- Black Chinned Hummingbird Nesting
- Dan & Diane True
Twenty-six Black-chinned hummingbird nests
were observed over a three year period by my wife, Diane, and
I in Texas and New Mexico. Some nests were in trees. Nesting
platforms known as Hummingbird Houses served as sites for other
nests. Hummingbird Houses were installed under eaves, porch ceilings,
and covered patios.
Migrating female hummingbirds
follow males in spring into the United States and Canada from
wintering grounds in Mexico by three to ten days. The birds come
north for one purpose: to raise young, and they waste no time
in getting down to business. Nest construction generally begins
the day they arrive. Distended abdomens on some of the hens indicated
those little birds arrived impregnated.
This little hen is so heavy
with eggs we can't see her feet because they have been absorbed
by her feathers.
Top priority in a female hummingbird's
mind for nest site selection is: nest in a geographical area
where temperatures are likely to remain 96 degrees F or less
throughout her nesting cycle. Her reason is, she aims for an
egg incubation temperature of 96 degrees. If the temperature
rises above 96 and remains above that level for several hours,
(or days) her eggs will "cook", killing the embryo.
This probably explains why areas where summer temperatures soar
into the 100s see their arriving hummers "disappear"
in May. The little birds "disappeared" because they
were really only passing through on their way to cooler climate
locations in our northern states and Canada. Invariably the little
rascals "reappear" in late July and early August, and
pause to show us their youngsters before humming on south to
wintering grounds in Mexico and Central America. A few Ruby-throats
don't follow the crowd and remain behind in hotter states. These
birds are often found in states with mountains high enough in
altitude to experience a summer with less harsh temperatures...the
Ozark's and Appalachians, for example. (The air cools at a rate
of 5.5 degrees F per 1,000 feet rise in altitude.) However, a
few Ruby-throats remain at low altitudes in states that can sizzle
in the summer. These hardy souls have learned a unique way to
escape egg cooking temperatures.
The temperature within a stand
of broadleaf trees will average 5 to 7 degrees cooler than open
or urban areas. This is due to the tree's transpiration, which
provides natural, evaporative air conditioning within the tree's
umbrella. (An average oak transpires 50 gallons of water per
day.) A very small population of Ruby-throats have discovered
this natural phenomena and attempt to nest at altitudes where
summer temperatures almost always exceed 100. In those cases
nests are often found on the low branch of a broadleaf tree overhanging
a body of water. Female Ruby-throats have apparently found the
thin layer of cool air created by evaporation from the water's
surface. That thin layer of cool air, combined with the tree's
5 to 7 degrees worth of cooling, creates a micro environment
matching northern climates. Note that hummingbirds migrate to
nesting areas where humans go to escape summer's heat...'way
north, the mountains, or a lake.
The rule for eastern states is,
if you have females in June, it is likely the birds are nesting
with you. No females in June says they are nesting elsewhere,
and elsewhere is probably somewhere up north. (In Arizona and
southern California, Anna's hummingbirds avoid egg cooking temperatures
by choosing to nest in January and February. Costa's hummingbirds
avoid the desert heat by humming up to nest in those state's
mountains.) The female's second priority for nest location is:
Find a place out of the wind.
The importance of selecting a
nest site that is protected from the wind was emphasized from
the experience of Jay and Carrie Hollifield of Roswell, New Mexico.
Winds catapulted ten hummingbird eggs out of five nests from
elm branches in their ranch yard in 1999. In Amistad, New Mexico,
broken hummingbird eggs were often found on the ground by Dave
Dunnigan after strong winds raked his ranch yard. 8 to 10 Black-chinned
hummingbirds nest around Dunnigan's place each year. One of his
little hens was so determined to nest out of the wind she built
down low, 18 inches above the ground, on a bush snuggled in the
shelter of a hen house. It is probable this bird was not a first
year mom, but rather an experienced mom who had suffered the
consequences of high winds in a previous nesting season. This
suggests hummingbirds ae capable of learning. In May of 2000,
five of Dunnigan's hummers chose to nest on Hummingbird Houses
placed under his porch eaves, out of the wind. In Roswell, Hummingbird
Houses are installed at the Hollifield place, however a dozen
pairs of cliff swallows dominate choice nesting sites under their
eaves. One of those Hummingbird Houses was even taken over by
Nests we observed were established
in places providing as much wind protection as was available.
