the recommendation to completely avoid sun exposure during peak UV times around noon during summertime needs to be reinforced. In addition, the observed difference in the protective behavior between the beach and an everyday outdoor setting points to the necessity to encourage better sun protection for children also in outdoor activities of daily living.

A continent-wide analysis of the shade requirements of red and western grey kangaroos

ABSTRACTForaging time may be constrained by a suite of phenomena including weather, which can restrict a species' activity and energy intake. This is recognized as pivotal for many species whose distributions are known to correlate with climate, including kangaroos, although such impacts are rarely quantified. We explore how differences in shade seeking, a thermoregulatory behavior, of 2 closely-related kangaroo species, Macropus rufus (red kangaroos) and M. fuliginosus (western grey kangaroos), might reflect differences in their distributions across Australia. We observed foraging and shade-seeking behavior in the field and, together with local weather observations, calculated threshold radiant temperatures (based on solar and infrared radiant heat loads) over which the kangaroos retreated to shade. We apply these calculated tolerance thresholds to hourly microclimatic estimates derived from daily-gridded weather data to predict activity constraints across the Australian continent over a 10-year period. M. fuliginosus spent more time than M. rufus in the shade (7.6 ± 0.7 h versus 6.4 ± 0.9 h) and more time foraging (11.8 ± 0.5 h vs. 10.0 ± 0.6 h), although total time resting was equivalent (∼8.2 h). M. rufus tolerated 19°C higher radiant temperatures than M. fuliginosus (89°C versus 70°C radiant temperature). Across Australia, we predicted M. fuliginosus to be more restricted to shade than M. rufus, with higher absolute shade requirements farther north. These results corroborate previous findings that M. rufus is more adept at dealing with heat than M. fuliginosus and indicate that M. rufus is less dependent on shade on a continental scale.

Black wildebeest seek shade less and use solar orientation behavior more than do blue wildebeest

Many ungulates, including wildebeest, seek shade and orient their bodies relative to incoming solar radiation in order to reduce environmental heat loads. Blue (Connochaetes taurinus) and black wildebeest (Connochaetes gnou), which co-exist artificially in some reserves in South Africa, are thought to adopt different thermoregulatory behaviors to mitigate high environmental heat loads. However, whether or not blue and black wildebeest use different behaviors to reduce heat loads in regions where they co-occur has never previously been examined. We compared the shade seeking and solar orientation behavior of free-ranging blue and black wildebeest in summer at three locations in South Africa where both species co-occur. We found that blue wildebeest exhibited more shade seeking behavior than did black wildebeest at all times of day, at all study sites. Black wildebeest remained in the sun but were more likely than blue wildebeest to orient their bodies parallel to the sun at all study sites, a behavior which reduces the amount of surface area exposed to incoming radiation. Black wildebeest were most likely to employ parallel solar orientation during the hottest times of the day when the sun was not directly overhead (i.e., solar noon ± 1 hour). We thus demonstrate that co-occurring blue and black wildebeest use different thermoregulatory behaviors to reduce high heat loads. It is possible that the lack of shade in the historical distribution of black wildebeest led to selective pressure for reliance on solar orientation. Differences in thermoregulatory behavior can affect species-specific heat loads, habitat use, body mass, fitness and grazing activity. Such differences may also allow blue and black wildebeest to inhabit separate microclimates within the same habitat, provided there is sufficient heterogeneity in vegetation structure, potentially facilitating reproductive isolation.

Effects of solar ultraviolet radiation on the behaviour of juvenile coho salmon (Oncorhynchus kisutch): avoidance, feeding, and agonistic interactions

The behaviour of juvenile coho salmon (Oncorhynchus kisutch) was observed in outdoor experimental flumes in which three different spectral regimes were created by plastic covers that selectively blocked all or portions of natural ultraviolet radiation (UVR). The three light treatments were (i) photosynthetically active radiation (PAR, 400–700 nm), (ii) PAR plus longer wavelength ultraviolet (PAR + UVA, 320–700 nm), and (iii) full-spectrum sunlight with both long and short wavelength ultraviolet included (PAR + UVA + UVB, 280–700 nm). Observations made at different times of the day and under both overcast and sunny skies allowed an assessment of PAR intensity on behaviour in addition to that of UVR. We quantified shade-seeking behaviour, feeding strikes, and agonistic interactions (approaches, chases, and nips) between individuals. Under higher PAR intensities, a greater proportion of juvenile coho tended to take cover under rocks. Shade-seeking behaviour increased significantly in the presence of UVR. Feeding and agonistic interactions were partially inhibited at higher PAR intensities and very significantly depressed by UVR. For all behaviours tested, the effects were mediated by UVA with no significant additional impacts from UVB. UVR-mediated effects on behaviour could have ecological consequences through influencing summer densities, density-dependent growth, and size-dependent winter and early marine survivals.

