Bill Length Research Articles

Patterns of postnatal growth in a small falcon, the lesser kestrel Falco naumanni (Fleischer, 1818) (Aves: Falconidae)

Following a dramatic decline, the lesser kestrel Falco naumanni global population has recently stabilised, although it is still fluctuating in several countries, including Greece. Nestling growth rates and size at fledging greatly influence future survival and reproductive success, and therefore the study of postnatal growth can aid the understanding of population dynamics and the conservation of avian populations. We quantified body mass and morphological traits in female and male lesser kestrel nestlings from a lowland Greek breeding population. Nonlinear mixed models were used to describe and compare growth trajectories. Growth in body mass, tarsus and bill reached asymptotic values before fledging and was best described by the logistic equation, whereas total length grew linearly beyond the fledging phase. Random variation was found in the asymptote in body mass, the inflection point in body mass, tarsus and bill lengths and the intercept in total length, being substantially higher between nests than amongst siblings, implying differences in parental quality between nests and also an even distribution of parental care amongst siblings. Random effects were not observed on the growth rate constant, supporting the hypothesis that it varies little within populations. Females were significantly heavier and had longer bills and total length than males, whereas males were similar to females in tarsus growth. Nonlinear mixed models allowed us to describe a stage of avian life vital for future survival and reproductive output and reveal variation between nests, nestlings and the sexes.

Natural epigenetic variation within and among six subspecies of the house sparrow, Passer domesticus.

Epigenetic modifications can respond rapidly to environmental changes and can shape phenotypic variation in accordance with environmental stimuli. One of the most studied epigenetic marks is DNA methylation. In the present study, we used the methylation-sensitive amplified polymorphism (MSAP) technique to investigate the natural variation in DNA methylation within and among subspecies of the house sparrow, Passer domesticus We focused on five subspecies from the Middle East because they show great variation in many ecological traits and because this region is the probable origin for the house sparrow's commensal relationship with humans. We analysed house sparrows from Spain as an outgroup. The level of variation in DNA methylation was similar among the five house sparrow subspecies from the Middle East despite high phenotypic and environmental variation, but the non-commensal subspecies was differentiated from the other four (commensal) Middle Eastern subspecies. Further, the European subspecies was differentiated from all other subspecies in DNA methylation. Our results indicate that variation in DNA methylation does not strictly follow subspecies designations. We detected a correlation between methylation level and some morphological traits, such as standardized bill length, and we suggest that part of the high morphological variation in the native populations of the house sparrow is influenced by differentially methylated regions in specific loci throughout the genome. We also detected 10 differentially methylated loci among subspecies and three loci that differentiated between commensal or non-commensal status. Therefore, the MSAP technique detected larger scale differences among the European and non-commensal subspecies, but did not detect finer scale differences among the other Middle Eastern subspecies.

Trait Evolution in Adaptive Radiations: Modeling and Measuring Interspecific Competition on Phylogenies.

The incorporation of ecological processes into models of trait evolution is important for understanding past drivers of evolutionary change. Species interactions have long been thought to be key drivers of trait evolution. However, models for comparative data that account for interactions between species are lacking. One of the challenges is that such models are intractable and difficult to express analytically. Here we present phylogenetic models of trait evolution that include interspecific competition among chosen species. Competition is modeled as a tendency of sympatric species to evolve toward difference from one another, producing trait overdispersion and high phylogenetic signal. The model predicts elevated trait variance across species and a slowdown in evolutionary rate both across the clade and within each branch. The model also predicts a reduction in correlation between otherwise correlated traits. We use an approximate Bayesian computation approach to estimate model parameters. We find reasonable power to detect competition in sufficiently large (20+ species) trees compared with Brownian trait evolution and with Ornstein-Uhlenbeck and early burst models. We apply the model to examine the evolution of bill morphology of Darwin's finches and find evidence that competition affects the evolution of bill length.

Biometrics and body masses of some birds of prey of Argentina

We present data from 97 live specimens from 20 different taxa of diurnal raptors from Argentina. Data were obtained from bird banding campaigns conducted by the Centro Nacional de Anillado de Aves (CENAA), Universidad Nacional de Tucuman, Argentina. Another important source of data was the Centro de Rehabilitacion de Aves Rapaces (CeRAR). We used mist nets and balchatri traps to catch birds during CENAA campaigns in central and northern Argentina, in order to band them and study their migration. During fieldwork, we measured total body length, bill length (exposed culmen and culmen with cere), wing chord, and body mass of each bird. The biometric information of raptors in Argentina is scarce. These measurements can therefore be useful for a variety of topics such as conservation, ecology, biology, taxonomy and phylogeny.

