Individual Butterfly Research Articles

MSAIL: Milligram-Scale Multi-Modal Sensor Platform for Monarch Butterfly Migration Tracking

Each fall, millions of monarch butterflies across the northern US and Canada migrate up to 4,000km to overwinter in specific mountain peaks in central Mexico. To track monarchs precisely and study their navigation, a monarch tracker must obtain daily localization of the butterfly as it progresses on its three-month journey. And, the tracker must perform this task while having a weight in the tens of milligrams (mg) and measuring a few millimeters (mm) in size to avoid interfering with the monarch's flight. This paper proposes mSAIL, 8 × 8 × 2.6mm and 62mg embedded system for monarch migration tracking, constructed using 8 prior custom-designed ICs providing solar energy harvesting, an ultra-low power processor, light/temperature sensors, power management, and a wireless transceiver, all integrated and 3D stacked on a micro PCB with an 8 × 8mm printed antenna. The proposed system is designed to record and compress light and temperature data during the migration path while harvesting solar energy for energy autonomy, and wirelessly transmit the data at the overwintering site in Mexico, from which the daily location of the butterfly can be estimated using a deep learning-based localization algorithm. A two-day trial experiment of mSAIL attached to a live butterfly in an outdoor botanical garden demonstrates the feasibility of individual butterfly localization and tracking.

Winter Rains Support Butterfly Diversity, but Summer Monsoon Rainfall Drives Post-Monsoon Butterfly Abundance in the Arid Southwest of the US.

Butterfly populations are declining worldwide, reflecting our current global biodiversity crisis. Because butterflies are a popular and accurate indicator of insect populations, these declines reflect an even more widespread threat to insects and the food webs upon which they rely. As small ectotherms, insects have a narrow range of habitable conditions; hence, extreme fluctuations and shifts caused by climate change may increase insects' risk of extinction. We evaluated trends of butterfly richness and abundance and their relationship with relevant climate variables in Arizona, U.S.A., using the past 40 years of community science data. We focused on precipitation and temperature as they are known to be influential for insect survival, particularly in arid areas like southwestern U.S.A. We found that preceding winter precipitation is a driver of both spring and summer/fall butterfly richness and spring butterfly abundance. In contrast, summer/fall butterfly abundance was driven by summer monsoon precipitations. The statistically significant declines over the 40-year period were summer/fall butterfly abundance and spring butterfly richness. When controlling for the other variables in the model, there was an average annual 1.81% decline in summer/fall season butterfly abundance and an average annual decline of 2.13 species in the spring season. As climate change continues to negatively impact winter precipitation patterns in this arid region, we anticipate the loss of butterfly species in this region and must consider individual butterfly species trends and additional management and conservation needs.

Wing morphology and eyespot pattern of Erebia medusa (Lepidoptera, Nymphalidae) vary along an elevation gradient in the Carpathian Mountains

Wing morphology and eyespot pattern of Erebia medusa (Lepidoptera, Nymphalidae) vary along an elevation gradient in the Carpathian Mountains

Butterfly abundance and presence of their host plant at Bantimurung-Bulusaraung National Park, Indonesia

The famous butterfly conservation areas in South Sulawesi, Bantimurung-Bulusaraung National Park, are gradually being replaced by intensively used farmland especially in lowland and submontane regions. The objectives of the research were to identify butterfly species and their host plant served as larvae food, nectar and pollen source in three different altitudes at Bantimurung-Bulusaraung National Park. The research was conducted based on transect methods at Bantimurung-Bulusaraung National Park, Maros Regency, South Sulawesi, Indonesia from April to October 2018. Butterflies and their food were observed in three locations at different altitudes of 0-300 m above sea level (asl), 400-700 m asl, and above 700 m asl. The observation indicates a variation in the butterfly species found in different altitudes based on the presence of host plants. A total of 59 individual butterfly samples collected were divided into four families: Papilionidae (7 species), Pieridae (2 species), Nymphalidae (1 species) and Saturniidae (1 species). A further dispersal study based on seasons is needed in order to build a good taxonomic database for Sulawesi butterflies conservation.

Features of Spatiotemporal Clustering in a Maunder Butterfly Diagram

The Maunder butterfly pattern is the most complete spatial-temporal representation of observed changes in solar activity in the 11-year cycle over a period of 12–24 cycle. The well-known empirical relation is used to transform Greenwich sunspot areas into magnetic flux, and the distances between the butterfly wings are then calculated with the Fisher–Rao metric. We found that the similarities or differences in the patterns of the individual butterfly wings in this metric are approximately the same for each hemisphere. The wings were the closest for a sequence of strong cycles, while there is a tendency for a series of weak cycles to form cycles in pairs with the implementation of an analog of the Gnevyshev–Olya rule.

