Ruby-throated hummingbirds (Archilochus colubris) are a species of hummingbird found throughout eastern North America. They are known for their metallic green upperparts and grey-white underparts, as well as the bright ruby-red throat patch found on adult males. Ruby-throated hummingbirds are migratory, spending winters in Central America and returning to North America in the spring to breed. This brings up the question – do ruby-throated hummingbirds mate in September, as they prepare to migrate south for the winter?
Quick Answer
Yes, ruby-throated hummingbirds do mate in September. Though they have a relatively short breeding season from spring through summer, ruby-throats are known to have a second nesting period in late summer to early fall before they migrate for the winter. During this time, the males and females will mate again to produce another clutch of eggs.
Ruby-throat Migration and Breeding Season
Ruby-throated hummingbirds generally arrive back in the United States and southern Canada in April and May to establish breeding territories. The males arrive first to scout out locations, followed by the females approximately one week later. Once the females arrive, breeding occurs – the male performs aerial courtship displays, culminating in mating with the female.
The female then builds a tiny, cup-shaped nest out of plant down, spider silk, and lichen, laying 1-3 pea-sized eggs. She incubates the eggs alone for 10-14 days. Once hatched, the chicks are fed by the female every 1-2 hours, fledging after 18-28 days. By late summer, this first brood has reached independence.
Sometime in August through September, as the days shorten indicating winter’s approach, the hummingbirds instinctively know they will soon migrate south. Before leaving, they participate in a second, shorter breeding season to produce another clutch of offspring. The males establish new territories, court females, and mate again before embarking on their long migration in late September.
Behaviors and Displays During Fall Mating
During this fall mating period, male ruby-throats will perform their elaborate courtship displays to entice females again. These displays involve flying in repeated horizontal loops, diving and ascending in vertical U-shaped patterns, and buzzing back and forth in rapid flight. If a female shows interest, the male may fly in rapid nose-dives or in a pendulum motion to impress her further.
Receptive females allow the males to approach closely. Mating occurs while perched or on the wing, and lasts only a few seconds. Though the males do not take part in nesting duties, they may continue guarding and displaying to females to mate again before migration.
Throughout September, females once again build nests, lay eggs, incubate, and care for hatchlings – though this breeding period is abbreviated compared to spring-summer. The goal is to produce a viable clutch that can survive after the parents leave on migration. By late September, most ruby-throats have departed until the following spring.
Environmental Cues for Breeding and Migration
What prompts ruby-throated hummingbirds to begin this pre-migratory breeding period? Several environmental cues are involved:
- Decreasing daylight hours – less daylight simulates winter approaching and triggers migration instinct
- Changes in food availability – fewer flowers in bloom at summer’s end
- Cooler temperatures
- Internal circannual rhythms – an endogenous clock helps birds “know” when to breed and migrate
These seasonal cues all send signals that migration time is near. This initiates a hard-wired behavior to mate again to produce offspring, continue the species, and take advantage of conditions before the long migration south.
Differences Between Spring and Fall Breeding
While the behaviors and process are similar, there are some key differences between the primary spring breeding season and fall mating period:
Spring/Summer Breeding | Fall Breeding |
---|---|
– Begins when birds arrive in March-April | – Begins in August-September before migration |
– Nesting territories strongly defended | – Shortage of food reduces territory defense |
– Males display frequently to attract mates | – Less energetic displaying by males |
– 1-3 clutches laid through summer | – Typically only 1 fall clutch |
The key difference is that the main breeding period lasts much of the spring and summer, resulting in multiple nests and clutches. The fall mating period is shorter, more opportunistic, and focused on reproducing just once more before the migration south.
Benefits of Fall Mating
What are the advantages of ruby-throats having this secondary mating period in the fall? Some potential benefits include:
- Taking advantage of late summer food sources to support breeding
- Producing offspring that can continue the population while parents are gone
- Maximizing reproductive success before eight months away in migration
- Increasing genetic diversity by mating again with new partners
Overall, late summer mating allows ruby-throated hummingbirds to capitalize on favorable conditions and reproduce one more time before their long journey south. This late breeding bolsters the species’ chances of survival.
Challenges of Late Breeding
However, there are some challenges that come with this fall mating strategy as well:
- Declining food sources make feeding more difficult
- Cooler weather increases thermoregulation needs
- Shortened season limits time to successfully fledge chicks
- Parental investment is lost when parents migrate away
- Predation risks to eggs, chicks, and females while nesting
These obstacles can make successful breeding harder to achieve. But for ruby-throats, the effort is worth taking the gamble on another clutch before migration.
Conclusion
In conclusion, ruby-throated hummingbirds definitively do mate in September before their annual migration back to Central America and Mexico. The shortening daylight hours and other environmental cues trigger an innate behavioral program to produce one more clutch. This pre-migratory breeding happens swiftly in August through September.
While challenging, this second mating period allows ruby-throated hummingbirds to reproduce again when conditions allow. This late breeding enables more offspring to bolster the species’ numbers, improves chances some will survive the parents’ long absence, and expands genetic diversity. Therefore, though brief, the fall mating period is an important part of ruby-throats’ breeding strategy and life cycle.
This shows that though small, hummingbirds have evolved complex migratory and breeding adaptations to thrive. Their ability to capitalize on favorable conditions in September before migrating exemplifies their remarkable behavioral and reproductive strategies.