They were sheltered either by an outer perimeter of trees, or
by buildings. Six to twelve feet above the ground in the first
row of inner branches where protection is increased from weather
elements were prevalent tree locations. Trees of choice, in order
of preference, were sycamore, fruitless mulberry, maple, elm,
and Russian olive. Note the larger the leaf, the higher the preference.
A fork in a branch about 18 inches
from its end was a repeating tree nest location. The chosen branch
averaged 1/4" in diameter...too small to support a cat,
but dangerously whippy in high winds. A hen's search image includes
the coincidence of either a large leaf or a cluster of leaves
three inches or less directly above the fork. She utilizes this
leafy "umbrella" to protect her nest against sun and
rain, and to shield her eggs and chicks from prying predator
Nest construction averaged five days. She brings materials to
her site at a rate of 34 trips per hour. The little hen's first
load of material is spider webbing. She applies that material
as a sticky foundation on the forked area of her nest site. Thereafter,
her sequence is orderly. She airlifts plant down or other soft
material in her beak and tucks it into the fork. After shaping
and molding that material, she flies in another load of spider
webbing. Most often she carries a glob of webbing clinging to
the underside of her beak, under her throat, and down across
her breast. Transfer of the webbing onto her nest is achieved
by pressing her chin and breast against the nest and wiping the
webbing onto her work. Stickiness of spider webbing appeared
to be the only element binding the nest. Frame by frame scrutiny
of video tapes revealed no sign that she used her spittle as
glue. In that regard, for her little system to produce enough
spittle to construct her nest seems beyond a hummingbird's physical
Bits of camouflage followed the
spider webbing and were applied to her work-in-progress. Another
load of plant down was followed by spider webbing followed by
a bit of camouflage, and so on. Four hours straight was usually
her work schedule before she quit for the day. Some of the little
hens worked mornings, others were afternoon types. Since developing
eggs burdens her with extra weight throughout nest building,
it made sense that she work on the nest no more than four hours
Concealing her work from its beginning
is probably a reason the female hummingbird camouflages her nest
as she builds. One hen was so picky about hiding her work that
on the sun bleached side of a branch she chose light colored
camouflage material to match. On the shaded, and therefore darker
side of that same branch, she camouflaged that side of the nest
darker to match that side's coloration. Such attention to detail
created a nest that was camouflaged slightly differently on each
side. Hummingbird House nests were camouflaged against the color
of the eave, ceiling, or patio cover where the House was installed.
Sometimes the hens gathered flakes of paint chips from the building
and applied the chips to their nest. A male bird was never seen
near a hummingbird nest. So, where is Daddy Bird during the female's
flurry of nest building activity?
Flashy gorgets transform Daddy
Birds into Mr. Neon. To protect her children from predators,
the female would be foolish to tolerate a male spotlighting her
work during nest building, or during chick raising. In whatever
ways hummingbirds communicate, after she has been impregnated,
a probable reason we don't see hummingbird males near hummingbird
nests is that she has told Daddy Bird to take his brightly colored
flashy suit and hum off.
Molding the nest's wall as the nest progresses upward was done
by pressing the top edge between her wing and body, as a potter
shapes soft clay on a spinning vase.
Hummingbird hen shaping
her nest's edge between her wing and body.
Rounding the nest's inside was
done by ramming her little bottom, with tail feathers straight
up, against inner walls. She tamps the nest's floor by hanging
on with one foot and stomping rapidly with her free foot. Since
her weight is about that of a penny, hanging on with one foot
and stomping with the other to pack the nest's floor allows her
leg muscle power to compensate for her light weight. She stops
work occasionally and simply sits in her nest, as if resting.
The little hens are so focused they ignore photo equipment moved
in increments to as near to them as five feet. One photo revealed
a unique pattern in the structure of hummingbird nests, a pattern
that was previously unknown.
Backlighting a nest revealed that
the lower half was thick and dense while the upper half was thin
enough to let some light pass. She probably incorporates this
feature so that she can adjust air circulation to maintain an
egg incubation temperature of 96 degrees F, which is 5 degrees
less than her normal body temperature. On cold days, she maintains
egg temperature by positioning her body below the thinner, upper
half of the nests walls hold warmth inside her nest. On hot days,
raising her body above the thinner portion of the nest's wall
would increase air circulation and allow excess egg incubation
heat to escape. These smart little birds refine this construction
feature even more.