Effects of organic farming on plant and butterfly functional diversity in mosaic landscapes

Organic farming can benefit plants and butterflies in terms of species richness and abundance, in particular in homogeneous landscapes. Nevertheless, whether organic farming can benefit functional diversity of these two organism groups is not well understood. Organic farming could benefit functional diversity by counteracting simplification and homogenisation of biotic communities caused by earlier agricultural intensification, and therefore contribute to communities more resilient to environmental or land use changes. We analysed species richness and four functional diversity indices (functional richness, evenness, divergence and dispersion) of plants and butterflies on 15 pairs of organic/conventional farms in North-West Spain, whilst accounting for independent and joint effects of landscape context. To better understand links between functional diversity and taxonomic species assemblages, we applied an indicator species analysis to determine whether any particular plant or butterfly species were significantly more abundant on organic or conventional farms. Both butterfly species and functional richness were higher on organic than on conventional farms. In addition, when the farms were surrounded by low proportions of agriculture, butterfly functional evenness was higher on organic farms. In contrast, organic farming did not affect plant species richness or functional diversity. Nevertheless, plants were affected by landscape openness and field size, so that plant functional richness decreased with increasing landscape openness while functional evenness showed a complex relationship to the interaction between field size and landscape openness. Indicator analyses revealed that three plant species, but no individual butterfly species, were significantly related to organic farming. In conclusion, organic farms provide higher-quality habitat for butterflies than conventional farms, either by promoting specific grassland plants benefiting butterflies, or more generally by providing a wider niche space, fostering functionally diverse butterfly communities.

Geomorphic Morphometric Differences between Populations ofSpeyeria diana(Lepidoptera: Nymphalidae)

The wing shape of butterflies can be used as a character to measure individual butterfly and population-level differences in adult forms. We conducted a geometric morphometric analysis of wing shape for Speyeria diana (Cramer & Stoll 1777) (Lepidoptera: Nymphalidae), a species currently threatened by extirpation across portions of its range. We photographed and digitized 243 pinned S. diana specimens from natural history museums in North America and Europe to compare wing shape and size across the historical and current distribution. We used principal components analysis (PCA) to compare variation in landmarks on forewings and hind wings. We used the principal component scores in a multiple analysis of variance (MANOVA) to test for differences, and interactions, between male and female specimens, eastern and western specimens, low and high elevation specimens, and specimens collected before and after 1950. We found significant differences between wing shape in male and female specimens, with male forewings being narrower and more elongated, possibly making them well suited for patrolling behavior. Female forewings were more rounded and wider, possibly reflecting their life history, because much of their life is spent on the forest floor in search of oviposition sites. We found significant regional differences in male forewing shape, reflecting the long-term geographic and genetic separation between these groups. We also found significant differences in female forewing shape between low and high elevation sites. Speyeria diana female forewings from high elevation populations were narrower than low elevation populations, indicating that these females may be more mobile than those from low elevations with wider forewings. There were no effects of yr since capture of specimens. The wing shape of western populations of S. diana appears to be adapted for low dispersal, supporting other recent findings that also indicate western populations of S. diana are both spatially and genetically isolated. We conclude that the future of S. diana will require the thoughtful preservation of well-connected high elevation habitats, especially in the western distribution where dispersal is more limited than in the east.

The first red list of Italian butterflies

Abstract The Italian biodiversity is among the richest in Europe. In particular, the Italian butterfly fauna includes almost 300 native species, and within the Euro‐Mediterranean area is second in species richness only to Turkey. Italy, however, has suffered from the lack of suitable instruments to evaluate the extinction risk of individual butterfly species on the basis of internationally recognised standards. We have been working to create the first Italian Red List for butterflies. The achievement of this goal was divided into three actions: (i) the institution of a network of experts on butterfly conservation; (ii) the evaluation of the extinction risk for all Italian butterfly species; (iii) the integration of the baseline information provided by the Italian Red Lists of other taxa crucial for future evaluations of biodiversity trends in Italy. Assessments of extinction risks were based on the IUCN Red List Categories and Criteria following their most updated guidelines and were discussed during workshops involving experts from different Italian regions. All native Italian butterflies were included in the evaluation. The whole national population of each species was evaluated, including those on large and small islands. Of 289 butterfly species assessed, one has become Regionally Extinct recently. Threatened species are 18 in total, corresponding to 6.3% of the species assessed. The majority of Italian butterfly populations are stable. The main threats to Italian butterflies are natural reforestation, as a consequence of rural land abandonment, agricultural intensification and climate change for species living at high altitude.

