When considering smaller scale UAV’s there is not a lot available that could survey large areas quickly, stealthy, and with a considerable range. Owls have an interesting trait that is not found in most avian species; leading-edge serrations. These serrations give owls the ability to fly silently and steadily without sacrificing maneuverability. The focus of the research was to design leading-edge serrations that would improve the flight performance of a Styrofoam glider. Previous studies defined serrations by the inclination angle, tip-displacement angle, and the length of the serration in the x-y plane. Using these parameters, a serration mold was computer modeled and 3D printed from a resin material. Silicone was used to cast the mold, allowing flexible serrations to be created. The serrations were fitted onto the leading-edge of a Styrofoam glider which was used for flight testing. Flight test between serrated and non-serrated leading-edge gliders are presented and compared.

This thesis aims to investigate and reduce the aerodynamic noise source known as trailing edge noise, or airfoil self-noise, by using passive flow control techniques. Airfoil self-noise is produced when a turbulent boundary layer generated on an airfoil surface is scattered by the airfoil’s trailing edge. The investigation is of experimental nature, conducted in the aeroacoustic as well as aerodynamic wind tunnel facilities at Brunel University London and the Institute of Sound and Vibration (ISVR) at the University of Southampton. The research is relevant for any application in which airfoil blades encounter a smooth non-turbulent inflow and hence where trailing edge noise is a dominant noise source. Potential applications can therefore be fan or rotor blades in aero-engines, wind turbine blades or industrial cooling fans. The approach taken for the reduction of trailing edge noise utilises passive flow control techniques through the use of trailing edge serrations and the additional support of porous materials. Both of the aforementioned are inspired by the owl’s silent flight due to its unique wing structure. The research presented here can be divided in three parts: The first part comprises an extensive assessment of the performance of non-flat plate trailing edge serrations for airfoil broadband noise and their aerodynamic performance in terms of lift and drag. It is found that serrations can realistically achieve noteworthy broadband airfoil self-noise reductions, however due to the fact that non-flat plate serrations are directly cut into the airfoil body, the blunt sections in the serration root produce an additional noise source of vortex shedding tonal noise. The second part investigates the two flow mechanisms involved. Regarding the mechanism responsible for broadband noise and the subsequent reductions by the serration geometry, the turbulent boundary layer structures are studied in depth on a serrated trailing edge of a flat plate. Experimental techniques such as hot wire anemometry, liquid crystal flow visualisation, unsteady surface pressure measurements and noise measurements are used. A redistribution of the momentum and turbulent energy near the sawtooth tip and side edges appears to reduce the trailing edge noise scattering-efficiency of the hydrodynamic pressure waves. For the study of the flow mechanism responsible for the vortex shedding tonal noise increase, noise and velocity measurements along with flow visualisation techniques are used for the identification and further understanding of this noise source. A highly three-dimensional wake-flow could be identified in the wake past the serration gap, which differs from the longitudinal vortices shed from a straight blunt serration root. The third part presents the concept of poro-serrated trailing edges as a novel method to substantially improve the overall noise performance of the non-flat plate trailing edge serration type. The use of porous metal foams or thin brush bundles which fill the interstices between adjacent members of the sawtooth can completely suppress the bluntness-induced vortex shedding noise. Most importantly a turbulent broadband noise reduction of up to 7 dB can be achieved without compromising the aerodynamic performances in lift and drag. The new serrated trailing edges do not cause any noise increase throughout the frequency range investigated here. Through noise and velocity measurements near the trailing edge of an airfoil, the reduction of the broadband noise is found to be primarily caused by the sawtooth geometry. The new serrated trailing edges have the potential to improve the industrial worthiness of the serration technology in achieving low noise radiation.