Age and seasonal differences in the biometrics of dunlins (Calidris alpina) migrating in spring through the Pripyat River floodplain, southern Belarus

Analysis of the biometric parameters of dunlins is based on data of 496 adult birds and 214 birds in their second year of life captured during the spring migration in the years 2002–2014 in the floodplain of the Pripyat River in southern Belarus. The average size of the dunlins caught in this area shows that the majority of birds correspond to the parameters of the nominate subspecies (C. a. alpina). We have not found any statistically significant differences between the age groups in all morphometric parameters except for the length of the wing, which in the birds in their second year of life is slightly smaller than in adults. Both the adult dunlins and the yearlings have two peaks in the distribution of biometric parameters, such as the bill length to the nostril, the bill length to the feathering, the total length of the head with the bill, and the length of the wing, which is associated with differences in the size of males and females. We have noted an increase in the average bill length to the nostril, bill to feathering length, and the total length of the head with the bill, as well as the wing length in the adult birds captured during the spring migration. These values are especially significant in the last five days of May. The body mass index of the dunlins passing through the floodplain of the Pripyat River increases intensively during the migration, which can partly be attributed to the later migration of large birds (females). However, the main reason for the increase in the body mass index is that the birds migrating later in spring have higher energy reserves compared with the earlier migrants. At the end of the migration period, in the floodplain of the Pripyat River, the body mass indices of dunlins are very high. This suggests that birds leaving the stopover site in southern Belarus in early June have sufficient energy resources to reach the nesting places in one nonstop flight.

Both natural selection and isolation by distance explain phenotypic divergence in bill size and body mass between South Australian little penguin colonies.

Morphological variation between populations of the same species can arise as a response to genetic variation, local environmental conditions, or a combination of both. In this study, I examined small‐scale geographic variation in bill size and body mass in little penguins (Eudyptula minor) across five breeding colonies in South Australia separated by <150 km. To help understand patterns driving the differences, I investigated these variations in relation to environmental parameters (air temperature, sea surface temperature, and water depth) and geographic distances between the colonies. I found substantial morphological variation among the colonies for body mass and bill measurements (except bill length). Colonies further located from each other showed greater morphological divergence overall than adjacent colonies. In addition, phenotypic traits were somewhat correlated to environmental parameters. Birds at colonies surrounded by hotter sea surface temperatures were heavier with longer and larger bills. Birds with larger and longer bills were also found at colonies surrounded by shallower waters. Overall, the results suggest that both environmental factors (natural selection) and interpopulation distances (isolation by distance) are causes of phenotypic differentiation between South Australian little penguin colonies.

Natural selection on morphology varies among years and by sex in Magellanic Penguins (Spheniscus magellanicus)

ABSTRACT The evolution of morphology in a population reflects several factors, including the influence of environmental variability on natural selection. We estimated natural selection on, and heritability of, 4 individual morphological traits (bill length, bill depth, flipper length, and foot length) and 2 multivariate morphological traits in adult Magellanic Penguins (Spheniscus magellanicus) at Punta Tombo, Argentina, from 1983 to 2010. We estimated heritability of morphology with parent–offspring regression and animal models, conditioning on sex because the species is sexually dimorphic. For the analysis of selection on each trait, we estimated both linear and quadratic selection gradients, based on the number of fledglings produced, for breeding males and females in each year. Estimates from animal models indicated that all 6 traits were heritable; in parent–offspring regressions, corresponding heritabilities were significantly higher in sons than in daughters in 100% of tests. Over 28 yr, we detecte...

Multivariate selection and intersexual genetic constraints in a wild bird population.