Avoidance of solar ultraviolet radiation by juvenile coho salmon (Oncorhynchus kisutch)

Shade-seeking behavior and avoidance of solar ultraviolet radiation (UVR) by newly emerged coho salmon (Oncorhynchus kisutch) alevins and two-month-old coho juveniles was documented in experimental trials in the Little Qualicum River, British Columbia, using outdoor chambers that provided the fish with a binary choice of photo environments. Under high solar intensities (i.e., midsummer, cloudless skies) coho of both age classes strongly preferred 50% neutral density shaded conditions to unattenuated full-spectrum (280–700 nm) sunlight (t test, p &lt; 0.025). In addition, coho alevins and juveniles showed a high selective avoidance of UVR (280–400 nm) (t test, p &lt; 0.05). Within the UVR spectrum, coho responded significantly to UVA (320–400 nm) (t test, p = 0.028). Evidence of UVB (280–320 nm) avoidance was confounded by higher visible and UVA irradiance levels under screens exposing coho to UVB. Under lower solar intensities (i.e., cloudy skies) coho showed no spectral preference and did not seek neutral density shade. Behavioral avoidance of high intensity UVR, particularly UVA, suggests that shade-seeking behavior of juvenile coho may be linked to avoiding potentially harmful UVR exposure.

Thermal ecology of Zonocerus variegatus and its effects on biocontrol using pathogens

Summary 1 Thermal behaviour of the variegated grasshopper, Zonocerus variegatus, was investigated in the humid tropical zone of southern Benin, west Africa, in the dry seasons of 1996 and 1998. In 1998, investigations included studies of a population of grasshoppers sprayed with an oil-based formulation of the entomopathogenic fungus Metarhizium anisopliae var acridum. 2 Body temperature measurements and observations of thermal behaviour both in the field and on thermal gradients in the laboratory, suggest that Z. variegatus was not an active behavioural thermoregulator. Although it did show shade-seeking behaviour at high temperatures, no overt behavioural postures or microhabitat selection associated with heat gain and elevation of body temperatures was observed. Moreover, no alterations to thermal behaviour were found in response to infection by Metarhizium. 3 Body temperatures exhibited by Z. variegatus in the field will lengthen disease incubation of M. anisopliae var acridum compared with laboratory maintained, constant temperature conditions and may have a significant impact on pathogens with a lower thermal tolerance. 4 Habitat structure appeared to be an important factor determining the extent of body temperature elevation. The effect of habitat differences on infection and growth of M. anisopliae var acridum and other entomopathogenic fungi is discussed.

Shade-seeking behaviour under polarized light by the brittlestar Ophioderma Brevispinum (Echinodermata: Ophiuroidea)

The effect of polarized light on the shade-seeking behaviour of the ophiuroid Ophioderma brevispinum was investigated at the Keys Marine Laboratory, Long Key, Florida, USA. Animals were collected and placed in a partially shaded arena. When the arena was illuminated with unpolarized light, the number of animals settling under the shaded portion of the arena was not significantly different from random (N=30, P&gt;0.3). When the arena was illuminated with linearly polarized light, the number of animals settling in the shaded portion of the arena was approximately double what would be expected in a random distribution (N=30, P&lt;0.001). The results are further evidence that O. brevispinum is sensitive to polarized light and are consistent with the hypothesis that polarized light may be used by the animals as an indicator of harmful levels of solar ultraviolet radiation.

