Effects of Specimen Age on Plumage Color

The Auk 125(4):803–808, 2008  The American Ornithologists’ Union, 2008��. Printed in USA.

Jessica K. Armenta,1 Peter O. Dunn, and Linda A. Whittingham

Department of Biological Sciences, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin 53201, USA

Abstract.—��Museum specimens �� are�� valuable�� for�� studies�� of�� plumage�� color�� in�� birds,�� but �� feather�� color�� may� fade �� over�� time�� and�� not�� accurately reflect the colors of live birds. In particular, it has been suggested that ultraviolet (UV) color may be more susceptible to degradation than human-visible colors. We used a reflectance spectrophotometer to measure feather color in five species of passerines for which museum specimens were collected consistently over the past 100 years. We found that the feather colors of museum specimens collected within the past 50 years were related closely to the feather colors of live birds. In fact, over a wide range of different colors, we found little change in color measurements for recent (<50 years old) specimens. Furthermore, UV color was not affected more severely by fading than human-visible colors when we confined our analyses to recent specimens. These results provide strong support for the continued use of museum specimens to examine coloration in birds, provided that the specimens were collected relatively recently. Received 5 January 2007, accepted 25 February 2008.

Key words: ��color, fading, �� �museum�� ��specimens,�� ��re��fl��ectance� ��spectrometry,�� ��ultraviolet�.

Efectos de la Edad de los Especímenes sobre el Color del Plumaje

Resumen.— ��Los� especímenes�� de�� museo�� son�� valiosos�� para�� estudiar�� el�� color�� del�� plumaje�� en�� las�� aves,�� pero �� el�� color�� de�� las�� plumas�� podría�� perderse a lo largo del tiempo y no reflejar los colores de las aves vivas. Específicamente, se ha sugerido que el color ultravioleta (UV) podría ser más susceptible a degradarse que los colores visibles por los humanos. En este estudio, empleamos un espectrofotómetro de reflectancia para medir el color de las plumas en cuatro especies de aves paserinas para las cuales se habían coleccionado especímenes constantemente durante los últimos 100 años. Encontramos que los colores de las plumas de los especímenes de museo coleccionados en los últimos 50 años se relacionaron cercanamente con los colores de las plumas de aves vivas. De hecho, a través de un amplio espectro de colores, encontramos pocos cambios en las medidas de color para especímenes recientes (coleccionados hace menos de 50 años). Además, el color UV no fue afectado más severamente que los colores visibles a los humanos al limitar nuestros análisis a especímenes recientes. Estos resultados apoyan fuertemente el uso continuado de especímenes de museo para examinar la coloración de las aves si los especímenes han sido coleccionados en tiempos relativamente recientes.

Museum study skins are widely used to assess plumage color Marchetti 2005) found that UV coloration may be even more sus- (e.g., Schmitz-Ornés 2006) and to study the evolution of color ceptible to fading in specimens than the colors humans can see. traits and sexual dichromatism in birds (e.g., Owens and Hart- Thus, it is not clear whether museum specimens accurately repre- ley 1998, Dunn et al. 2001). However, feather color can be suscep- sent the color patterns and variation seen in live birds. tible to fading over time, so recent studies have expressed concern It is also possible that certain types of feather colors differ in over the use of museum specimens (Winker 1997, McNett and their susceptibility to fading. Feather color is generally produced Marchetti 2005, Maley and Winker 2007). The measurement of either by a pigment or the microstructure of the feather (McGraw color has recently been improved by the use of reflectance spec- 2006a, b; Prum 2006). The two most common pigments are ca- trophotometers, because these instruments provide an objective rotenoids, which are responsible for most bright yellow, orange, measurement of color and are able to measure ultraviolet (UV) and red colors (McGraw 2006a), and melanins, which are respon- wavelengths invisible to humans (Bennett and Cuthill 1994). Al- sible for most brown and black colors (McGraw 2006b). UV, white, most all birds can see in the UV wavelengths (Burkhardt 1989), and blue are common structural colors (Prum 2006). McNett and and UV-reflecting plumage appears to be quite common among Marchetti (2005) suggested that carotenoid-based and UV colors birds (Eaton and Lanyon 2003). A recent study (McNett and were more susceptible to fading than others.

