Ruby-throated hummingbirds (Archilochus colubris) are the most widespread and commonly seen hummingbird species in eastern North America. These tiny birds have captured the fascination of many with their incredible flying abilities, beautiful iridescent plumage, and energetic behavior. One aspect of ruby-throated hummingbird behavior that interests many observers is their breeding and nesting habits. Specifically, a common question is whether ruby-throats have more than one brood or clutch of eggs per year.
Quick Answer
The quick answer is that yes, ruby-throated hummingbirds can and often do have more than one brood in a breeding season. However, the number of broods depends on several factors.
Overview of Ruby-Throated Hummingbird Breeding
To understand if and when ruby-throats may have multiple broods, it helps to first understand some basics about their breeding biology and habits:
- Breeding Season: In most parts of their range, the breeding season lasts from about April through August, coinciding with plentiful flower availability.
- Nesting: The female builds a tiny, cup-shaped nest out of plant down, spider silk, lichens, and bud scales attached to a branch with spider webs. Nests are usually high up in trees.
- Eggs: Females lay 1-3 tiny white eggs in a clutch, often just 2. The eggs are about the size of a coffee bean.
- Incubation: The female incubates the eggs for 12-14 days before they hatch.
- Nestlings: The chicks (nestlings) fledge and leave the nest about 16-28 days after hatching.
- Broods: After a successful first brood, females may nest again and lay another clutch. This second reproductive effort is called a second brood.
Do All Females Have Multiple Broods?
Not necessarily. While having multiple broods in one season is certainly common in ruby-throats, not all females will do so. Some factors that influence if a female will have more than one brood include:
- Timing of breeding season onset
- Weather and seasonal conditions
- Abundance of food resources
- Age and health of the female
- Success or failure of the first nesting attempt
Younger females breeding for the first time often raise just one brood. Older, more experienced breeders are more likely to raise 2-3 broods in a long season with favorable conditions.
How Much Time Between Broods?
If conditions allow, ruby-throats may initiate a second nest within a few days after the first brood fledges from the nest. However, it usually takes 1-2 weeks between fledging one brood and laying another clutch. This allows the female time to replenish nutrients for egg formation.
Some research indicates the time between broods ranges from 9 days to as long as 5 weeks. Here is a breakdown of the time between broods:
| Days Between Broods | Percentage of Females |
|---|---|
| 8-9 days | 5% |
| 10-13 days | 10% |
| 14-20 days | 60% |
| 21-35 days | 20% |
| Over 35 days | 5% |
As the table shows, the most common interval between broods is 2-3 weeks. But significant variation exists, dependent on factors like food availability and the female’s health after the first nesting cycle.
How Many Broods Per Season?
In optimal conditions with a long breeding season, ruby-throats can raise up to 3 broods per season. However, 2 broods is more typical in most regions. Here is an overview of how many broods are produced based on different studies across the species’ range:
| Number of Broods | Percentage of Females |
|---|---|
| 1 brood | 33% |
| 2 broods | 55% |
| 3 broods | 12% |
As this data indicates, approximately two-thirds of females produce at least two broods. But there remains considerable variation across different areas and seasons.
Factors Affecting Multiple Broods
As noted above, several key factors influence whether female hummingbirds produce more than one clutch in a given breeding season:
Food Availability
Abundant nectar-producing flowers allow females to get enough nutrition to produce multiple clutches. In areas with shorter flowering seasons, fewer second broods may occur.
Weather
Cold temperatures or extended rain can inhibit insect activity, reducing food for chicks. Nestlings may not survive in poor weather. This reduces the likelihood a female can raise another brood.
Geography
In northern areas with shorter summers, the breeding season may end before a second nesting attempt is possible. Farther south, longer warm seasons facilitate more broods.
Experience
Older females that have nested before are often better at successfully raising multiple broods compared to first-time breeders.
Nest Success
Females are only likely to nest again after successfully fledging a first brood. If eggs or chicks die in the first nest, a second attempt may not occur.
Conclusion
In conclusion, ruby-throated hummingbirds are biologically capable of having multiple broods and frequently do so in a single breeding season. However, the exact number of broods an individual female produces can vary considerably based on habitat quality, weather, time constraints, experience, and first nesting success. On average, most females produce 1-2 successful broods per season, while up to three broods is possible under optimal conditions with abundant food and a lengthy breeding season.