The thermoregulatory advantages of heat storage and shade-seeking behaviour to hominids foraging in equatorial savannah environments

Despite the lack of an elaborate brain cooling system, early hominids could probably tolerate slight fluctuations in body temperature, comparable to those experienced by living primates in thermally stressing environments. Estimates are presented of the reductions in drinking water requirements resulting from the use of such heat storage, both of hominids foraging continually throughout the day on the open savannah, and those suspending this behaviour during the most thermally stressing period. The findings show that periods of inactivity can offer substantial thermoregulatory benefits, but only if the animal is able to retreat into the shade. Both strategies appear to be most advantageous in the absence of functional body hair. Together heat storage and shade-seeking can reduce the estimated total daytime drinking water intakes of naked bipeds to less than one half of those maintaining a constant body temperature and remaining continually active in the open. These studies of activity, patterns likely to have been more typical of those normally utilised when foraging on the open savannah, suggest that the selection pressures favouring the evolution of a functionally naked skin by these bipedal primates may have been even greater than previous calculations based solely on continually active hominids indicated.

Shade-seeking and lying behaviour in pigs of mixed sex and age, with access to outside pens

Observations were made over a 2 month period (50 days) of the standing, lying and shade-seeking behaviour of boars, sows, growers and weaners with access to an outside pen. Some pigs sought shade between 15 and 20°C, and by 26–30°C nearly all the boars (88.3%), sows (87.3%) and growers (91.2%) were in the shade. However, only 65.4% of the weaners were in the shade. Above 35°C, the proportion of weaners seeking shade had increased to 85%. At the lower temperatures (15–20°C) most of the sows in the shade were lying down (84.7%), but only 13.3% of the boars, 54.8% of weaners and 67.6% of growers were lying in the shade. Above 35°C, almost all sows and boars in the shade were lying down (99.6% and 97.9%, respectively) and many of the growers (93.9%) and weaners (91.1%). The younger animals were more restless or lacked the experience to seek shade, either standing or lying down. The proportion of all pigs in the sun (standing or lying) in the morning (08:00–12:00 h) was negatively related to temperature ( P < 0.01) and there was no relation with time. In the afternoon (13:00–16:00 h), ambient temperature was not related to the proportion of pigs in the sun, however, time of day showed a weak correlation for boars, sows and weaners, but not for growers. In the morning (08:00–12:00 h) and afternoon (13:00–16:00 h), the proportion of animals standing was related to time rather than temperature. In the morning, the proportion standing decreased and in the afternoon increased with advancing time. If access to outdoors becomes an alternative pig husbandry system, consideration should be given to provision of shade in temperatures above 20°C.

Physiologically based landscape use model for large herbivores

This paper describes the development and initial validation of a simulation model designed to predict patterns of landscape use by cattle as a function of environmental conditions and spatial distribution of key landscape attributes. The model consists of environmental, physiological, behavioral, and landscape submodels. Information on climatic conditions from the environmental submodel is used by the physiological submodel to determined current physiological status of animals in terms of heat balance, water balance, and hunger status. Information on physiological status is used by the behavioral submodel to select and subsequently perform activities. Performance of activities then affects physiological state. The landscape submodel provides information concerning spatial relationships among and within different habitat patches. Landscape attributes influence animal behavior, and animal behavior then influences landscape characteristics. Several aspects of model performance were evaluated using new field data and literature information. Predicted animal water losses via respiration, sweat, urine, and feces, total time spent in various daily activities, and the sequence of these activities all are in general agreement with field data and literature information. However, more accurate prediction of respiration rate, which controls shade seeking behavior in the model, may require more sophisticated representation of the combined effect of temperature and relative humidity. Initial simulations, which examined seasonal differences in the effect of distance between shade and water on landscape use, demonstrated the capability of the model to address a wide variety of questions concerning utilization of heterogeneous landscapesby grazing animals.