1Present address: �D��epartment�� of� ��Biology,� ��Lone�� S��tar� ��College�-�Cy��F��air, �Cypress,�� ��Te�x�as� ��77��433, ��USA. E-mail��: [email protected]

The Auk, Vol. 125, Number 4, pages 803–808. ISSN 0004-8038, electronic ��ISSN�� 1�9��38-4254.  2008 by The American Ornithologists’ Union. All rights reserved. Please direct all requests for permission to photocopy or reproduce article content through the University of California Press’s Rights and Permissions website, http://www.ucpressjournals. com/reprintInfo.asp.�� DOI: 10.1525/��au��k.2008.0�7��00�6

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McNett and Marchetti (2005) measured the plumage colors or caught in nest boxes (Tree Swallows) and released after mea- of 10 species of wood warblers (family Parulidae); however, they surement. These species were chosen for live measurements be- were able to compare recently collected specimens with older cause they were readily available at the UWM Field Station, specimens (collected before 1935) for only 2 of these 10 species. whereas the other three species were unavailable. In the present study, we measured feather color of five species of All reflectance measurements of plumage color were made passerines for which we had series of specimens that were col- with an Ocean Optics USB2000 spectrophotometer and a PX-2 Xe- lected consistently over the past century. We examined the effect non light source (Ocean Optics, Dunedin, Florida) and calibrated of specimen age on feather colors over the 100-year period to de- against a WS-1 white standard, which reflects >98% of light from termine whether some or all museum skins, regardless of age, are 250- to 1,500-nm wavelengths. A black rubber test-tube stopper suitable for studies of plumage color variation. Researchers can mounted on the end of the probe held the probe at a 90° angle to choose to avoid using specimens that appear to the human eye to the feathers and kept it at a fixed distance from the feathers. Reflec- be faded, but they may not be able to avoid unseen fading in the UV tance measurements were made from 320 to 700 nm, because this range. Therefore, we also examined whether the effect of specimen spectrum encompasses the bird-visible spectrum (Burkhardt 1989). age on feather color was more severe in UV wavelengths than in Representative color patches were selected for each species (Table 1), human-visible wavelengths. and each color patch was measured five times per specimen. Color calculations.—Each reflectance measurement was Methods transformed into variables of hue, saturation, and brightness using the program SPECTRE (see Acknowledgments). All cal- Data collection.—In November 2005 and August 2006, at the Field culations were performed twice, once for the UV spectrum (320– Museum of Natural History in Chicago, Illinois, we measured spec- 400 nm) and once for the human-visible spectrum (400–700 nm). tral reflectance of plumage colors from 147 specimens of five species SPECTRE calculates brightness as the amount of light reflected of passerines (Table 1). The five species sampled were well repre- by the sample in relation to the amount of light reflected by the sented in the collection and had been collected consistently over the white standard. The program calculates saturation and hue using past 100 years. We selected these five species to represent commonly the segment classification method of Endler (1990). McNett and found colors for inclusion in our study (Table 1). We limited our sam- Marchetti (2005) used similar methods for estimating color. Seg- pling to adult male specimens that were not visibly molting. We in- ment classification is advantageous in this type of study, because cluded only specimens whose feathers were not worn or dirty, but we it describes the shape of the reflectance curve and can be applied did not avoid specimens that appeared to be faded. Most specimens without specific information about the visual system of the animal were collected from midwestern states, and within each species most (Endler 1990). This method divides the human-visible spectrum specimens came from the same state or a neighboring state. Most of (400–700 nm) into four equal regions that are approximately the the specimens were collected during the breeding season (late spring violet–blue, green, yellow–orange, and red wavelengths. For anal- to summer). Specimen collection dates ranged from 1892 to 2003. yses of the UV spectrum, we restricted the segments to 320–400 In addition, we measured plumage reflectance of three live nm; thus, each of the four equal segments covered 20 nm. Sat- Tree Swallows (Tachycineta bicolor) and 13 Common Yellow- uration is calculated as a point in two-dimensional space based on throats (Geothlypis trichas) caught at the University of Wisconsin- the relative reflectance of each segment (Endler 1990). For example, Milwaukee (UWM) Field Station in Saukville, Wisconsin (30 May in the human-visible range, one axis is defined by the relative differ- to 5 June 2006). Birds were mist netted (Common Yellowthroats) ence in reflectance between the red and green segments. The other

Table 1. Mixed-model ANOVA testing the effect of specimen age, spectrum (UV or human-visible), and their interaction on brightness, saturation, and hue of avian plumage in five species. Separate analyses were conducted for brightness, saturation, and hue. For brevity, the effect of spectrum (UV or human-visible) is not shown (see text). P values are shown, with significant values in bold (P < 0.017 after Bonferroni adjustment). Results of the independent variable spectrum are omitted for brevity. P values with an asterisk remained significant when analyses were restricted to recent (<50 years) specimens, and a double asterisk indicates P values that became significant when analyses were restricted to recent specimens.