When selection differs between the sexes for traits that are genetically correlated between the sexes, there is potential for the effect of selection in one sex to be altered by indirect selection in the other sex, a situation commonly referred to as intralocus sexual conflict (ISC). While potentially common, ISC has rarely been studied in wild populations. Here, we studied ISC over a set of morphological traits (wing length, tarsus length, bill depth and bill length) in a wild population of great tits (Parus major) from Wytham Woods, UK. Specifically, we quantified the microevolutionary impacts of ISC by combining intra- and intersex additive genetic (co)variances and sex-specific selection estimates in a multivariate framework. Large genetic correlations between homologous male and female traits combined with evidence for sex-specific multivariate survival selection suggested that ISC could play an appreciable role in the evolution of this population. Together, multivariate sex-specific selection and additive genetic (co)variance for the traits considered accounted for additive genetic variance in fitness that was uncorrelated between the sexes (cross-sex genetic correlation=-0.003, 95% CI=-0.83, 0.83). Gender load, defined as the reduction in a population's rate of adaptation due to sex-specific effects, was estimated at 50% (95% CI=13%, 86%). This study provides novel insights into the evolution of sexual dimorphism in wild populations and illustrates how quantitative genetics and selection analyses can be combined in a multivariate framework to quantify the microevolutionary impacts of ISC.

Effects of hummingbird morphology on specialization in pollination networks vary with resource availability

Specialization of species in interaction networks influences network stability and ecosystem functioning. Spatial and temporal variation in resource availability may provide insight into how ecological factors, such as resource abundance, and evolutionary factors, such as phylogenetically conserved morphological traits, influence specialization within mutualistic networks. We used independent measures of hummingbird abundance and resources (nectar), information on hummingbird traits and plant–hummingbird interactions to examine how resource availability and species' morphology influence the specialization of hummingbirds in three habitat types (forest, shrubs, cattle ranch) sampled over 10 sessions across two years in the southern Andes of Ecuador. Specialization of hummingbird species in the networks was measured by three indices: d' (related to niche partitioning), generality (related to niche width) and PSI (related to pollination services). Specialization indices d', generality and PSI of hummingbird species were influenced by resource availability. All indices indicated that specialization of hummingbirds increased when the availability of resources decreased. Variation in d' was also explained by an interaction between resource availability and bill length; hummingbirds with a long bill switched from being more specialized than other species when resource availability was low to being similarly specialized when availability was high. Overall, our results highlight the importance of ecological and evolutionary factors determining the specialization of species in interaction networks. We demonstrate in particular that ecological gradients in resource availability cause substantial changes in consumers' foraging behavior contingent on their morphology. Changes in pollinator specialization along resource gradients can have impacts on ecosystem functions, such as pollination by animals.

Sex differences in growth rates of Yellow-legged Gull Larus michahellis chicks

ABSTRACTCapsule: Chick growth rates was sex-dependent in an Atlantic Yellow-legged Gull Larus michahellis population.Aims: To describe the growth rate of Yellow-legged Gull chicks and sex-associated variations, and obtain a discriminant function to sex them using morphological data.Methods: Fifty-two Yellow-legged Gull chicks from a colony in northern Iberia were measured for body mass, head and bill length, tarsus length and three other bill-length associated variables, from the hatching date up to the age of 36 days. Birds were sexed using DNA analysis.Results: Using logistic models, chick growth rates was observed to be similar between the sexes, while the asymptote was higher among males for the majority of the variables. Discriminant analyses showed that the variable head+bill was very reliable to predict the sex of >80% of chicks at an early developmental stage, and 100% of chicks if combined with tarsus length and two more bill-length associated variables at the age of 35 days.Conclusions: This is the first study using a discriminant analysis to sex Yellow-legged Gull chicks, and also the first to describe the growth function for the species. The growth rate varied between sexes because males showed higher asymptote values within the growth function.

Toxoplasma gondii Infection in Seagull Chicks Is Related to the Consumption of Freshwater Food Resources.