For additional precision of egg
temperature control, the windward side of the upper wall is thicker
than its lee side.
Nest with thinner, almost
"see through" upper wall on downwind side. Note side
facing camera, the side facing the prevailing wind, is thicker.
The "thickest" side
of the upper wall invariably faces into prevailing wind patterns.
That suggests she fashions the windward side of her nest to give
her eggs protection against the probing fingers of a cool wind.
Further, their first nests, those constructed in the relative
cool of early spring, have thicker and therefore warmer upper
walls than second nests built in summer. Another refinement in
hummingbird nest building is that their spring nests are deeper
than their summer nests. On cool days the hens snuggled down
so deep inside their nests their beaks and tail aimed straight
up. On warmer days they sat so high in the nest and were fully
visible. The eggs in one nest were "cooked" during
a record heat wave that spawned eight straight days of high temperatures
ranging between 100 and 103 degrees F. Those eggs failed to hatch.
Sometimes a nest was only half finished before the hen laid her
First egg in a half finished
Without exception, the hens skipped
one day before laying their second egg. In proportion to body
weight, hummingbird eggs are the largest in the bird world. If
human babies were proportional to hummer eggs, we would give
birth to 25 pound babies. A long handled mechanics mirror was
used to check a nest when a hen flew off to feed. Activity
was watched from a distance through binoculars and a telescope.
Clues that a hen was "in labor" came when she settled
on her nest and alternated between wiggling and shaking a few
moments. In one case we knew within ten minutes when a hen's
first egg arrived.
New chick with hatching
Incubation time on each nest was
16 days with one exception...a 12 day period in Texas. (That
hen was smaller, and her behavior different from other Black-chinns
we observed. The hen may have been a member of the smaller sub-species
of Black-chinned Dr. Bill Baltosser believes exists.)
- When the nest held eggs, it appeared
the hen flew into and out of the nest in a way that reduced the
chance of downwash from her wings blasting an egg out of her
nest. In the split second during either launch or landing, she
seems to tilt her wings in a way that would direct her wing downwash
away from the nest's opening. In one nest it apeared that downwash
from her hovering flight ejected one egg, which crashed on the
ground. The hen abandoned that nest and its remaining egg.
Chick feeding intervals averaged
twenty minutes. Without exception the moms brooded their chicks
through eight nights. The ninth they spent somewhere other than
on the nest. Chicks at that age were feathered enough to regulate
their own temperatures. The two chicks were large enough by then
that their little bodies stretched the nest and filled it side
to side, with their backs almost flush with the nest's rim. This
age, nine days, is the earliest observation of youngsters humming
When the chicks were 21 to 22
days old, the mother hummers began construction on a second nest
while still feeding her first two nestlings. Fledge time for
the chicks was commonly 23 days, however some where 24 or 25
days old before they left the nest. Individual chick fledge time
is probably tied to its level of nourishment. First flights were
usually no farther than the nearest branch.
Chick making first flight.
While continuing to work on their
second nests, the busy mom hummers located and fed the newly
flying chicks through two to three days before they were on their
own. While building her second nest the first egg often appeared
during the time she was feeding her two fledged chicks. The common
view held by most ornithologists about hummingbirds reusing an
old nest is that they don't. We found a different answer.
One tree nest was reused by a
different mom hummer almost before it had time to cool from previous
use. Two Hummingbird House nesting sites were reused by different
moms within a day or two after the first chicks fledged. Those
three nests were home to a total of 12 hummingbird chicks during
one nesting season. We think these nests were reused because
they were still intact and in good condition. Few hummingbird
nests survive the winter months, and those that do are so dilapidated
they are not reusable. However, we found several cases where
a new nest was built on top of an old nest. One site had a stack
of four nests, probably covering four years. One of the little
hens nested a third time. Her third set of chicks were only a
month old before they pointed their little beaks south and hummed
with her and their siblings toward wintering grounds in Mexico.
Some nests were exquisite, woven
by hens that worked with great skill. Others were less than perfect.
Differences in building skills likely resulted from first time
nesters being less adept at nest building than experienced moms.