Age Spectrum*age interaction Body Species n Color region Brightness Saturation Hue Brightness Saturation Hue

Eastern Bluebird 24 Rust Breast 0.99 0.051 0.55 0.32 0.23 0.66** Blue Back 0.96 0.22 0.18 0.02 <0.01 0.06 Black-throated 26 Blue-gray Back 0.04 <0.01 0.26 <0.01 <0.001 0.74 Blue Warbler White Belly <0.01 <0.001* 0.99 <0.01 0.06** <0.001 Northern Cardinal 41 Red Breast <0.001 0.76 <0.01 0.90 0.08 <0.01 Common Yellowthroat 50 Yellow Throat 0.23 0.02 <0.001* 0.40 0.02 <0.001* Black Cheek 0.81 0.20 0.93 0.77 0.15 0.19** Brown Back 0.99 0.30 0.04 0.04 0.85 <0.01 Tree Swallow 22 Green Back 0.57 0.001 0.99 0.21 0.47 0.30 White Belly <0.001* 0.06 0.30 0.25 0.45 <0.01

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Fig. 1. Brightness of four colors of museum specimens over time. Closed circles and thick lines represent human-visible brightness (400–700 nm), whereas open circles and thin lines represent brightness in the UV range (320–400 nm). Brightness does not change with age in green (A), brown (B), or yellow (D), but decreases with age in red (C) (see Table 1 for P values).

axis is defined by the relative difference in reflectance between the sampling) and the spectrum (UV or human-visible) were included yellow–orange and violet–blue segments. Saturation is calculated as independent variables. Specimen age was treated as a continuous as the Euclidean distance between one point on the red–green variable and spectrum as a categorical variable. Because each speci- axis and the other point on the yellow–orange to violet–blue axis men was effectively sampled twice in this analysis, once as a UV (equation 16 in Endler 1990). As the relative difference between re- measurement and once as a human-visible measurement, the speci- flectance of the segments increases, so does saturation, such that men identification number was included as a random effect. red would have a higher saturation than pink. Hue, the portion We were also interested in determining whether more recent of the electromagnetic spectrum where the sample shows maxi- specimens would be more suitable for use in plumage color stud- mum light reflectance, is the attribute that is commonly thought ies and, thus, we categorized all specimens as either “recent” (<50 of as “color,” such as red or blue (Bennett et al. 1994). Hue is an years since collection or live) or “old” (>50 years since collection). angular variable, such that values of hue rotate 360° around the Fifty years was chosen as the cutoffage after we examined changes axes defined by the four segments. It is calculated as the arcsine in color variables over time, and also because a gap in the collec- of the product of the difference between the reflectance of the tion record for most species occurred ~50 years ago (Fig. 1). Re- yellow–orange and violet–blue segments divided by the saturation cent specimens included 6 of 24 Eastern Bluebirds (Sialia sialis), (equation 17 in Endler 1990). Within each spectrum, the values for 14 of 26 Black-throated Blue Warblers (Dendroica caerulescens), brightness, saturation, and hue for the five repeated samples were 23 of 41 Northern Cardinals (Cardinalis cardinalis), 38 of 50 Com- averaged for each body region of each bird. mon Yellowthroats, and 10 of 22 Tree Swallows. Separate mixed- Statistics.—We performed a mixed-model analysis of variance model ANOVAs were performed for recent specimens to determine (ANOVA) on each color patch of each species for brightness, satu- whether significant age and interaction effects (spectrum*age) were ration, and hue. Brightness, saturation, or hue was included as the attributable to the inclusion of older specimens. dependent variable in each analysis, and specimen age (the num- Finally, not all body regions of a specimen are affected equally ber of years between the specimen collection date and the date of by normal handling and storage conditions (e.g., specimens are

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usually stored on their backs with their bellies up), and so we performed mixed-model ANOVAs to examine the relationship between body region and specimen age. All museum specimens and live birds were included in these analyses, with brightness, saturation, or hue as the dependent variable. Specimen age and body region were included as independent variables, with specimen number and species included as random effects. In all mixed- model ANOVAs, we used a Bonferroni adjustment of our level of significance (to 0.017), because the same data were used three times to produce estimates of hue, saturation, and brightness.