Understanding the spread of Toxoplasma gondii (T. gondii) in wild birds, particularly in those with opportunistic feeding behavior, is of interest for elucidating the epidemiological involvement of these birds in the maintenance and dissemination of the parasite. Overall, from 2009 to 2011, we collected sera from 525 seagull chicks (Yellow-legged gull (Larus michahellis) and Audouin’s gull (L. audouinii)) from 6 breeding colonies in Spain and tested them using the modified agglutination test (MAT) for the presence of antibodies against T. gondii. Chick age was estimated from bill length. Main food source of seagull chicks was evaluated using stable isotope analyses from growing scapular feathers. Overall T. gondii seroprevalence was 21.0% (IC95% 17.5–24.4). A generalized linear mixed-effects model indicated that year (2009) and food source (freshwater) were risk factors associated to the individual risk of infection by T. gondii, while age (days) was close to significance. Freshwater food origin was related to the highest seroprevalence levels, followed by marine origin, supporting freshwater and sewages as important routes of dispersion of T. gondii. Year differences could indicate fluctuating rates of exposure of seagull chicks to T. gondii. Age ranged from 4 to 30 days and seropositivity tended to increase with age (P = 0.07), supporting that seropositivity is related to T. gondii infection rather than to maternal transfer of antibodies, which in gulls is known to sharply decrease with chick age. This study is the first to report T. gondii antibodies in Yellow-legged and Audouin’s gulls, thereby extending the range of intermediate hosts for this parasite and underscoring the complexity of its epidemiology.

Sex-Based Differences in Adélie Penguin (Pygoscelis adeliae) Chick Growth Rates and Diet.

Sexually size-dimorphic species must show some difference between the sexes in growth rate and/or length of growing period. Such differences in growth parameters can cause the sexes to be impacted by environmental variability in different ways, and understanding these differences allows a better understanding of patterns in productivity between individuals and populations. We investigated differences in growth rate and diet between male and female Adélie Penguin (Pygoscelis adeliae) chicks during two breeding seasons at Cape Crozier, Ross Island, Antarctica. Adélie Penguins are a slightly dimorphic species, with adult males averaging larger than adult females in mass (~11%) as well as bill (~8%) and flipper length (~3%). We measured mass and length of flipper, bill, tibiotarsus, and foot at 5-day intervals for 45 male and 40 female individually-marked chicks. Chick sex was molecularly determined from feathers. We used linear mixed effects models to estimate daily growth rate as a function of chick sex, while controlling for hatching order, brood size, year, and potential variation in breeding quality between pairs of parents. Accounting for season and hatching order, male chicks gained mass an average of 15.6 g d-1 faster than females. Similarly, growth in bill length was faster for males, and the calculated bill size difference at fledging was similar to that observed in adults. There was no evidence for sex-based differences in growth of other morphological features. Adélie diet at Ross Island is composed almost entirely of two species—one krill (Euphausia crystallorophias) and one fish (Pleuragramma antarctica), with fish having a higher caloric value. Using isotopic analyses of feather samples, we also determined that male chicks were fed a higher proportion of fish than female chicks. The related differences in provisioning and growth rates of male and female offspring provides a greater understanding of the ways in which ecological factors may impact the two sexes differently.

Migration patterns of San Francisco Bay Area Hermit Thrushes differ across a fine spatial scale

AbstractEffective conservation of short-distance migrants requires an understanding of intraspecific variation in migratory patterns across small spatial scales. Until the advent of ultra-light geolocation devices, our knowledge of the migratory connectivity of songbirds was limited. For the Hermit Thrush (Catharus guttatus), subspecies delineations and connectivity patterns have been unclear in the portion of their breeding range in western North America from southeastern Alaska to northwestern Washington, where individuals wintering in the San Francisco Bay Area of California purportedly breed. To determine breeding locations and migratory timing of the Bay Area’s wintering Hermit Thrushes, we deployed geolocators at sites to the north and south of the San Francisco Bay. We compared results from these two regions to one another and to connectivity patterns suggested by subspecies definitions. We collected morphometrics to identify regional differences. Hermit Thrushes that wintered in the North Bay had a wider and more southerly breeding distribution from the British Columbia coast to northwestern Washington, whereas South Bay thrushes migrated to southeastern Alaska and the British Columbia coast. In general, North Bay thrushes departed wintering grounds and arrived on breeding grounds earlier than South Bay thrushes, but we cannot eliminate sex as a factor in these differences. Regional morphology differed only in bill length. Intraspecific isolation in glacial refugia during the Late Pleistocene may explain these fine-scale geographic variations in migration patterns and morphology.

The dual role of Andean topography in primary divergence: functional and neutral variation among populations of the hummingbird, Metallura tyrianthina.