Trailing edge noise is a common noise source in aerodynamic applications, such as wind turbines, duct fan blades, and propellers. As sound is a nuisance for people near this machinery, methods of reducing trailing edge noise are being investigated. A proven method of trailing edge noise reduction is using a serrated trailing edge. Many prior experiments have shown that a trailing edge with sawtooth serrations can reduce trailing edge noise compared to a straight trailing edge, but the mechanism by which sawtooth serrations reduce noise is not fully understood. Previous theoretical models have assumed that the turbulence field convecting past a serrated trailing edge is unchanged by the presence of the serrations, but experiments have shown that this is not the case in reality. This work attempts to further explore the mechanisms behind why trailing edge serrations reduce trailing edge noise. Additionally, it evaluates the usefulness of a wall jet wind tunnel for use in the study of serrated trailing edges. Experiments were conducted in an anechoic wall jet wind tunnel using a straight trailing edge configuration and a serrated trailing edge configuration. It was found that there may be differences in the unsteady surface pressure over serrated edges in one-sided flows as compared to two-sided flows, like on that of an airfoil, most notably in relation to the magnitude of the unsteady pressure on the serrations. In the wall jet and in agreement with other studies, it was found that the unsteady pressure fluctuations increase towards the tip of the serration in one-sided flows. This is counter to what is found in some studies of two-sided flows. Good agreement was found between some models of the wavenumber-frequency wall pressure spectrum of a turbulent boundary layer and the measured wall pressure spectrum on the straight trailing edge, and these models also produced good predictions of the noise produced by this trailing edge using Amiet's equation. A surface pressure microphone array was used to estimate the zero spanwise wavenumber surface pressure spectrum. This spectrum was used in Amiet's method to predict the measured trailing edge noise. Predictions using the wavenumber-filtered measurement tended to overpredict the measured far field noise most likely due to the inclusion of broader wavenumber content through the array's side lobe response and the breadth of the main lobe. The serrated trailing edge was found to increase coherence between two points on the same serration while reducing coherence between two points on different serrations. It was concluded that the presence of the serrations decorrelates small-scale turbulent eddies. Additionally, it was found that while the serrated trailing edge did reduce the noise produced, its destructive effect on the geometry-based resonance of the straight trailing edge configuration may have amplified the magnitude of the reduction. Finally, it was concluded that the serrations do indeed affect the hydrodynamic field near the trailing edge, and the theoretical models which make the assumption otherwise must be refined. / Master of Science / Trailing edge noise is a common noise source in aerodynamic applications, such as wind turbines, duct fan blades, and propellers. As sound is a nuisance for people near this machinery, methods of reducing trailing edge noise are being investigated. A proven method of trailing edge noise reduction is using a serrated trailing edge. Many prior experiments have shown that a trailing edge with sawtooth serrations can reduce trailing edge noise compared to a straight trailing edge, but the mechanism by which sawtooth serrations reduce noise is not fully understood. This work attempts to further explore the mechanisms behind why trailing edge serrations reduce noise. Experiments were conducted in an anechoic wind tunnel facility. It was found that a one-sided flow over a serrated trailing edge may be significantly different from that over a two-sided flow. Good agreement was found between prediction models and measurements of trailing edge noise. The serrated trailing edge was effective at reducing the coherence of turbulent eddies across the roots of the sawtooth serrations. It was concluded that the serrated trailing edge is effective at reducing noise, and that one means of doing so is decreasing the correlation of small-scale turbulent eddies, and that current models of the flow over serrations may need to be refined.

In this study, the teeth of the Carcharodon carcharias (Great White) and the Galeocerdo cuvier (Tiger) sharks were analyzed to examine their optimized structure-property relationships and edge serrations with regards to shearing. Structure-property analysis was conducted using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy, X-ray diffraction, and optical microscopy to study the teeth using parametric optimization. Quantifying the structural properties also focused on the tooth serrations, which were captured in SEM and micrographs and were analyzed for geometric parameters using ImageJ software. Nanoindentation was performed to determine the material's mechanical properties. Further, finite element analysis (FEA) of the sharks' teeth serrations were carried out to quantify the optimum shearing performance of each serration type – zeroth (no serrations), first (a single array of serrations), and second (a secondary array of serrations upon the first array) order serration. Here, serration order, bite velocity, and angle-of-impact for ascertaining sharks' teeth shearing performance were analyzed. FEA results showed that serrated edges reduced the energy required to pierce and shear materials as the angle of penetration moved away from perpendicular to the surface. These bioinspired findings will help advance the design and optimization of engineered cutting tools.