Disperse or die: Colonisation of transient open habitats in production forests is only weakly dispersal-limited in butterflies

Evaluating ecological processes that assemble local animal communities from available species pools has remained a challenging task. At a time of drastic decline of natural and seminatural grasslands, contemporary production forests provide various novel types of open spaces (clear-cuts, power line corridors, etc.) that are potentially suitable habitats for many grassland species, such as butterflies. On the other hand, grassland butterflies are known to perceive forest as a dispersal barrier, potentially limiting the utility of such alternative habitats. We evaluated the role of dispersal limitation in structuring local butterfly assemblages in conventionally managed forest landscapes in which clear-cutting generates varyingly isolated transient open habitats within the forest matrix. We compared butterfly species richness and composition in clear-cuts at opposite ends of a connectivity gradient: sites completely surrounded by forest (isolated clear-cuts) vs. sites connected to the network of other forest clearings by open corridors (non-isolated clear-cuts). We found only a slight difference in the species richness between isolated and non-isolated clear-cuts, both when all open-habitat species and when the subset of grassland species was compared. The frequencies of individual butterfly species in isolated and non-isolated sites were strongly correlated, regardless of their presumed dispersal ability. Our results indicate that, in large areas of production forests in Northern Europe, the formation of local butterfly assemblages is not significantly limited by dispersal. This study contributes to emerging evidence that open spaces in managed forest landscapes can be regarded as alternative habitat for a substantial share of species traditionally considered to be associated with grasslands.

Efficient Strategies for Calculating Blockwise Likelihoods Under the Coalescent.

The inference of demographic history from genome data is hindered by a lack of efficient computational approaches. In particular, it has proved difficult to exploit the information contained in the distribution of genealogies across the genome. We have previously shown that the generating function (GF) of genealogies can be used to analytically compute likelihoods of demographic models from configurations of mutations in short sequence blocks (Lohse et al. 2011). Although the GF has a simple, recursive form, the size of such likelihood calculations explodes quickly with the number of individuals and applications of this framework have so far been mainly limited to small samples (pairs and triplets) for which the GF can be written by hand. Here we investigate several strategies for exploiting the inherent symmetries of the coalescent. In particular, we show that the GF of genealogies can be decomposed into a set of equivalence classes that allows likelihood calculations from nontrivial samples. Using this strategy, we automated blockwise likelihood calculations for a general set of demographic scenarios in Mathematica. These histories may involve population size changes, continuous migration, discrete divergence, and admixture between multiple populations. To give a concrete example, we calculate the likelihood for a model of isolation with migration (IM), assuming two diploid samples without phase and outgroup information. We demonstrate the new inference scheme with an analysis of two individual butterfly genomes from the sister species Heliconius melpomene rosina and H. cydno.

Coexistence of both gyroid chiralities in individual butterfly wing scales of Callophrys rubi

The wing scales of the Green Hairstreak butterfly Callophrys rubi consist of crystalline domains with sizes of a few micrometers, which exhibit a congenitally handed porous chitin microstructure identified as the chiral triply periodic single-gyroid structure. Here, the chirality and crystallographic texture of these domains are investigated by means of electron tomography. The tomograms unambiguously reveal the coexistence of the two enantiomeric forms of opposite handedness: the left- and right-handed gyroids. These two enantiomers appear with nonequal probabilities, implying that molecularly chiral constituents of the biological formation process presumably invoke a chiral symmetry break, resulting in a preferred enantiomeric form of the gyroid structure. Assuming validity of the formation model proposed by Ghiradella H (1989) J Morphol 202(1):69-88 and Saranathan V, et al. (2010) Proc Natl Acad Sci USA 107(26):11676-11681, where the two enantiomeric labyrinthine domains of the gyroid are connected to the extracellular and intra-SER spaces, our findings imply that the structural chirality of the single gyroid is, however, not caused by the molecular chirality of chitin. Furthermore, the wing scales are found to be highly textured, with a substantial fraction of domains exhibiting the <001> directions of the gyroid crystal aligned parallel to the scale surface normal. Both findings are needed to completely understand the photonic purpose of the single gyroid in gyroid-forming butterflies. More importantly, they show the level of control that morphogenesis exerts over secondary features of biological nanostructures, such as chirality or crystallographic texture, providing inspiration for biomimetic replication strategies for synthetic self-assembly mechanisms.

