Summary: The Evolution Of Hummingbirds

There is a great diversity of bird here on Earth; some are swift fliers, others cannot fly at all, while others are brightly colored or incredibly tiny. The smallest bird known to man is almost insect sized and a species of hummingbird. Hummingbirds are a fascinating variety of bird as they lay the world’s smallest bird eggs and most weigh less than an ounce, however, they are little but powerful, with records of up to 45 mph speed and the ability to cross the Gulf of Mexico, a nonstop 20-hour travel. These miniature birds known as hummingbirds due to the sound that their wings produce in flight is part of the avian family Trochilidae. There are many distinctive shared derived characteristics of hummingbirds, such as their dazzling gorgets, or the light reflecting feathers found on the bird’s throat or chest, their amazing hovering abilities and strong wings, and their long needle-like specialized bill (Smithsonian). Their highly specific bills are used for feeding on certain flowers that must have nectar high in sugar content, be tubular shaped, red or orange in color, may face downwards, and have long stamen for pollen distribution (Smithsonian). According to Johnson, hermit hummingbirds, or genus Phaethornis, live in the tropics or subtropics and their plumage is not drastically different from males and females, as observed with other types of hummingbirds. One of their unique traits is their long curved bills, with red or yellow coloring on the lower bill, that allows hermits to drink nectar from flowers that other hummingbirds cannot reach (Johnson). So although hummingbirds as a family are already specified to feed from certain flowers only, there is further specialization in members of the same genus and even within species. It is important to think about hummingbirds because they play the important role of pollination for many flower species and help to determine the variety and abundance of plant species in the wild. The researchers of the paper, “Evolution of sexual dimorphism in bill size and shape of hermit hummingbirds (Phaethornithinae): a role for ecological causation,” were observing hummingbird bills in hermits and comparing that to other hummingbird species to determine if curvature dimorphism is an ancestral trait, found in the ancestor and all descendants, or a derived trait, only found in hermits. …show more content…
They hypothesized that the difference in bill curvature between the sexes would be greater for the species with the longest bills and questioned if this dimorphism is formed through sexual selection or natural selection (Temeles, Miller, and Rifkin). This research is crucial because it could explain the diversity in hummingbird species and seeks to understand the forces that have and continue to shape the formation of dimorphism. For the study, the researchers examined 856 adult hummingbird specimens from a museum collection to measure bill morphology and wing length. There were approximately 16 males and 13 females observed for each of the 30 species of hummingbirds collected. Each hummingbird was measured for the length in millimeters of the exposed culmen (top part of bill), total bill (bill tip to gape or end of bill), arc length of exposed culmen, and wing cord (wing length when held at 90 degree angle). Equation R=(C/2)/sinA was used to mathematically compare bill curvature, R = radius, C = length of culmen, A = angle of declension measured using a circular protractor. To quantify sexual dimorphism, the researchers used Lovich – Gibbons two-step ratio using species averages, s.d. = (L/S-1) x (+/-1), with L = average size of the larger sex and S = average size of the smaller sex (Temeles, Miller, and Rifkin). Through the numbers calculated, the researchers then constructed three figures to organize and display their collected data. Figure 1 shows that there is many species that display sexual dimorphism in bill curvature with a female bias, bill length with a male bias, wing length with a strong male bias, and a bill arc length with a male bias. Figure 2 displays the numerical value of sexual dimorphism of bill curvature in each species in respect to their evolutionary tree to compare closely related hummingbird species. It shows that most of the hermit species, about 60%, have a large difference between