Results

There was no effect of specimen age on rust, blue, or black plumage colors, but other colors showed variable effects of age (Table 1). Blue-gray, white, and red showed a significant decrease in brightness with age (Table 1 and Fig. 1). Both recent and older specimens were variable in brightness (Fig. 1), so age was not a reliable pre- Fig. 2. Reflectance from the white belly of Black-throated Blue Warblers. dictor of brightness. Saturation and hue also decreased over time Lines are averages from recent (<50 years old, thin, n = 14) and old (>50 years in some colors but not in others. For example, the saturation of old, thick, n = 12) specimens. Differences between recent and older speci- yellow and green decreased with specimen age, but the satura- mens were not tested statistically but are shown here for illustrative purposes. tion of white increased with age in the Black-throated Blue War- The UV range is 320–400 nm, and the human-visible range is 400–700 nm. bler, though not as strongly in the Tree Swallow (P = 0.06). In the case of blue-gray, saturation decreased with specimen age in the None of the interaction terms were significant for brightness. human-visible spectrum but increased with specimen age in the Therefore, the brightness of plumage was generally not fading faster UV spectrum. Only yellow showed an increase in hue with speci- at UV than at human-visible wavelengths when the analysis was re- men age. Interestingly, a significant decrease in brightness over stricted to recent (<50 years old) specimens (Table 1). The decrease in time did not necessarily result in a significant change in either sat- plumage reflectance of the yellow throat of Common Yellowthroats uration or hue, or vice versa (Table 1). Differences between the UV was not greater in the UV than in the human-visible wavelengths and human-visible sections of the spectrum were almost always (comparing live and all museum specimens), and the reflectance of significant (spectrum effect: all P < 0.02); the human-visible spec- the yellow was almost identical between live birds and recent spectrum typically had higher values of brightness, saturation, and imens (<2% difference; Fig. 3). This difference between live and hue than the UV spectrum. We found a significant interaction between spectrum (UV and human-visible) and specimen age for the brightness of some colors but not others (Table 1), which indicates that fading occurred at different rates in different parts of the spectrum. In two colors, the blue of the Eastern Bluebird and the brown of the Common Yellowthroat, UV brightness decreased, whereas human-visible brightness increased with specimen age (Fig. 1). For two other colors, the blue-gray and white of the Black-throated Blue War- bler, brightness decreased with age, and the decrease was faster in the UV spectrum than in the human-visible spectrum (Fig. 2). Saturation and hue are not necessarily predicted to change in the same direction for both the UV and human-visible spectra, because they depend on the shape of the reflectance curves within each spectrum (UV and human-visible), and the shape of the reflectance curve is usually different between the two spectra. Therefore, we did not attempt to interpret the interaction terms for saturation and hue. By contrast, when only recent specimens were included in the mixed-model ANOVAs, most colors showed no significant effect of age on brightness, saturation, or hue. Indeed, only the bright- Fig. 3. Reflectance from the yellow breast of Common Yellowthroats. ness of the white belly of Tree Swallows (F = 10.1, df = 1 and 10, P = Lines are averages from live (dashed, n = 13), recent (<50 years old, thin, 0.02), saturation of the white breast of Black-throated Blue War- n = 25) and old (>50 years old, thick, n = 11) specimens. Differences be- blers (F = 12.4, df = 1 and 14, P < 0.01), and the hue of the yellow tween live birds, recent specimens, and older specimens were not tested throat of Common Yellowthroats (F = 7.3, df = 1 and 38, P = 0.01) statistically but are shown here for illustrative purposes. The UV range is were influenced by specimen age in recent birds. 320–400 nm, and the human-visible range is 400–700 nm.

