Hummingbirds are some of the smallest birds in the world, with most species being 3-5 inches long as adults. However, they start out even tinier as hatchlings and nestlings before reaching full adult size. So just how small are baby hummingbirds when they first leave the safety of the nest?
Size at Hatching
Hummingbird eggs are very tiny, often not much bigger than a jellybean. However, once the chick hatches out of the egg, it will already have doubled or even tripled in size from its days as a developing embryo in the egg. Here are some details on the size of hummingbird chicks when they first hatch:
- Ruby-throated Hummingbird chicks hatch at 0.6 grams and around 1 inch long.
- Black-chinned Hummingbird hatchlings weigh 0.5 grams and are 0.98 inches long.
- Anna’s Hummingbird chicks hatch out at around 0.65 grams and 1.1 inches long.
- Rufous Hummingbird hatchlings are approximately 0.55 grams and 0.8 inches long.
- Calliope Hummingbird new hatchlings are the smallest at just 0.45 grams and 0.59 inches long.
As you can see, the smallest species of hummingbirds like Calliopes hatch out at not much more than half an inch long and weighing less than a penny. But they grow incredibly fast…
Size After 2-3 Weeks in the Nest
Baby hummingbirds develop at a very rapid pace, needing to be ready to leave the nest in just 2-3 weeks in most species. Here is how quickly they grow in that time:
- Ruby-throated Hummingbirds reach 1.8 grams and 1.7 inches after 2 weeks.
- Black-chinned Hummingbirds hit 2 grams and 1.8 inches by 3 weeks old.
- Anna’s Hummingbirds get to 2.1 grams and 1.9 inches by week 3.
- Rufous Hummingbirds reach 1.8 grams and 1.5 inches after 2 weeks.
- Calliope Hummingbirds may weigh 1.3 grams and be 1.2 inches long at 2 weeks old.
In just a couple weeks, the chicks have often grown to over triple their original hatchling size. Their wings and tails start to develop feathers, although their bodies will still be mostly covered in fuzzy down.
Size Right Before Fledging
In the 24-48 hours before a baby hummingbird fledges (leaves) the nest, it will be very close to adult size but still weighing a bit less. Here are the sizes they reach right before taking their first flights:
- Ruby-throated Hummingbirds average 3.4 grams and 2.4 inches before fledging.
- Black-chinned Hummingbirds reach around 3.2 grams and 2.6 inches before leaving the nest.
- Anna’s Hummingbirds weigh 3 grams and are 2.5 inches long pre-fledging.
- Rufous Hummingbirds get to 3 grams and 2.3 inches before fledging.
- Calliope Hummingbird nestlings may be 2.3 grams and 2 inches right before fledging.
In all species, the wings and tail will be fully feathered at this point, allowing the young birds to take flight. They are still small and delicate though, weighing just a fraction of their adult size.
Size Comparison to Adults
To understand just how tiny hummingbirds are when leaving the nest, it helps to see how they compare to full grown adults of the same species:
| Species | Fledgling Size | Adult Size |
|---|---|---|
| Ruby-throated | 2.4 inches, 3.4 grams | 3-4 inches, 3-4 grams |
| Black-chinned | 2.6 inches, 3.2 grams | 3.5-4 inches, 3-4.5 grams |
| Anna’s | 2.5 inches, 3 grams | 3.5-4 inches, 4-6 grams |
| Rufous | 2.3 inches, 3 grams | 3-3.5 inches, 3-3.5 grams |
| Calliope | 2 inches, 2.3 grams | 2.75-3.25 inches, 2.6-3.5 grams |
As you can see, hummingbirds fledge at anywhere from 67% to 90% of adult size. They have nearly all their feathers and look remarkably like miniature versions of their parents. But they have a lot more growing and filling out to do over the coming weeks and months.
How Big Do Hummingbird Chicks Get Each Day?
The incredible speed at which hummingbirds develop as chicks is seen when you look at their daily growth rate:
- Ruby-throated Hummingbirds gain about 0.2 grams per day.
- Black-chinned Hummingbirds add around 0.18 grams daily.
- Anna’s Hummingbirds put on 0.22 grams each day.
- Rufous Hummingbirds grow by 0.17 grams a day.
- Calliope Hummingbirds increase just 0.14 grams daily.
This rapid weight gain requires the parents to constantly bring small spiders and insects to the nest for the chicks to eat. The high-protein diet allows them to nearly double their hatchling weight in just a week or two.
Changes After Leaving the Nest
Once a baby hummingbird fledges, its size will continue changing as it matures:
- Their wings will get longer and broader.
- Their tail feathers will grow fuller.
- Their body will fill out and put on more weight.
- Females are larger than males when mature.
- The bill will darken from an orange-yellow to black.
- Juvenile plumage transitions to adult colors.
- Growth normally levels off in 6-8 weeks.
Young hummingbirds face high risks and mortality rates in their first year of life. But if they can make it to adulthood, they may live 5 years or more in the wild.
Key Takeaways on Fledgling Size
Here are some key points to remember on the tiny size of baby hummingbirds when they first leave the nest:
- They fledge at 2-3 weeks old in most species.
- Their body is around 2-2.6 inches from bill to tail.
- Weight ranges from 2-3.5 grams depending on species.
- Wings and tail fully feathered for flight.
- Still finishing growing over next few weeks.
- Weigh around 2/3 to 90% of adult hummingbird size.
- Very vulnerable and high mortality rate at this stage.
Conclusion
While hummingbird chicks start out absolutely tiny when they hatch at less than an inch, they grow remarkably fast. In just over two weeks, they reach nearly full adult proportions, just on a smaller scale. Fledgling hummingbirds weigh only a few grams but have perfectly formed wings, tail, and feathers to allow immediate flight. Their rapid development is essential for these delicate birds to survive once leaving the nest. But they still have much maturing and filling out to do in the coming weeks to reach full adult size and colouration. Watching a mother hummingbird care for her tiny chicks in the nest and then seeing the fledglings take their first flights is an incredible experience.