Plankerbverzahnungen zählen zu den Vertretern der Kupplungsverzahnungen, mit deren Hilfe zwei Bauteile koaxial miteinander verbunden werden können. Neben einer hohen Winkelgenauigkeit zeichnen sie sich durch eine enorme Drehmomentkapazität bei gleichzeitig geringem Montageaufwand aus. Die zur Leistungsübertragung erforderliche Vorspannkraft kann über eine zentrale Spannschraube oder mehrere dezentral, auf einem gemeinsamen Teilkreis, angeordnete Spannschrauben erzeugt werden. Diese Arbeit liefert einen Beitrag zur beanspruchungsgerechten Dimensionierung von Plankerbverzahnungen mit zentraler und dezentraler Verschraubung. Es wird eine Berechnungsmethode zur Bestimmung der Tragfähigkeit des Zahnfußes, der Zahnflanke und der Spannschrauben vorgestellt und anhand von Beispielrechnungen erläutert. Neben den umfangreichen theoretischen Betrachtungen werden die Ergebnisse zahlreicher experimenteller Untersuchungen präsentiert. Diese dienen der Gewinnung von grundlegenden Aussagen zur Stützwirkung und zum Mittelspannungseinfluss an einfach und mehrfach gekerbten Proben sowie zur Verifizierung des Tragfähigkeitsnachweises.

Three methods were developed to better understand and characterize the near-field dynamic processes of rotary bell atomization. The methods were developed with the goal of possible integration into industry to identify equipment changes through changes in the primary atomization of the bell. The first technique utilized high-speed imaging to capture qualitative ligament breakup and, in combination with a developed image processing technique and PIV software, was able to gain statistical size and velocity information about both ligaments and droplets in the image data. A second technique, using an Nd:YAG laser with an optical filter, was used to capture size statistics at even higher rotational speeds than the first technique, and was utilized to find differences between serrated and unserrated bell ligament and droplet data. The final technique was incorporating proper orthogonal decomposition (POD) into image data of a side-profile view of a damaged and undamaged bell during operation. This was done to capture differences between the data sets to come up with a characterization for identifying if a bell is damaged or not for future industrial integration.

Plankerbverzahnungen zählen zu den Vertretern der Kupplungsverzahnungen, mit deren Hilfe zwei Bauteile koaxial miteinander verbunden werden können. Neben einer hohen Winkelgenauigkeit zeichnen sie sich durch eine enorme Drehmomentkapazität bei gleichzeitig geringem Montageaufwand aus. Die zur Leistungsübertragung erforderliche Vorspannkraft kann über eine zentrale Spannschraube oder mehrere dezentral, auf einem gemeinsamen Teilkreis, angeordnete Spannschrauben erzeugt werden. Diese Arbeit liefert einen Beitrag zur beanspruchungsgerechten Dimensionierung von Plankerbverzahnungen mit zentraler und dezentraler Verschraubung. Es wird eine Berechnungsmethode zur Bestimmung der Tragfähigkeit des Zahnfußes, der Zahnflanke und der Spannschrauben vorgestellt und anhand von Beispielrechnungen erläutert. Neben den umfangreichen theoretischen Betrachtungen werden die Ergebnisse zahlreicher experimenteller Untersuchungen präsentiert. Diese dienen der Gewinnung von grundlegenden Aussagen zur Stützwirkung und zum Mittelspannungseinfluss an einfach und mehrfach gekerbten Proben sowie zur Verifizierung des Tragfähigkeitsnachweises.

