Flower Color, Hummingbird Pollination, and Habitat Irradiance in Four Neotropical Forests1

Abstract

Pollinator visual systems differ considerably among broad groupings such as bees, bats, and birds, and it has been proposed that factors shaping the diversity of flower color in tropical plants include differences in pollinator perceptual abilities. Within the pollinators of the Neotropics, one major difference between taxa is that hummingbirds perceive color well across abroad range of wavelengths from 300-660 nm whereas most bees perceive color well over a narrower range spanning 300-550 nm. Thus, hummingbirds can see red and other long-wavelength reflection much better than bees. Another factor that could potentially influence flower color in tropical forests is the difference in light availability among habitats such as gaps, canopy, and forest understory. I conducted a survey of floral color in four Neotropical forests using a portable spectroradiometer to provide an unbiased measure of color reflectance. The primary pollinator agents and light habitats of each plant species were classified using primary literature or accounts of direct observations by experts. Flower color was not influenced by differences in light availability between open and closed habitats but was influenced by pollinator visual systems. Specifically, insect flowers reflected across a broad range of the spectrum but hummingbird flowers reflected mostly long-wavelength light (typically median wavelength >585 nm). Thus, hummingbird-pollinated flowers are not tuned specifically to hummingbird color sensitivity but instead may decrease conspicuousness to bees and other insects that have poor visual sensitivity to long-wavelength color. RESUMENExisten considerables diferencias entre el sistema visual de los diferentes grupos de polinizadores, como las abejas, murcielagos, y aves. La diferencia en la habilidad perceptiva del polinizador ha sido propuesta como uno de los factores determinantes de la diversidad en la coloracion de las flores en plantas tropicales. El rango de longitud de onda percibido por los polinizadores es una de las mayores diferencias entre los taxones: los colibries perciben el color entre un rango de 300 y 660 nm, mientras que las abejas lo hacen en un rango que varia entre 300-550 nm. Por consiguiente los colibries perciben el rojo y otras longitudes de onda mayores mucho mejor que las abejas. Otro factor potencial que podria estar influyendo en el color de las flores en los bosques tropicales es la diferencia en la disponibilidad de luz entre habitats como claros de bosque, dosel, y sotobosque. Lleve a cabo un estudio sobre la coloracion floral en cuatro bosques neotropicales. La reflectancia del color fue medida utilizando un espectro-radiometro portatil, obteniendo asi mediciones de alta precision. Los agentes polinizadores primarios y los ambientes de luz para cada especie de planta fueron clasificados usando referencias literarias y expertos locales. El color de las flores no vario entre los habitats abiertos y los cerrados. Sin embargo se encontraron variaciones relacionadas con el sistema visual de los ...

What hummingbirds can tell us about cognition in the wild

“…Colour might, however, be used to find flowers in unfamiliar places, such as along a migratory route and red may well be more conspicuous against a background of browns and greens that make up a western North American mountain range. It has also been argued elsewhere that the ubiquity of red flowers along the migration route of the rufous has less to do with attracting hummingbirds than making flowers inconspicuous to insects, whose vision is poorer at longer wavelengths (Altshuler, 2003;Briscoe & Chittka, 2001;Raven, 1972).…”

“…Having found that the hummingbirds could learn refill rates, and in experiments on risk sensitivity and contextdependent choice, that they readily learn what (volume and concentration of sucrose) is held in flowers or wells of different colours, it was clear that these birds could learn and remember each of the three (what-where-when) components of episodic-like memory (Hurly & Oseen, 1999;Bateson, Healy, & Hurly, 2002;2003;Morgan, Hurly, Bateson, Asher, & Healy, 2012). They can also remember pairs of these components: they can remember when and where (Henderson et al, 2006a) and they can remember what and where (e.g., Healy & Hurly 1995; 1998) although we have not explicitly looked for whether they can remember what and when together.…”

“…For humans, utility might be measured in terms of energy, finance, or some other useful currency and humans were also always assumed to make rational choices. However, there is now a wealth of data to show that humans do not always make rational decisions and increasing evidence to show that animals, including rufous hummingbirds, also do not make such decisions (Bateson et al, 2002;2003;Hurly & Oseen, 1999;Latty & Beekman, 2011;Morgan et al, 2012;Sasaki & Pratt, 2011;Scarpi, 2011, Waite, 2001. One of the experimental paradigms used to show that rufous hummingbirds are irrational consists of offering birds a choice between two favourable options (a binary choice set; Figure 2) and a choice among three options, the two favourable options from the binary choice set plus a third poorer option.…”

“…One of the experimental paradigms used to show that rufous hummingbirds are irrational consists of offering birds a choice between two favourable options (a binary choice set; Figure 2) and a choice among three options, the two favourable options from the binary choice set plus a third poorer option. If the birds were choosing rationally, the inclusion of the poorer option should not affect the relative preference the birds have for the two favourable options, but it does (Bateson et al, 2002;2003;Morgan et al, 2012). One suggested mechanism for this change in preference is that sampling of the poorer option forces birds to take relatively more of the better of the two favourable options to regain the lost energy.…”

Do Hummingbirds See in Ultraviolet?

“…As a case study, we have used the electroretinogram results of a diurnal bird, the Firecrown hummingbirds. It has been well established that hummingbirds learn to associate the rich nectar contents of flowers with different colors, varying from red to ultraviolet [1][2][3][4][5][6] and it is of particular interest to know the neural bases for such chromatic properties. Avian retinae show a complex array of photoreceptors, including single and double cones with visual pigments of maximal absorption sensitivity ( max ) at long-wavelength-sensitive cone visual pigment (L-cone) with max between 540 nm and 570 nm ; mediumwavelength-sensitive cone visual pigment (M-cone) with max between 500 nm and 507 nm ; short-wavelength-sensitive cone visual pigment (S-cone) with max between 430 nm and 460 nm and violet-wavelength-sensitive cone (V-cone) with max (between 400 nm and 420 nm ) or ultraviolet-sensitivecone (UV-cone) with max (between 360 nm and 370 nm ) [7][8][9].…”