Inventory of butterfly fauna (Lepidoptera: Rhopalocera) of Tripura, India, in the Indo-Myanmar biogeographical zone, with records of threatened taxa

The Tripura province of northeast India, situated in the western fringe of the Indo-Myanmar biodiversity hotspot was extensively explored for butterfly fauna. We surveyed 28 wild and managed locations in the hot and humid environment of Tripura province (2009–2012) across different landscape gradients to observe and record butterfly diversity. We report here 212 butterfly species, 65 of which are considered threatened including 41 species protected by Indian Wildlife Protection Act 1972. Thirty-eight species are categorized as threatened by IUCN including one species also by CITES. We recorded the abundance of each butterfly species to highlight the population status of individual butterfly species in order to reveal the status of their conservation in Tripura, in India, and also at global scale. Geographic distribution of 142 species is extended to Tripura. Results of this study form a baseline data on the diversity and conservation of butterflies in this biodiversity hotspot.

Effect of postmortem aging on marination performance of broiler breast pectoralis major categorized by color lightness

The objective was to evaluate the effect of postmortem aging on marination performance of early-deboned chicken breast fillets (pectoralis major) with different color lightness. Effects of marination on muscle shear force were also determined. Early-deboned (2 h postmortem) broiler butterfly fillets were visually selected based on their color lightness (pale, normal, and dark) from a commercial plant. The individual butterfly fillets were separated into left and right fillets. One of them was used for 6-h marination treatment and the other for 24-h marination treatment. Samples were marinated in a vacuum tumbler (−0.6 atm, 16 rpm, 20 min) with 20% wt/wt marinade yielding 0.75% NaCl and 0.45% phosphate in the final product. The effect of aging on salt-induced water gain by breast muscle was also measured using the swelling/centrifuging method. Marinade uptake, marinade retention, raw product yield, and cooked product yield were determined after tumbling, following storage for 24 and 48 h after marination and after cooking. Salt-induced water gain was greater (P < 0.05) in nonmarinated fillets at 24 h postmortem compared with 6 h postmortem. Compared with unmarinated fillets, marination enhanced finished product yield significantly (P < 0.05) regardless of postmortem aging and color lightness. Marinade retention and product yield were different (P < 0.05) in fillets categorized by L* (lightness) values. There were no differences (P > 0.05) between 2 postmortem aging times for marinade uptake, overall product yield, cooking loss, final cooked product yield, or meat shear force regardless of initial fillet L* values. However, marinade retention of 6-h samples was significantly better than 24-h samples (P < 0.05). These results demonstrate that with a targeted 15% marinade uptake, postmortem aging of 2-h deboned fillets before marination does not affect marinade uptake and product yield, but significantly affects marinade retention by boneless skinless chicken breast.

Effects of Management Techniques on Grassland Butterfly Species Composition and Community Structure

Semi-natural grasslands are a crucial habitat for many butterfly species and the structure and extent of that grassland often dictates the composition of butterfly communities on the landscape. To understand effects on butterfly communities, we studied the impacts of different management schemes used to maintain semi-natural grasslands, including mowing every 3 y, mowing annually, and continuous summertime grazing. Transect count data were gathered over the 3 summers (2007–2009) in the Southern Appalachian Mountains of western Virginia and North Carolina. Eleven thousand two hundred and four butterfly individuals of 42 different species were documented over the course of the study. Fields with minimal management, being mowed only once every 3 y, had the largest benefit to butterfly communities. Species richness, abundance, and Shannon diversity was significantly higher in these fields. While abundance was not significantly different between annually mowed fields and grazed fields, mowed fields were significantly higher in richness and diversity. The analysis of habitat specialist species revealed minimally managed and mowed fields were higher in abundance and richness than grazed fields. The response of individual butterfly species also showed negative effects of grazing on habitat specialists. Overall, the results suggest a varying response by different groups of species as well as individual species, indicating multiple management techniques are necessary for conserving a wide range of species. Specific techniques can be used in conservation to target specialist groups of butterflies and rare species.