We reviewed the taxonomy of the Trogon rufus species-complex under the premises of the Biological Species Concept. Putative taxonomic units, breaks and transition zones, were visualised by heatmaps and isophenes (phenotypic contour lines) of the colour, barring, morphometric and song characters and tested by discriminant function analyses. Colourmetric data were obtained via spectrometry and barring patterns analysed via high quality digital photographs. We found four distinct biological species. Trogon chrysochloros Pelzeln 1856 from the Atlantic Forest with its denser and blacker undertail and wing covert barring, larger size and faster, generally higher song with more notes. Its upperparts vary from bluer to more coppery-green with increasing altitude. The bill is also relatively smaller and more serrated, linked to a diet that consists almost exclusively of large arthropods, making it the most insectivorous new world Trogon species yet known, which may account for its relative rarity compared to other Trogonids with which it is sympatric. Trogon tenellus Cabanis 1862, from Central America, and Trogon cupreicauda Chapman 1914 from the Chocó-Magdalena provide a classic case of typical biological species, coming into contact in the extreme NW Chocó Province, Colombia, but without intermediate forms. T. tenellus is identified by its blue to blue-green uppertail, blue or grey eye-rings, grey tarsi and song with 2-4 notes, longer note duration and greater change in peak and high frequencies between the intro note and loudsong. This contrasts with the shiny olive-green to coppery green uppertails, yellow eye-ring, usually olive tarsi, brown wash on the undertail of females and song with 6-8 notes of shorter duration and little change in frequency between the intro note and loudsong of T. cupreicauda. T. cupreicauda varies clinally from generally bluer- to more coppery-green plumage and from thicker to thinner black bars in a gradient from the Pacific coast on the border with Ecuador to the Magdalena Valley. The greater difference in colour and barring relative to T. tenellus in the region they come into contact provides possible evidence of character displacement as a result of the competitive exclusion between these two species, maintaining their parapatric distributions. The Amazonian population belongs to a single species, Trogon rufus Gmelin 1788, but with two highly distinct forms that we designate as Trogon rufus rufus in the Guiana Shield and Trogon rufus sulphureus in S & W Amazonia, for which Todd\'s amazonicus is synonymised. They are morphologically and, to a lesser extent, vocally distinct across the lower Rio Negro and matrix of highland and open habitats of the Rio Branco basin but show limited character exchange between the 52-58th parallels west on the southern bank of the Amazon, centred around the Rio Arapiuns on the left bank of mouth of the Tapajos. We postulate that this is the result of secondary contact as a consequence of shifts in the course of the main channel of the Amazon River at times of lower sea levels during the Plio-Pleistocene. T .r. sulphureus is identified by a typically coppery uppertail with subterminal tailband of greener hue, yellow eye-ring, low barring density and broad black bars of the undertail and wing-coverts barring with and lack of a pectoral band. They are also sometimes distinguishable in song by a higher frequency introduction note and/or more pronounced descending modulation across the loudsong. This varies clinally on a west-east gradient, from strong-coppery to shiny olive-green uppertails with more to less distinct subterminal tailbands, diminishing black bar widths with corresponding increasing density and decreasing intro note low frequency. T. r. rufus have green uppertails, blue eye-rings, presence or absence of a white pectoral band and denser undertail and wing panel barring with thinner black bars. These characters were shown to change as a function of geographic distance between specimens of sulphureus and rufus, connected via the \'Arapiuns contact zone\', suggesting isolation by distance. This is reminiscent of a ring species pattern and two specimens with a possible mixture of characters were indeed found from the upper Rio Negro and in Pantepui, where T. r. rufus and T. r. sulphureus would be expected to come into contact, effectively \'closing the ring\'. Whether Trogon rufus constitutes a valid ring species requires further testing, preferably including molecular characters, but this clearly illustrates that the distinction between clinal variation and ring-species is a matter of degree, not kind, with the formation of the ring-species necessarily passing through a clinal stage with no overlap between terminal taxa. We therefore propose the concept