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Table 2. Mixed-model ANOVA testing the effect of specimen age and become dirtier over time, perhaps from handling, are likely to in- body region (back, belly, breast, cheek) on brightness, saturation, and hue crease in saturation. Indeed, museum specimens with large patches of five species. Separate analyses were performed with brightness, satu- of white often looked “dirty” to us in comparison to live birds. ration, or hue as the dependent variable. Specimen identity and species White may be most susceptible to change because it has the highest were included as random factors in each model (n = 163 specimens). brightness and overall reflectance of all colors. We also found that body region influenced whether the color Variable or interaction Brightness Saturation Hue faded over time. The belly was most severely affected by fading. Age <0.001 0.012 0.015 This may be attributable to storage conditions, because specimens Body region <0.001 0.003 <0.001 are usually stored on their backs, with their bellies facing upward. Age*body region <0.001 <0.001 0.057 Alternatively, the fading may be a result of handling of specimens over time, given that the belly is often touched when specimens are handled. Plumage color in some other body regions, such as the wings, may also be affected by handling; however, we did not mea- recent specimens disproportionately affected one portion of the sure wing color, so further study is warranted. spectrum, however, so it was enough to cause a significant differ- Like McNett and Marchetti (2005), we found that most col- ence in hue between the two groups. ors were affected by age in older specimens. However, when we We found evidence that some body regions, regardless of restricted our analyses to recent specimens, we found few effects species, were affected more severely than others by specimen of age on feather color. It is possible that the effects of time in re- age. In mixed models with body region and species as random cent specimens were masked by small sample sizes, a slow rate of factors (Table 2), the interaction term between age and body re- change, and high individual variance in specimen color. Such a gion was significant for brightness (F = 15.8, df = 4 and 163, P < slow rate of change in color, however, suggests that researchers 0.001) and saturation (F = 6.0, df = 4 and 163, P < 0.001), but not could use recent specimens with some confidence. In particular, for hue (F = 2.3, df = 4 and 163, P = 0.057). The particular body re- for researchers interested in UV coloration, we did not find that gion affected by age was not the same for brightness and satura- colors fade faster in the UV than in human-visible wavelengths, as tion. For brightness, only measurements of the belly, which was was reported by McNett and Marchetti (2005). the brightest region, declined with specimen age, whereas the McNett and Marchetti (2005) suggested that the greater de- brightness of the other body regions was relatively unaffected by crease in brightness in the UV than in the human-visible wave- specimen age. For saturation, only measurements of the cheek lengths would result in changes in hue and saturation, because hue increased with age. and saturation are calculated on the basis of the relative brightness of the four color segments (Endler 1990). In all the colors that we Discussion measured, however, we found that a change in brightness was not necessarily related to a change in hue or saturation. The difference We were able to obtain measurements of both museum specimens between our results and those of the previous study are probably at- and live birds for two species, the Common Yellowthroat and tributable to our use of a series of more recent museum specimens. the Tree Swallow. For these two species, we found that museum McNett and Marchetti (2005) compared live birds with specimens specimens collected within the past 50 years accurately reflected that were mostly collected before 1935. Our use of more recent feather colors of live birds. Time did not play a strong role in the specimens seems to eliminate most of the change in color associ- color variation found among recent (<50 years old) specimens ated with age that they observed. The reflectance of yellow from re- over a wide range of different colors; this effect may be attribut- cent museum specimens almost exactly matched the reflectance of able, in part, to small sample sizes. Furthermore, UV wavelengths live Common Yellowthroats (Fig. 3), in contrast to figure 3A in Mc- were not affected more severely by fading than human-visible Nett and Marchetti (2005). Another possible explanation for the wavelengths, when we confined our analyses to recent specimens. difference in results between studies is that the specimens exam- By contrast, several colors differed with specimen age in old (>50 ined by McNett and Marchetti (2005) may have been prepared us- years old) specimens. If we categorize colors by the mechanism ing a preservative that decreased UV brightness but did not affect used to produce them, we found that structural (green, blue-gray), human-visible brightness. This type of accidental staining, which melanin-based (brown), and carotenoid-based (yellow, red) colors would be invisible to the human eye, has been found in some mu- all differed with specimen age in old specimens. In recent speci- seum specimens (Pohland and Mullen 2006). Unfortunately, in- mens, some structural (white) and carotenoid-based (yellow) col- formation about whether a preservative was used on a specimen, ors changed with age, though the changes were less than those or about what type of preservative was used, is rarely available for observed in old specimens. Therefore, change in feather colors older specimens. Although preservatives were once commonly over time was not related to the color, including UV, or to the used, most recent specimens are prepared without added preserva- mechanism that produced the color. tives (Winker 2000). It is also possible that specimen color could be White appears to be the color most susceptible to changes over affected by washing during preparation, either through removal of time. The white of Tree Swallows decreased in brightness over time, stains and dirt on the plumage or through an effect of detergent on even in more recent specimens. Also, the white of Black-throated the reflectance of feathers. Unfortunately, preparators usually do Blue Warblers showed an increase in saturation over time. Satura- not record whether a specimen has been washed. tion is very low in a pure white color, so changes in reflectance at any The present study strongly supports continued use of mu- wavelength will increase saturation (Fig. 2). Thus, specimens that seum specimens in examining plumage coloration in birds,

