Pictured here is a mature female Ruby-throated hummingbird (Archilochus colubris), hovering as it feeds from a hummingbird feeder stationed outdoors in Prince Edward County, Ontario. Contrary to the adult males of this species, the females do not share the characteristic ruby red gorget of their namesake, and can be identified instead by their emerald green backs, white throat and breast, and short rounded tail feathers .
Interestingly enough, while the Ruby-throated hummingbird is the only breeding hummingbird in Eastern North America, it maintains the largest breeding range of any known North American Hummingbird, spanning from Central Canada to the Gulf Coasts of the United States and Mexico . Research and observation have indicated that ruby-throated hummingbirds may choose habitats based not on preference, but on a trade-off between feeding requirements satisfied by flowering shrubs and forbs and the shelter from predation offered by the scrub habitat, with some seasonal variation, instead .
While length may vary from 7.5 to 9.0 cm, ruby-throated hummingbirds exhibit reverse sexual size dimorphism; the females of this species typically weighing 3.8 grams, while the males weigh only an average of 3.4 grams . Annual survivorship is 31% for males and 42% for females, with the longest known living males and females having lived 5 and 9 years respectively .
Most hummingbirds, including that of the ruby-throated hummingbird, consume a diet consisting almost exclusively of floral nectar . However, when nectar is scarce, they have been known to feed on small insects and tree sap as well . Intersexual segregation of feeding and foraging is also common amongst this species, in which the dominant and territorial male hummingbirds monopolize the high-quality nectar patches, leaving the females to feed in lower quality foraging areas .
Like many other migratory species of birds, ruby-throated hummingbirds exhibit protandrous migration, in which the males precede the females during migration and arrive at the breeding grounds significantly earlier . Protandrous migration is usually associated with sexual dimorphism, dichromatism, and extra-pair paternity, with the competition for mates driving the males to protandry . Another contributing factor for the males’ propensity for protandry is the polygynous mating system that exists within the species . In order to attract females that enter their established territories, male ruby-throated hummingbirds put on courtship displays including “dive displays” and rapid wing beating, if the female is receptive she may respond with a “mew” call and assume a solicitous posture . Ruby-throated hummingbirds mate from March to July spawning up to three broods annually . The female lays, on average, 1-3 eggs per brood in the nest she builds at the site of her choice, she then proceeds to incubate the eggs and feed the chicks once born; the males do not provide any parental care .
No female ruby-throated hummingbirds sing, the males however, do utter rapid and squeaky calls, mainly those used for agonistic threats, but have no complex songs . Ruby-throated hummingbirds instead, communicate primarily through visual, tactile, and perhaps even olfactory cues .
While predation in not thought to contribute significantly to adult hummingbird mortality, it does exist, with ruby-throated hummingbirds being vulnerable to predation mainly by raptors, blue jays, and domestic cats . While not common, there have been instances of ruby-throated hummingbirds participating in opportunistic anti-predator behaviour observed, such as the mobbing of an American Kestrel and increased vigilance while foraging for food .
The ruby-throated hummingbird is protected under the Migratory Bird Treat between the Canada and United States, as well as being listed under Endangered Species in Appendix II of the Convention of International Trade .
FUN FACT: Did you know that hummingbirds are incredible in ways that most other birds are not? They can fly backwards, upside-down, and hover, they have the fewest number of feathers on any bird, and have wings that beat 53 times per second ! In fact, all this is supported by their astonishingly high metabolic rates, which require 204 calories per gram per hour – in comparison, if a hummingbird was the size of a human, it would consume energy at a rate 10 times that of an Olympic marathon runner .
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Ruby-throated Hummingbird (male) (Archilochus colubris) Northerly Island Chicago Cook County IL September 2015 Week #38 Jeff Skrentny IMG_6193
Macho inmaduro de T. dupontii visitando flores cerca de la entrada del Instituto de Ecología, por la tarde.