of a loop species, where the terminal forms do not overlap but are connected via a series of intergrading populations. It seems likely that such patterns are more widespread in Amazonia than presently known due to the propensity for clinal variation and parapatric speciation lended by its massive geographical extent and abundance of biogeographical semi-permeable barriers. With regards to the population from the Pernambuco Center of Endemism, the few records suggest that it is a valid taxonomic unit. It has the unique combination of a song very similar to T. r. sulphureus due to the high introduction note frequency and pronounced descent in frequencies across the loudsong, with a corresponding widening range but moderately large size, serrated bill and blue eye-ring but this certainly requires confirmation. This requires urgent attention, as the remnant population is very small and localised, recorded only from the Murici municipality, Alagoas. / Nós revisamos a taxonomia do complexo Trogon rufus sob o conceito Biológico de Espécies. Unidades taxonômicas possíveis, quebras e zonas de transição taxonômicas foram definidas usando mapas de calor e isofenas (linhas de contorno de fenótípo) baseados em caráteres de cor, barramento e morfometria. Esses possíveis táxons foram testados pelas análises de discriminantes. Dados de coloração foram obtidos por meio de espectrometria, e os padrões de barramento por meio de fotos de alta qualidade. Nós encontramos quatro espécies biológicas distintas Trogon chrysochloros Pelzeln 1856, da Mata Atlântica, diagnosticável pelo barramento mais escuro e denso na face inferior da cauda e coberteiras da asa, maior tamanho corpóreo, canto mais rápido, com mais notas e de frequência mais alta. Suas partes superiores (cabeça, dorso e cauda) variam de azul a verde acobreado com o aumento da altitude. O bico também é relativamente menor e mais serrilhado, o que está ligado a uma dieta que consiste quase exclusivamente de grandes artrópodes, fazendo desta espécie o Trogon mais insetívoro do mundo, o que deve ser a razão de sua relativa raridade quando comparado a outros Trogonidae com os quais vive em simpatia. Trogon tenellus Cabanis 1862, da América Central, e Trogon cupreicauda Chapman 1914, do Chocó-Magdalena, formam um caso clássico de espécies biológicas, entrando em contato no extremo noroeste da província de Chocó, na Colômbia, sem a presença de formas intermediárias. T. tenellus é identificável pela face superior da cauda azul ou azul esverdeado, anel perioftálmico azul ou cinza, tarso cinza, e voz com de 2 a 4 notas, maior duração das notas e maior mudança entre frequência de pico e frequência alta entre a nota introdutória e nota principal. Essas características contrastam com a cor verde-oliva brilhante da face superior da cauda, anel perioftámico amarelo, tarso geralmente oliva, presença de marrom claro na face inferior da cauda das fêmeas e canto com entre 6 e 8 notas, de menor duração, pouca mudança na frequência entre a primeira nota e o canto principal de T. cupreicauda. Este varia clinalmente de azul para uma plumagem mais verde acobreada e de barramento preto mais espesso para mais fino em uma gradiente da costa do Pacífico, do noroeste do Equador até o Vale do Magdalena. A maior distinção de estados de caráter relativa a T. tenellus na região onde os dois grupos se encontram provê uma possível evidência de deslocamento de caracteres como resultado de exclusão competitiva entre estas duas espécies, mantendo suas distribuições parapátricas. A população amazônica pertence a única espécie biológica Trogon rufus Gmelin 1788, mas com duas formas altamente distintas que designamos como Trogon rufus rufus do Escudo Guianense, e Trogon rufus sulphureus no sul e oeste da Amazônia, com a qual amazonicus de Todd é sinonimizada. Estas são morfologicamente, e em menor escala, vocalmente distintas nas duas margens do baixo Rio Negro e áreas abertas e/ou montanhosas da bacia do Rio Branco, mas apresentam troca de caracteres limitada nas longitudes entre 52 e 58 Oeste na margem sul do Rio Amazonas, centrado nos arredores do Rio Arapiuns, na margem esquerda da foz do Tapajós. Nós postulamos que isto é um resultado de contato secundário, como consequência de mudanças no curso principal do Rio Amazonas em tempos de níveis mais baixos do mar durante o Plio-Pleistoceno. T. r. sulphureus é identificado pela coloração tipicamente acobreada da face superior da cauda com uma banda sub-terminal de tonalidade esverdeada, anel perioftálmico amarelo, barras negras espessas e de baixa densidade na face inferior da cauda e nas coberteiras das asas e pela ausência de uma faixa peitoral. Em certos casos eles também podem ser distinguíveis pela voz com uma nota introdutória de maior frequência e/ou uma modulação