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provided that the specimens were collected recently. Results of Maley, J. M., and K. Winker. 2007. Use of juvenal plumage in diag- studies using older specimens may need to be interpreted with nosing species limits: An example using buntings in the genus caution, given that many colors are quite susceptible to changes Plectrophenax. Auk 124:907–915. in hue, saturation, or brightness. Our results emphasize the im- McGraw, K. J. 2006a. Mechanics of carotenoid-based coloration. portance of continued collecting, because many large compara- Pages 177–242 in Bird Coloration, vol. 1: Mechanisms and Mea- tive studies would not be feasible using only live birds. surements (G. E. Hill and K. J. McGraw, Eds.). Harvard University Press, Cambridge, Massachusetts. Acknowledgments McGraw, K. J. 2006b. Mechanics of melanin-based coloration. Pages 243–294 in Bird Coloration, vol. 1: Mechanisms and Mea- We thank J. Bates, S. Hackett, and D. Willard at the Field Museum surements (G. E. Hill and K. J. McGraw, Eds.). Harvard University of Natural History in Chicago, Illinois, for access to specimens. Press, Cambridge, Massachusetts. J. Berges, K. Winker, K. Yasukawa, and two reviewers provided McNett, G. D., and K. Marchetti. 2005. Ultraviolet degradation helpful comments on the manuscript. This work was supported by in carotenoid patches: Live versus museum specimens of wood National Science Foundation (NSF) DEB-0215560 to P.O.D. and warblers (Parulidae). Auk 122:793–802. L.A.W. and by an NSF graduate research fellowship to J.K.A. The Owens, I. P. F., and I. R. Hartley. 1998. Sexual dimorphism in birds: program SPECTRE is available at www.uwm.edu/~pdunn/Spectre/ Why are there so many different forms of dimorphism? Proceed- Spectre.html. ings of the Royal Society of London, Series B 265:397–407. Pohland, G., and P. Mullen. 2006. Preservation agents influence Literature Cited UV-coloration of plumage in museum bird skins. Journal of Orni- thology 147:464–467. Bennett, A. T. D., and I. C. Cuthill. 1994. Ultraviolet vision in Prum, R. O. 2006. Anatomy, physics, and evolution of structural col- birds: What is its function? Vision Research 34:1471–1478. ors. Pages 295–353 in Bird Coloration, vol. 1: Mechanisms and Bennett, A. T. D., I. C. Cuthill, and K. J. Norris. 1994. Sexual Measurements (G. E. Hill and K. J. McGraw, Eds.). Harvard Uni- selection and the mismeasure of color. American Naturalist versity Press, Cambridge, Massachusetts. 144:848–860. Schmitz-Ornés, A. 2006. Using colour spectral data in studies of Burkhardt, D. 1989. UV vision: A bird’s eye view of feathers. Jour- geographic variation and taxonomy of birds: Examples with two nal of Comparative Physiology A 164:787–796. hummingbird genera, Anthracothorax and Eulampis. Journal of Dunn, P. O., L. A. Whittingham, and T. E. Pitcher. 2001. Mating Ornithology 147:495–503. systems, sperm competition, and the evolution of sexual dimor- Winker, K. 1997. A new form of Anabacerthia variegaticeps (Fur- phism in birds. Evolution 55:161–175. nariidae) from western México. Pages 203–208 in The Era of Eaton, M. D., and S. M. Lanyon. 2003. The ubiquity of avian ultra- Allan R. Phillips: A Festschrift (R. W. Dickerman, Ed.). Horizon violet plumage reflectance. Proceedings of the Royal Society of Communications, Albuquerque, New Mexico. London, Series B 270:1721–1726. Winker, K. 2000. Obtaining, preserving, and preparing bird speci- Endler, J. A. 1990. On the measure and classification of colour in mens. Journal of Field Ornithology 71:250–297. studies of animal colour patterns. Biological Journal of the Lin- nean Society 41:315–352. Associate Editor: K. Winker

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