Relative Abundance of Day-Flying Insects in Treefall Gaps vs Shaded Understory in a Neotropical Forest

Day-flying insects were sampled in treefall gaps and closed understory within the semideciduous, lowland forest of Barro Colorado Island, Panama, from April (late dry season) to August (mid wet season) in 1980. Transparent strips of plastic coated with tanglefoot were suspended above ground at 5 treefall and 5 understory sites. Traps were run from early morning to late afternoon for 4-day periods at approximately 2-wk intervals. For most taxa, the numbers of individuals captured were relatively low during the first sampling period (prior to the onset of heavy rains), increased to peak levels between mid-May and mid-June, and then declined slightly in July and August. Statistically significant differences in abundance between gap and understory sites were noted only for Formicidae, Coleoptera, and Psocoptera. In all 3 cases, greater numbers of individuals were trapped at understory sites. Size frequency distributions were similar between treefall gaps and understory for all taxa. A PROMINENT FEATURE OF MANY TROPICAL FORESTS iS structural heterogeneity resulting from the occurrence of treefall gaps. Gaps of varying sizes and ages frequently interrupt the shaded understory and create conspicuously distinct habitat patches within many tropical forests (Halle et al. 1978, Whitmore 1978, Lang & Knight 1983). Vegetational differences between treefall gaps and the closed understory frequently have been reported (Oldeman 1978, Denslow 1980), and the role of treefall gaps in tropical forest dynamics has received considerable attention recently (Hartshorn 1980, Foster & Brokaw 1982, Brokaw 1985). In contrast, the influence of treefall gaps upon the structure of animal communities is poorly understood. Schemske and Brokaw (1981) censused birds in treefall gaps and adjacent forest in central Panama and found pronounced differenes in species richness and composition. Working in the same region, I described distinct lightand shadeseeking behavior of adult damselflies (Shelly 1982) and robber flies (Shelly 1984, 1985), both sit-and-wait predators that attempt aerial capture of flying insects. For both taxa, certain species were found to perch and forage primarily within the shaded understory, whereas others were found almost exclusively in light gaps. Recognition of these lightand shade-seeking guilds, coupled with additional behavioral and ecological observations, raised questions regarding possible differences in the spectra of available prey between treefall gaps and closed understory. The great majority of studies involving large-scale sampling of insects within tropical habitats does not deal with the day-flying, aerial fauna. Instead, most prior studies sample insects in one of these modes: attracted to lights at night (Wolda 1978, Wolda & Fisk 1981); resting on vegetation by sweeping, beating, or fogging (Janzen 1973, Janzen & Pond 1975); occurring in leaf litt r or in the soil (Levings & Windsor 1985); attracted to mammalian baits (Goodier 1966, Clarke 1968); attracted to rotting fruit (Dobzhansky & Pavan 1950, Owen & Chanter 1972); or attracted to pheromone baits (Ackerman 1983, Greenfield 1983). Malaise traps have been used successfully in some studies (Owen & Chanter 1970, Denlinger 1980), but the collections may have been highly site-dependent, since only one or two traps were operated in fixed locations. Additionally, of course, Malaise traps capture both dayand night-flying insects. Other methods previously used to sample day-flying insects in tropical habitats include tow-netting (Hespenheide 1975), yellow water traps (Duviard & Pollett 1973), window pane traps (Robinson & Robinson 1973), sticky traps (Robinson & Robinson 1973), and suction traps (Bigger & Tapley 1969, Rose 1972). However, in none of these studies (or those using Malaise traps) was an attempt made to systematically sample and compare treefall gaps and understory within primary forest. Moreover, in a number of these studies (Bigger & Tapley 1969, Owen & Chanter 1970, Rose 1972), samples were taken in urban or agricultural areas. The present study provides the results of a sampling program designed to compare the relative abundance of day-flying insects in treefall gaps vs shaded understory in a lowland Neotropical forest. Data regarding seasonal trends in abundance and size distributions are presented as well. Insects were sampled using transparent, tanglefoot-covered traps suspended above the ground. Although this method unquestionably yields biased samples (discussed below), the use of tanglefoot traps was considered justified for five reasons: their low cost (in both dollars and labor) of construction, shipping, and maintenance; their light weight and portability; their presumably nonattractive nature that allows collection of site-specific samples; their ease of opI Received 31 March 1986, revision accepted 11 September 1986. 114 BIOTROPICA 20(2): 114-119 1988 This content downloaded from 157.55.39.35 on Fri, 02 Sep 2016 05:39:13 UTC All use subject to http://about.jstor.org/terms eration by a single person; and the reproducibility of the sampling protocol. Additionally, although canopy insects may be abundant within tropical forests (Sutton & Hudson 1980), sampling in the present study was confined to the ground level for logistic reasons.