descendente mais pronunciada no canto principal. Este grupo varia clinalmente em gradiente de oeste para leste, de uma coloração cobre forte até verde oliva na face superior da cauda com faixa sub-terminal mais ou menos distinta, anel perioftálmico azul, presença ou ausência de uma faixa peitoral branca e barramento na face inferior da cauda e coberteiras de menor espessura e, consequentemente, maior densidade. Nossos dados apontam que estes caracteres mudam linearmente entre sulphureus e rufus de acordo com a distância ao longo de uma gradiente clinal em forma de laço do Oeste Amazônico até o Escudo das Guianas, conectado pela zona de contato de Arapiuns, sugerindo isolamento por distância. Isto sugere um remanescente de um padrão de espécie em anel. Além disso, dois espécimes com possível mistura de caracteres foram de fato encontrados no alto Rio Negro e Pantepui, onde se espera que T. r. rufus e T. r. sulphureus entrem em contato, fechando o anel efetivamente. Ainda é necessário testar se Trogon rufus constitui uma espécie em anel válida, preferencialmente usando dados moleculares, mas este caso ilustra claramente que a distinção entre variação clinal e espécie em anel é uma questão de grau e não de tipo, com a formação de espécie em anel necessariamente passando por um estágio clinal sem sobreposição entre os grupos terminais. Nós assim sugerimos o conceito de espécie em laço, onde as formas terminais não se sobrepõem, mas são ligadas através de uma série de populações onde há fluxo gênico. Parece provável que estes padrões são mais amplamente distribuídos na Amazônia do que é sabido atualmente devido a uma propensão à variação clinal e especiação parapátrica causada por sua grande extensão geográfica e abundância de barreiras geográficas semipermeáveis. Em relação a população do Centro de Endemismo Pernambuco, os poucos registros sugerem que esta é uma unidade taxonômica válida. Este grupo apresenta uma combinação única de canto muito similar ao de T. r. sulphureus, devido à alta frequência da nota introdutória e pronunciada modulação descendente ao longo do canto principal, com uma maior amplitude da frequência, combinada a maior tamanho, bico serrilhado, e anel perioftálmico azul, mas isso requer confirmação. Este caso demanda atenção urgente, já que a população remanescente é muito pequena e de distribuição restrita ao município de Murici, em Alagoas.

We reviewed the taxonomy of the Trogon rufus species-complex under the premises of the Biological Species Concept. Putative taxonomic units, breaks and transition zones, were visualised by heatmaps and isophenes (phenotypic contour lines) of the colour, barring, morphometric and song characters and tested by discriminant function analyses. Colourmetric data were obtained via spectrometry and barring patterns analysed via high quality digital photographs. We found four distinct biological species. Trogon chrysochloros Pelzeln 1856 from the Atlantic Forest with its denser and blacker undertail and wing covert barring, larger size and faster, generally higher song with more notes. Its upperparts vary from bluer to more coppery-green with increasing altitude. The bill is also relatively smaller and more serrated, linked to a diet that consists almost exclusively of large arthropods, making it the most insectivorous new world Trogon species yet known, which may account for its relative rarity compared to other Trogonids with which it is sympatric. Trogon tenellus Cabanis 1862, from Central America, and Trogon cupreicauda Chapman 1914 from the Chocó-Magdalena provide a classic case of typical biological species, coming into contact in the extreme NW Chocó Province, Colombia, but without intermediate forms. T. tenellus is identified by its blue to blue-green uppertail, blue or grey eye-rings, grey tarsi and song with 2-4 notes, longer note duration and greater change in peak and high frequencies between the intro note and loudsong. This contrasts with the shiny olive-green to coppery green uppertails, yellow eye-ring, usually olive tarsi, brown wash on the undertail of females and song with 6-8 notes of shorter duration and little change in frequency between the intro note and loudsong of T. cupreicauda. T. cupreicauda varies clinally from generally bluer- to more coppery-green plumage and from thicker to thinner black bars in a gradient from the Pacific coast on the border with Ecuador to the Magdalena Valley. The greater difference in colour and barring relative to T. tenellus in the region they come into contact provides possible evidence of character displacement as a result of the competitive exclusion between these two species, maintaining their parapatric distributions. The Amazonian population belongs to a single species, Trogon rufus Gmelin 1788, but with