Identifying time lags in the restoration of grassland butterfly communities: A multi-site assessment

Although grasslands are crucial habitats for European butterflies, large-scale declines in quality and area have devastated many species. Grassland restoration can contribute to the recovery of butterfly populations, although there is a paucity of information on the long-term effects of management. Using eight UK data sets (9–21years), we investigate changes in restoration success for (1) arable reversion sites, were grassland was established on bare ground using seed mixtures, and (2) grassland enhancement sites, where degraded grasslands are restored by scrub removal followed by the re-instigation of cutting/grazing. We also assessed the importance of individual butterfly traits and ecological characteristics in determining colonisation times. Consistent increases in restoration success over time were seen for arable reversion sites, with the most rapid rates of increase in restoration success seen over the first 10years. For grasslands enhancement there were no consistent increases in restoration success over time. Butterfly colonisation times were fastest for species with widespread host plants or where host plants established well during restoration. Low mobility butterfly species took longer to colonise. We show that arable reversion is an effective tool for the management of butterfly communities. We suggest that as restoration takes time to achieve, its use as a mitigation tool against future environmental change (i.e. by decreasing isolation in fragmented landscapes) needs to take into account such time lags.

Species- and sex-specific adjustments of movement behavior to landscape heterogeneity in butterflies

Landscapes are often considered as islands of suitable habitat patches located in a hostile and homogeneous matrix. Variation in matrix quality, however, can be differently perceived by individuals, generating variation in movements related to external conditions (i.e., contrasted boundaries, corridors, or barriers) and/or individual phenotypes (i.e., sex or age). Accordingly,movements may differ both among species and among conspecific individuals of various age and/or sex. Here, we quantified sex-dependent and condition-dependent variations in orientation capacity, exploration behavior, and adjustment of flight speed to landscape heterogeneity in 2 related butterfly species (Boloria aquilonaris and B. eunomia). Using experimental cages, we assessed 1) individual butterfly’s ability to discriminate between habitat and matrices of different types and hence to orientate themselves towards their habitat, 2) individual butterfly’s ability to adapt their flight behavior to their local environment, and 3) their propensity to cross habitat–matrix boundaries. We showed the existence of species-specific orientation capacity, changes in exploration behavior according to local environment, and differences in behavior at habitat boundaries that are consistent between sexes. The adjustment of flight speed was also species-specific and varied in an opposite way between sexes. We explore how these differences might have arisen from adaptive responses to differences in the spatial configuration of habitats and in life-history traits, and we discuss how they can lead to differences in functional connectivity measurements.

Meta-analysis of survey data to assess trends of prairie butterflies in Minnesota, USA during 1979–2005

During 1993–1996, two teams (Schlicht, Swengels) surveyed the same Minnesota prairies, but without any coordination of sites, routes, methods, dates, and results between teams. In 27 instances, both teams surveyed the same site in the same year between 30 June and 18 July. For the 18 most frequently recorded species, abundance indices (individuals/h per site) significantly covaried between teams for 11 (61%) species, including 2/3 prairie specialists tested. No species significantly correlated negatively, 17/18 species had positive correlations, and the preponderance of positive correlations was significant. Swengel indices per hour (two surveyors; unlimited-width transect) averaged 2.42 times Schlicht indices (one surveyor; fixed-width transect). These results demonstrate that transect surveys by different teams at the same sites but not the same routes produce similar rankings of species abundance among sites. This approach to population monitoring (transect surveys during the season that covers the most specialist species at once, not necessarily with fixed routes but recording all species seen) might also be appropriate in other regions with high habitat loss and low human population density. Abundance indices from surveys by seven teams spanning 1979–2005 were calculated for evaluating population trends. For the five analyzable specialist species, 25/30 population trend tests of a species at a site had a negative direction, a highly significant skewing (P < 0.0001). By contrast, five “common” (most frequently recorded non-specialist) species had an even distribution of negative and positive trends. While adjacent sites had similarly timed decline thresholds (last year when a higher rate or any individual was recorded vs. first year when all subsequent indices were lower or zero) within species, these thresholds were not synchronized among sites in different counties. All sites analyzed in this study were preserves managed primarily with fire. While the ecosystem (or vegetative) approach to reserve selection has been validated in other studies to be effective at capturing populations of associated specialist butterflies, butterfly declines after reserve designation will likely continue unless the ecosystem approach to reserve management includes specific consideration of individual butterfly species’ required resources and management tolerances.

