When choosing a mate from a group of potential suitors, a female bird needs to be as picky as possible.  She typically invests a lot more time and energy in the reproductive process and future offspring than a male does, so it’s especially important for her to make the right choice of mate in order to get the most from her male partner, whether he gives her more food while she’s incubating, takes better care of the offspring in the nest, or simply gives her good genes to use in reproduction (Griggio et. al. 2009).


A male budgerigar, Melopsittacus undulatus.


Birds use lots of different factors to determine which mate is better; which is most important varies depending on the species.  No matter what criterion a female uses, however, it must be a characteristic that shows the quality of the male honestly – an accurate representation of the male’s overall health and fitness.  In order for a signal – body size, song, territory size, etc. – to be considered honest, it must first be dependent on the general condition of the animal possessing it, i.e. if a bird is unhealthy or unfit, its signal will be less attractive; conversely, if the bird is totally healthy, its signal will be highly attractive to females (Keyser and Hill 2000).

Feather condition and color is one of the most common factors in female bird mate choice (Zampiga et. al. 2004).  In general, a sick or less fit bird has less time to maintain its plumage, so its appearance reflects its health.  Females are much less likely to mate with a male with unpreened and dirty feathers (Griggio et. al. 2010).

Unlike humans, birds have “tetrachromatic” vision; they have four types cones in their eyes that perceive red, green, blue, and ultraviolet light (Pearn et. al. 2001).  Furthermore, all families of birds contain species which possess feathers that are ultraviolet-colored, meaning they reflect light in the UV range of the electromagnetic spectrum (Eaton and Lanyon 2003).  Only recently have scientists begun to study the effects that UV-reflecting plumage has on female mate choice.


The head of a male budgerigar under UV light.


The purpose of this website is to explain UV-plumage-based female mate choice through the lens of the “four questions” proposed by the animal behaviorist Niko Tinbergen in his 1963 paper “On aims and methods of Ethology.”  The four questions are . . .

            Phylogeny: Also known as evolution, phylogeny describes the history of a given behavior in evolutionary terms, including the ancestral state and selective pressures that may have contributed to the rise of the behavior.
            Ontogeny: Also known as development, ontogeny describes the chronological changes in the behavior during the lifespan of an individual, including the effects of learning.
            Mechanism: Also known as causation, mechanisms can include the physical characteristics used in the behavior, genetic traits, or environmental triggers for the behavior.
            Adaptive Value: Also known as function, adaptive value refers to the increase in survival fitness and reproductive success of the animal due to its performance of the behavior.

Each page of this website will refer to one of Tinbergen’s four questions as it describes the factors that led to the development and propagation of UV-based mate choice in birds.


dragonfly through an eagle's eyes 
These pictures show different views of a distant dragonfly:
the one on the left is with an eagle’s vision,
and the one on the right is what a human would perceive.