two highly distinct forms that we designate as Trogon rufus rufus in the Guiana Shield and Trogon rufus sulphureus in S & W Amazonia, for which Todd\'s amazonicus is synonymised. They are morphologically and, to a lesser extent, vocally distinct across the lower Rio Negro and matrix of highland and open habitats of the Rio Branco basin but show limited character exchange between the 52-58th parallels west on the southern bank of the Amazon, centred around the Rio Arapiuns on the left bank of mouth of the Tapajos. We postulate that this is the result of secondary contact as a consequence of shifts in the course of the main channel of the Amazon River at times of lower sea levels during the Plio-Pleistocene. T .r. sulphureus is identified by a typically coppery uppertail with subterminal tailband of greener hue, yellow eye-ring, low barring density and broad black bars of the undertail and wing-coverts barring with and lack of a pectoral band. They are also sometimes distinguishable in song by a higher frequency introduction note and/or more pronounced descending modulation across the loudsong. This varies clinally on a west-east gradient, from strong-coppery to shiny olive-green uppertails with more to less distinct subterminal tailbands, diminishing black bar widths with corresponding increasing density and decreasing intro note low frequency. T. r. rufus have green uppertails, blue eye-rings, presence or absence of a white pectoral band and denser undertail and wing panel barring with thinner black bars. These characters were shown to change as a function of geographic distance between specimens of sulphureus and rufus, connected via the \'Arapiuns contact zone\', suggesting isolation by distance. This is reminiscent of a ring species pattern and two specimens with a possible mixture of characters were indeed found from the upper Rio Negro and in Pantepui, where T. r. rufus and T. r. sulphureus would be expected to come into contact, effectively \'closing the ring\'. Whether Trogon rufus constitutes a valid ring species requires further testing, preferably including molecular characters, but this clearly illustrates that the distinction between clinal variation and ring-species is a matter of degree, not kind, with the formation of the ring-species necessarily passing through a clinal stage with no overlap between terminal taxa. We therefore propose the concept of a loop species, where the terminal forms do not overlap but are connected via a series of intergrading populations. It seems likely that such patterns are more widespread in Amazonia than presently known due to the propensity for clinal variation and parapatric speciation lended by its massive geographical extent and abundance of biogeographical semi-permeable barriers. With regards to the population from the Pernambuco Center of Endemism, the few records suggest that it is a valid taxonomic unit. It has the unique combination of a song very similar to T. r. sulphureus due to the high introduction note frequency and pronounced descent in frequencies across the loudsong, with a corresponding widening range but moderately large size, serrated bill and blue eye-ring but this certainly requires confirmation. This requires urgent attention, as the remnant population is very small and localised, recorded only from the Murici municipality, Alagoas. / Nós revisamos a taxonomia do complexo Trogon rufus sob o conceito Biológico de Espécies. Unidades taxonômicas possíveis, quebras e zonas de transição taxonômicas foram definidas usando mapas de calor e isofenas (linhas de contorno de fenótípo) baseados em caráteres de cor, barramento e morfometria. Esses possíveis táxons foram testados pelas análises de discriminantes. Dados de coloração foram obtidos por meio de espectrometria, e os padrões de barramento por meio de fotos de alta qualidade. Nós encontramos quatro espécies biológicas distintas Trogon chrysochloros Pelzeln 1856, da Mata Atlântica, diagnosticável pelo barramento mais escuro e denso na face inferior da cauda e coberteiras da asa, maior tamanho corpóreo, canto mais rápido, com mais notas e de frequência mais alta. Suas partes superiores (cabeça, dorso e cauda) variam de azul a verde acobreado com o aumento da altitude. O bico também é relativamente menor e mais serrilhado, o que está ligado a uma dieta que consiste quase exclusivamente de grandes artrópodes, fazendo desta espécie o Trogon mais insetívoro do mundo, o que deve ser a razão de sua relativa raridade quando comparado a outros Trogonidae com os quais vive em simpatia. Trogon tenellus Cabanis 1862, da América Central, e Trogon cupreicauda Chapman 1914, do Chocó-Magdalena, formam um caso clássico de espécies biológicas, entrando em contato no extremo noroeste da província de Chocó, na Colômbia, sem