The Ruby-throated Hummingbird (Archilochus colubris) is the sole species of hummingbird that breeds across Eastern North America. This tiny bird, weighing roughly the same as a penny, undertakes a remarkable migratory journey from its wintering grounds in Mexico and Central America. The reproductive cycle is compressed into a short summer window, making the timing of egg laying a precise event upon their return.
Arrival and Start of the Breeding Season
The breeding cycle is directly linked to spring migration, which begins with males arriving along the Gulf Coast as early as mid-March. Males quickly move north, establishing and defending feeding territories in anticipation of the females’ arrival. Females typically follow a week or two later, reaching northern latitudes and Canada by late April or early May.
This northern journey is timed to coincide with the bloom of nectar-producing flowers and the emergence of small insects, which provide the necessary high-energy fuel and protein. Once a female arrives and mates, the breeding process begins immediately, as there is little time before the southward migration in late summer. The male’s involvement ends after mating, placing the entire responsibility of nesting and raising the young on the female.
Nest Construction and Timing of Egg Laying
The female begins nest construction shortly after mating, a process that takes between five and ten days. She selects a concealed location, often on a slender, downward-sloping branch of a deciduous tree, usually 10 to 40 feet above the ground. The finished nest is about the size of a golf ball with an inner cup only an inch in diameter.
The nest is built primarily from soft plant down, such as thistle or dandelion fluff, anchored to the branch using sticky strands of spider silk. This silk provides elasticity, allowing the nest to stretch as the nestlings grow. The exterior is camouflaged with fragments of lichen and moss, which help the cup blend with the tree bark.
Once the nest is complete, egg laying begins in mid-to-late May in the central part of their range, peaking throughout June. The female lays one egg, then waits a day or two before laying the second. The exact timing varies significantly depending on latitude, starting earlier in the southern states and later in the northern regions.
Clutch Size and Incubation Period
The female Ruby-throated Hummingbird almost always lays a clutch of two eggs, though rarely a single egg or three eggs may be found. These are the smallest eggs laid by any bird, resembling tiny, white ovals, weighing less than a gram each. Incubation begins immediately after the second egg is laid to ensure the chicks hatch close to the same time.
The incubation period lasts 12 to 14 days, during which the female sits on the nest for 50 to 55 minutes of every hour. She must briefly leave the nest frequently to forage for the nectar and insects required to sustain her rapid metabolism. Once the altricial young hatch, they remain in the nest for another 18 to 22 days before they are ready to fledge.
Raising Second Broods
In many parts of their breeding range, particularly in the southern United States, females attempt to raise a second brood. This second nesting cycle begins shortly after the first brood has fledged. The female may construct a new nest or refurbish the old one, with new eggs laid in July or early August.
The window for a second brood is shorter, as the birds must build up fat reserves for the autumn migration. Females in the northernmost parts of the range, such as southern Canada, often only have time for one successful nesting attempt. In the deep South, some females may attempt a third brood if conditions remain favorable late into the summer.