BackgroundThe ridges and valleys of the Andes create physical barriers that limit animal dispersal and cause deterministic local variation in rainfall. This has resulted in physical isolation of animal populations and variation in habitats, each of which has likely contributed to the evolution of high species diversity in the region. However, the relative influences of geographic isolation, ecoclimatic conditions, and their potential interactions remain poorly understood. To address this, we compared patterns of genetic and morphological diversity in Peruvian populations of the hummingbird Metallura tyrianthina.ResultsPhylogenetic and variation partitioning analyses showed that geographic isolation rather than climatic dissimilarity explained the greatest proportion of genetic variance. In contrast, bill length variation was explained by climatic seasonality, but not by genetic divergence. We found that mutation-scaled migration rate (m) between persistently humid and semi-humid environments was nearly 20 times higher when the habitats were contiguous (m = 39.9) than when separated by a barrier, the Cordillera de Vilcanota (m = 2.1). Moreover, the population experiencing more gene flow exhibited a lesser degree of bill length divergence despite similar differences in climate.ConclusionsGeographic isolation is necessary for genetic divergence. Ecological differences, represented here by climate characteristics, are necessary for functional divergence. Gene flow appears to hinder the evolution of functional traits toward local adaptive optima. This suggests that functional diversification requires geographic isolation followed or accompanied by a shift in ecological conditions. Andean topography causes both isolation and climatic variation, underscoring its dual role in biotic diversification.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-016-0595-2) contains supplementary material, which is available to authorized users.

Multiple Reversals of Bill Length over 1.7 Million Years in a Hawaiian Bird Lineage.

Evolutionary change has been documented over geological time, but reversals in morphology, from an ancestral state to a derived state and back again, tend to be rare. Multiple reversals along the same lineage are even rarer. We use the chronology of the Hawaiian Islands and an avian example, the Hawaiian honeycreeper 'amakihi (Hemignathus spp.) lineage, which originated on the oldest main island of Kaua'i 1.7 million years ago, to examine the process of sequential reversals in bill length. We document three single and two multiple reversals of bill length on six main islands from oldest to youngest, consistent with the phylogeny of the lineage. Longer bills occur on islands with endemic species, including phylogenetically relevant outgroups, that may compete with or dominate the 'amakihi. On islands without those species, the 'amakihi had shorter bills of similar length. Both types of reversals in morphology in this lineage integrate microevolutionary processes with macroevolution in the adaptive radiation of Hawaiian honeycreepers.

Morphological differentiation of Icelandic Redpolls, Acanthis flammea islandica

Capsule The analyses support the grouping of the three Acanthis species, although a large split is observed between the A. hornemanni subspecies.Aims To investigate the morphological variation in A. f. islandica among different periods of the year and its morphological differentiation from the other subspecies A. f. flammea and A. f. rostrata, and also from the redpoll species, A. cabaret and the two subspecies of A. hornemanni, exilipes and hornemanni.Methods The subspecies status of the Icelandic population was evaluated with Amadon's rule, by comparing its variation of traits to the distribution of the traits in different species/subspecies of the group.Results A. f. islandica is characterized by intermediate wing, bill and tail lengths. Based on the 75% rule, wing length and bill depth can be used to discriminate A. f. islandica from both extreme morphs of redpolls (currently classified as different species); A. hornemanni and A. cabaret, and tail and wing length can distinguish A. f. islandica from its conspecifics A. f. flammea. The overall morphological divergence within the redpoll complex is not supported by association to the studied nuclear markers.Conclusion The taxonomic status of the three redpoll species is supported by Amadon's rule, however the subspecies status of the Icelandic Redpoll remains unclear.

Differentiating Sex and Species of Western Grebes (Aechmophorus occidentalis) and Clark's Grebes (Aechmophorus clarkii) and Their Eggs Using External Morphometrics and Discriminant Function Analysis

Abstract. In birds where males and females are similar in size and plumage, sex determination by alternative means is necessary. Discriminant function analysis based on external morphometrics was used to distinguish males from females in two closely related species: Western Grebe (Aechmophorus occidentalis) and Clark's Grebe (A. clarkii). Additionally, discriminant function analysis was used to evaluate morphometric divergence between Western and Clark's grebe adults and eggs. Aechmophorus grebe adults (n = 576) and eggs (n = 130) were sampled across 29 lakes and reservoirs throughout California, USA, and adult sex was determined using molecular analysis. Both Western and Clark's grebes exhibited considerable sexual size dimorphism. Males averaged 6–26% larger than females among seven morphological measurements, with the greatest sexual size dimorphism occurring for bill morphometrics. Discriminant functions based on bill length, bill depth, and short tarsus length correctly assigned sex to 98% of Western...