a presença de formas intermediárias. T. tenellus é identificável pela face superior da cauda azul ou azul esverdeado, anel perioftálmico azul ou cinza, tarso cinza, e voz com de 2 a 4 notas, maior duração das notas e maior mudança entre frequência de pico e frequência alta entre a nota introdutória e nota principal. Essas características contrastam com a cor verde-oliva brilhante da face superior da cauda, anel perioftámico amarelo, tarso geralmente oliva, presença de marrom claro na face inferior da cauda das fêmeas e canto com entre 6 e 8 notas, de menor duração, pouca mudança na frequência entre a primeira nota e o canto principal de T. cupreicauda. Este varia clinalmente de azul para uma plumagem mais verde acobreada e de barramento preto mais espesso para mais fino em uma gradiente da costa do Pacífico, do noroeste do Equador até o Vale do Magdalena. A maior distinção de estados de caráter relativa a T. tenellus na região onde os dois grupos se encontram provê uma possível evidência de deslocamento de caracteres como resultado de exclusão competitiva entre estas duas espécies, mantendo suas distribuições parapátricas. A população amazônica pertence a única espécie biológica Trogon rufus Gmelin 1788, mas com duas formas altamente distintas que designamos como Trogon rufus rufus do Escudo Guianense, e Trogon rufus sulphureus no sul e oeste da Amazônia, com a qual amazonicus de Todd é sinonimizada. Estas são morfologicamente, e em menor escala, vocalmente distintas nas duas margens do baixo Rio Negro e áreas abertas e/ou montanhosas da bacia do Rio Branco, mas apresentam troca de caracteres limitada nas longitudes entre 52 e 58 Oeste na margem sul do Rio Amazonas, centrado nos arredores do Rio Arapiuns, na margem esquerda da foz do Tapajós. Nós postulamos que isto é um resultado de contato secundário, como consequência de mudanças no curso principal do Rio Amazonas em tempos de níveis mais baixos do mar durante o Plio-Pleistoceno. T. r. sulphureus é identificado pela coloração tipicamente acobreada da face superior da cauda com uma banda sub-terminal de tonalidade esverdeada, anel perioftálmico amarelo, barras negras espessas e de baixa densidade na face inferior da cauda e nas coberteiras das asas e pela ausência de uma faixa peitoral. Em certos casos eles também podem ser distinguíveis pela voz com uma nota introdutória de maior frequência e/ou uma modulação descendente mais pronunciada no canto principal. Este grupo varia clinalmente em gradiente de oeste para leste, de uma coloração cobre forte até verde oliva na face superior da cauda com faixa sub-terminal mais ou menos distinta, anel perioftálmico azul, presença ou ausência de uma faixa peitoral branca e barramento na face inferior da cauda e coberteiras de menor espessura e, consequentemente, maior densidade. Nossos dados apontam que estes caracteres mudam linearmente entre sulphureus e rufus de acordo com a distância ao longo de uma gradiente clinal em forma de laço do Oeste Amazônico até o Escudo das Guianas, conectado pela zona de contato de Arapiuns, sugerindo isolamento por distância. Isto sugere um remanescente de um padrão de espécie em anel. Além disso, dois espécimes com possível mistura de caracteres foram de fato encontrados no alto Rio Negro e Pantepui, onde se espera que T. r. rufus e T. r. sulphureus entrem em contato, fechando o anel efetivamente. Ainda é necessário testar se Trogon rufus constitui uma espécie em anel válida, preferencialmente usando dados moleculares, mas este caso ilustra claramente que a distinção entre variação clinal e espécie em anel é uma questão de grau e não de tipo, com a formação de espécie em anel necessariamente passando por um estágio clinal sem sobreposição entre os grupos terminais. Nós assim sugerimos o conceito de espécie em laço, onde as formas terminais não se sobrepõem, mas são ligadas através de uma série de populações onde há fluxo gênico. Parece provável que estes padrões são mais amplamente distribuídos na Amazônia do que é sabido atualmente devido a uma propensão à variação clinal e especiação parapátrica causada por sua grande extensão geográfica e abundância de barreiras geográficas semipermeáveis. Em relação a população do Centro de Endemismo Pernambuco, os poucos registros sugerem que esta é uma unidade taxonômica válida. Este grupo apresenta uma combinação única de canto muito similar ao de T. r. sulphureus, devido à alta frequência da nota introdutória e pronunciada modulação descendente ao longo do canto principal, com uma maior amplitude da frequência, combinada a maior tamanho, bico serrilhado, e anel perioftálmico azul, mas isso requer confirmação. Este caso demanda atenção urgente, já que a população remanescente é muito pequena e de distribuição restrita ao município de Murici, em Alagoas.