Effects of Specimen Age on Plumage Color

The Auk 125(4):803–808 2008 Th� American Ornithologists’ Union, ��2008. Printed in USA. EFFECTS OF SPECIMEN AGE ON PLUMAGE COLOR 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� �� plumage�� color�� in�� birds,�� but �� feather�� color�� may� fade �� over�� time�� and�� not�� accurately reflect the colors �� live birds. I� particular, it has been suggested that ultraviolet (UV) color may be more susceptible to degradation than human-visible colors. W� used � reflectance spectrophotometer to measure feather color in five species �� passerines for which museum specimens were collected consistently over the past 100 years. W� found that the feather colors of museum specimens collected within the past 50 years were related closely to the feather colors �� live birds. I� fact, over � wide range �� different colors, w� found little change in color measurements for recent (<50 years old) specimens. Furthermore, UV color was not �ffected more severely by fading than human-visible colors when w� confined our analyses to recent specimens. These results provide strong support for the continued use �� museum specimens to �xamine 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,�� refl��ectance� ��spectrometry,�� ultraviolet. Efectos de la Edad de los Especímenes sobre el Color del Plumaje Resumen.— ��Los� ��especímenes�� de�� museo�� son�� valiosos�� para�� estudiar�� color�� del�� plumaje�� en�� las�� aves,�� pero �� color�� de�� las�� plumas�� podría�� perderse � �� largo del tiempo no reflejar los colores de las aves vivas. Específicamente, se ha sugerido q�� el color ultravioleta (UV) podría ser á� susceptible � degradarse q�� los colores visibles por los humanos. E� 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 �ños. Encontramos que los colores de las plumas de los especímenes de museo coleccionados en los últimos 50 �ños se relacionaron cercanamente con los colores de las plumas de aves vivas. D� hecho, � travé� de un amplio espectro de colores, encontramos pocos cambios en las medidas de color para especímenes recientes (coleccionados hace menos de 50 �ños). Además, el color UV no fue afectado á� severamente q�� los colores visibles � los humanos al limitar nuestros análisis � especímenes recientes. Estos resultados apoyan fuertemente el uso continuado de especímenes de museo para �xaminar la coloració� de las aves si los especímenes han sido coleccionados en tiempos relativamente recientes. �useum study skins are widely used to assess plumage color Marchetti 2005) found that UV coloration may be even more sus- (�.�. Schmitz-Orné� 200�) and to study the evolution of color ceptible to fading in specimens than the colors humans can see. traits and sexual dichromatism in birds (�.�. Owens and Hart- Thus, it is not clear whether museum specimens accurately repre- ley 1998 Dunn et al. 2001). H�wever, feather color can be suscep- sent the color patterns and variation seen in live birds. tible to fading over time, so recent studies have �xpressed concern I� is also possible that certain types �� 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 200�). Th� measurement of either by � pigment or the microstructure �� the feather (McGraw color has recently been improved by the use �� reflectance spec- 2006a, �; Prum 200�). Th� �w� 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). A�- sible for most brow� and black colors (McGraw 2006b). UV white, most all birds can see in the UV wavelengths (Burkhardt 1�8�) and blue are common structural colors (Prum 200�). 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,�� Tex�as� ��77��433 ��USA. E-mail��: �[email protected] The Auk, V��. 125 Number 4 pages 803–808. ISSN 0004-8038 electronic ��ISSN�� 1��38-4254. 2008 by Th� American Ornithologists’ Union. All rights reserved. Please direct all requests for permission to photocopy or reproduce article content through the University of California Press’� Rights and Permissions website, http://www.ucpressjournals. com/reprintInfo.as�.�� DOI: 10.1525/��au��k.2008.0��00� — 803 — 05_Armenta_07-006.indd 803 10/15/08 5:04:23 PM 804 — ARMENTA, DUNN, AND WHITTINGHAM — AUK, Vol. 125 McNett and Marchetti (2005) measured the plumage colors �� caught in nest boxes (Tree Swallow�) 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 UW� Field Station, specimens (collected before 1�35) for only 2 of these 10 species. whereas the other three species were unavailable. I� the present study, w� measured feather color �� five species �� All reflectance measurements of plumage color were made passerines for which w� had series of specimens that were col- with an Ocean Optics US�2000 spectrophotometer and � PX-2 X�- lected consistently over the past century. W� �xamined the �ffect non light source (Ocean Optics, Dunedin, Florida) and calibrated �� specimen age on feather colors over the 100-year period to de- against � WS-1 white standard, which reflects >�8% of light from termine whether some or all museum �kins, regardless �� age, are 250- to 1500-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 � �0° angle to choose to avoid using specimens that appear to the human eye to the feathers and kept it at � fixed distance from the feathers. R�flec- be faded, but they may not be able to avoid unseen fading in the UV tance measurements were made from 320 to �00 nm, because this range. Therefore, w� also �xamined whether the �ffect of specimen spectrum encompasses the bird-visible spectrum (Burkhardt 1�8�). 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 A�knowledgments). All cal- Data collection.—I� November 2005 and August 2006, at the Field culations were performed �wice, once for the UV spectrum (320– Museum of Natural History in Chicago, Illinois, w� measured spec- 400 nm) and once for the human-visible spectrum (400–�00 nm). tral reflectance of plumage colors from 14� specimens of five species SPECTRE calculates brightness as the amount of light reflected of passerines (Table 1). Th� five species sampled were well repre- by the sample in relation to the amount �� light ��flected by the sented in the collection and had been collected consistently over the white standard. Th� program calculates saturation and hue using past 100 years. W� selected these five species to represent commonly the segment classification method �� Endler (1990). McNett and found colors for inclusion in our study (Table 1). W� limited our sam- Marchetti (2005) used similar methods for estimating color. Seg- pling to adult male specimens that were not visibly molting. W� in- ment classification is advantageous in this type �� study, because cluded only specimens whose feathers were not worn or dirty, but w� it describes the shape �� the reflectance curve and can be applied did not avoid specimens that appeared to be faded. Most specimens without specifi� 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 � neighboring state. Most of (400–�00 nm) into four �qual 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 18�2 to 2003. yses �� the UV spectrum, w� restricted the segments to 320–400 I� addition, w� measured plumage reflectance of three live nm; thus, each of the four �qual segments covered 20 nm. Sat- Tree Swallow� (Tachycineta bicolor) and 13 Common

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