Sex determination of African Penguins Spheniscus demersus using bill measurements: method comparisons and implications for use

African Penguins Spheniscus demersus are sexually dimorphic; on average, males are larger than females but measurements overlap making sex determination difficult through observations alone. We developed a discriminant function, using bill length and depth from a sample of birds sexed from gonad visualisation during post-mortem, which correctly classified 93% of the individuals. Cross-validation correctly assigned 90% of DNA-sexed birds and 91% of birds sexed by partner measurement comparisons. The use of discriminant function score cutpoints, while leaving 16% and 29% of birds unclassified, improved accuracy of birds sexed by DNA to 97% and of those sexed by partner comparison to 99%. Bill depth was found to be a discriminating variable. However, two techniques for measuring bill depth are currently in use for African Penguins. While these measurements are correlated (r = 0.85), they differ on average by 1.4 mm hindering accuracy of sex determination when using a discriminant function developed from the other bill depth measurement. Exploration of adult bill morphology of birds sexed from DNA at different colonies suggests the discriminant functions can be applied throughout the African Penguins’ South African range.

Phenotypic characterization and production potentials of Nageswari duck in Bangladesh

The present study was conducted to know the morphology, morphometry, production and reproduction potentialities of Nageswari duck, an indigenous duck genetic resource of Bangladesh. Data on 58 representative adult Nageswari ducks were included for morphological study from 24 duck owners and two government organizations having Nageswari duck flocks while 468 individuals were considered for the traits of productive and reproductive performances. Information was collected by using a structured questionnaire through personal interaction, on spot recording and direct phenotypic measurements in five different regions of Bangladesh. Black plumage color with white stripe extended from neck to breast make unique features of Nageswari duck compared to other indigenous ducks. Morphometric measurements on adult live weight, body length, head diameter, bill length, neck length, shank length, wing length, massiveness and condition index in male and female were found to be 1.66±0.07 and 1.51±0.05 kg, 26.27±0.57 and 23.79±0.39 cm, 3.49±0.02 and 3.36±0.04 cm, 5.87±0.09 and 5.54±0.07 cm, 23.49±0.58 and 21.59±0.49 cm, 5.76±0.12 and 5.16±0.11 cm, 24.58±0.49 and 21.99±0.53 cm, 6.33±0.28 and 6.39±0.22, and 6.72±0.23 and 6.93±0.23 respectively. Age at first egg of Nageswari duck was found to be 168.48±3.53 days. Total number of eggs laid per year averaged 173.63±3.39 and peak production was found in 29.46±0.19 weeks. The average egg weight was estimated to be 67.32±0.82 g and characteristic bluish tinge of egg color was observed. Breed specific characteristic features and production profiles were observed in this study. The present study provided some baseline information on Nageswari duck of Bangladesh which could be useful for genetic characterization, conservation and future improvement programs in Bangladesh.Bang. J. Anim. Sci. 2015. 44(2): 92-99

Morphological classification of conspecific birds from closely situated breeding areas – A case study of the Common Nightingale

Abstract In this paper, a complex morphological comparison of four Common Nightingale groups (Luscinia megarhynchos) is demonstrated. In total, 121 territorial nightingales were mist-netted and measured individually on four study areas called ‘Bódva’, ‘Felső-Tisza’, ‘Szatmár-Bereg’ and ‘Bátorliget’ in the North-Eastern part of Hungary in 2006–2013. To distinguish groups by morphology, Classification and Regression Trees (CART), Random Forest (RF) and Linear Discriminant Analysis (LDA) methods were used. Comparison of the four studied Common Nightingale groups shows substantial morphological differences in the length of the second, the third and the fourth primaries (P2, P3, P4), in bill length (BL) and bill width (BW), while other characteristics showed greater similarities. Based on the results of all the applied classification methods, birds originated from Szatmár-Bereg were clearly distinguishable from the others. The differences in morphology can be explained by interspecific competition or phenotypic plasticity resulting from the change of ecological, environmental parameters. Our case study highlights the advantageous differences of the classification methods to distinguish groups with similar morphology and to choose important variables for classification. In conclusion, broad application of the classification methods RF and CART is highly recommended in comparative ecological studies.