Butterfly responses to prairie restoration through fire and grazing

The development of land for modern agriculture has resulted in losses of native prairie habitat. The small, isolated patches of prairie habitat that remain are threatened by fire suppression, overgrazing, and invasion by non-native species. We evaluated the effects of three restoration practices (grazing only, burning only, and burning and grazing) on the vegetation characteristics and butterfly communities of remnant prairies. Total butterfly abundance was highest on prairies that were managed with burning and grazing and lowest on those that were only burned. Butterfly species richness did not differ among any of the restoration practices. Butterfly species diversity was highest on sites that were only burned. Responses of individual butterfly species to restoration practices were highly variable. In the best predictive regression model, total butterfly abundance was negatively associated with the percent cover of bare ground and positively associated with the percent cover of forbs. Canonical correspondence analysis revealed that sites with burned only and grazed only practices could be separated based on their butterfly community composition. Butterfly communities in each of the three restoration practices are equally species rich but different practices yield compositionally different butterfly communities. Because of this variation in butterfly species responses to different restoration practices, there is no single practice that will benefit all species or even all species within habitat-specialist or habitat-generalist habitat guilds.

Butterflies highlight the conservation value of hay meadows highly threatened by land-use changes in a protected Mediterranean area

Butterfly assemblages were used to characterize and evaluate the conservation value of the main habitat types in the Aiguamolls de l’Empordà Natural Park (north-eastern Spain), an important protected wetland area on the Mediterranean coast. Butterfly data were obtained from a number of transects walked as part of the Catalan Butterfly Monitoring Scheme, which uses a standardized methodology for monitoring butterflies. A Mantel test indicated a strong association between habitat types and the composition of butterfly assemblages and a principal component analysis ordinated individual butterfly species along a gradient from woodland to open areas, thereby indicating various degrees of shade tolerance. In addition, cluster analysis distinguished two main groups of habitats based on the similarities of their butterfly fauna: woodland and bramble clumps and a group of three different kinds of grasslands (traditionally hay meadows, pastures, and alfalfa fields). Hay meadows flooded in winter (the so-called closes) appeared always as the highest ranked habitat in terms of conservation evaluation: they have more butterflies and a slight tendency to harbor more and generally rarer species. This conclusion coincides with that of previous investigations that have indicated that the most diverse and rare plant communities in the whole Natural Park are present in the closes, and highlights the importance of traditionally managed hay meadows for wildlife. However, these hay meadows – one of the rarest habitats in the Mediterranean region – are in alarming decline and have become the most threatened habitat in this protected area: no longer profitable, we believe that the future of the closes will depend ultimately on the existence of agri-environmental schemes.

Smooth-billed ani ( Crotophaga ani ) predation on butterflies in Mato Grosso, Brazil: risk decreases with increased group size

Although most insects are vulnerable to predation by a variety of predators, including birds, there are few direct observational studies in the wild of avian predation on adult butterflies. We examined the predatory behavior of smooth-billed anis (Crotophaga ani) on butterflies, and the spacing behavior of the butterflies which were concentrated on a mineral-rich beach on the Cristalino River, in Mato Grosso, Brazil. We studied eight of the most regularly occurring butterfly species which came each morning to engage in "puddling." Most species of butterfly were closely associated with conspecifics, although nearest-neighbor distance varied among species. The pierids – "yellows" (Aphrissa statira, Phoebis trite), "oranges" (Phoebis argante), and sometimes "whites" (Daptoneura leucadia) – formed very dense groups (or clusters) of up to 1,000 individuals occasionally joined by a few kite swallowtails (Eurytides spp.). Most other butterfly species formed small groups (e.g., daggerwings, Marpesia spp.) or were dispersed individually and non-clumped over the beach (e.g., dingy purplewing, Eunica monima). Anis foraged using two strategies: rapid frontal attack on dense groups of butterflies (yellows, oranges, whites), and a stealthy approach to solitary butterflies (mainly purplewings) or those in small groups. For yellows, the most common butterfly caught by anis, the capture rate reached over 6 per 15 min per ani, and about 8% of those captured managed to escape. Capture rates were much lower for the other species. Time of day, age of the ani (adult or young-of-the-year), and total number of each butterfly species present accounted for variation in the number of each species captured by anis. The number of butterflies captured per 15 min increased as the number of butterflies present increased, but reached a threshold beyond which the capture rate did not increase. The capture rate per individual butterfly (individual risk) decreased with group size up to a group of 40 individuals and remained low with further increases. Thus a butterfly in a group of 100 was no less likely to be eaten than one in a group of 40. For individual ani forays into dense groups of pierids, an individual ani was unable to catch more than 16, regardless of group size. These data confirm the dilution effect of group size for butterflies; each individual yellow or orange was less at risk from ani predation when in a group.