Many times one female would hover a short distance from another
female that was busy with nest building. The busy female invariably
ran the intruder away. However, when the busy female left to
gather more building material, the intruder would zip in and
either steal nesting material, or hover all around the nest as
if inspecting the work, possibly to gain building skills of her
own. It also seemed as though an intruding female was considering
a take over. In one instance, during her first day of nest building
one female was building six nests simultaneously. Each was about
20 feet apart and all were on Hummingbird House platforms. During
the second day she narrowed her building activity to three of
the six. On the third day she cut her work down to two. On the
fourth day she abandoned work on one and finished the other during
her fifth day. In two other instances one female worked on two
nests simultaneously before abandoning one and finishing the
A roadrunner raided one New Mexico
tree nest, ants killed two day old chicks in another, and a Texas
hailstorm destroyed another. The Hummingbird House nesting sites
had no weather or predator problems.
Two nests became unattended when the mothers apparently met with
unknown fates. One mom had collected fiberglass from somewhere
and used the glass for lining her nest. We suspect she may have
died from an overdose of fiberglass. In our determination to
not disturb the nesting process, we waited two days after her
disappearance to intervene. Her chicks were dead. After one full
day of the other mom's absence, we placed one of her starving
orphans in an active Black-chinned nest built on a Hummingbird
House, and the other orphan in an active Magnificent nest in
a tree. What must have been two surprised hummingbird mothers,
both accepted and fed the third chicks. The second day after
these transfers, the Magnificent nest was empty and that mother
not seen again. It is probable the nest was raided by a predator.
Meanwhile, back at the Hummingbird House Black-chinned nest,
three growing chicks soon created a space problem. The two largest
chicks crowded the smaller chick outside the nest, where it hung
by a tiny toenail hooked to spider webbing fourteen feet above
the ground. The problem was solved by installing the orphaned
chick's "old" birth nest side by side with its new
nest and putting the toe-nail-hanging chick alone back in its
original nest. The mother continued to feed all three chicks
and they all fledged.
Although we learned lessons from
tree nests, we learned more from the Hummingbird House nests
because they provided an ambiance that allowed intimate observations
from the nest's beginning to its end .
To see a hummingbird nest in action,
check under the porch ceiling of County Line Barbeque in Albuquerque,
New Mexico, between May 1 and August 30. Two moms nested there
on Hummingbird Houses in the summer of 2000. Since hummers tend
to return and breed in the area where they were raised, if both
little hens survive the winter, they should return to the restaurant,
along with surviving daughters in 2001. It is probable that between
3 and 6 nests will be built and occupied there in the summer
of 2001. (Three hens returned and were nesting under County Line's
porch ceiling as of May 24, 2001.) The total number of nesting
hummers from year to year in the restaurant's developing hummingbird
colony will depend on how many moms and their daughters survive
the winters. Extra Houses are in place for additional moms. In
2002, there could be 6 to 10 hummingbirds raising chicks in nests
under County Line's porch.
Hummingbird banders have established
the average life-span of female hummers to be 3 1/2 years. Average
male life-span is 2 1/2. Black-chinned record longevity is 7
The longest Black-chinned migration on record
is that of a male banded at Sonita, Arizona, in July of 1988.
In April of 1991, this little guy was recovered a few miles NNW
of Manzanillo, Mexico, 930 miles south of Sonita. This was the
first documented hummingbird flight linking the US and Mexico.
Here's to many more.
Dan & Diane True
Authors of "Hummingbirds of North America".
- May 24, 2001 update: Observations
gained so far during this 2001 nesting season have caused us
Picture this: A hen heavy with eggs is looking for a place to
build a nest. At the same time, winds are blowing hard, gyrating
tree branch nest sites so violently as to make nest building
difficult to impossible. Desperation, plus the urgency of eggs
about to arrive forces her to build on a porch light fixture,
or other device such as our Hummingbird House, neither of which
is gyrating because they are protected from the wind. Picture
the same situation on a day with steady rain. The urgency of
eggs about to arrive forces her to search for a nest site while
it is raining. Trees are wet and dripping. Again, she finds a
porch light fixture, or our Hummingbird House, both of which
are dry during the rain. Being smart, she builds a nest there
and successfully raises her family.
We think the above may explain
those occurrences when hummingbirds build their nests in "strange
places", such as under porch ceilings, under the eaves of
a home, or in an open building such as a garage.
Want to know how many hummingbirds you are
feeding? The Hummer Counter by Best-1
is a 32 ounce glass feeder calibrater and marked to answer that
often asked question. At around $14.00 from your local bird supply
store, or from the manufacture Best-1, Box 998, Poteet, TX 78065;1.800.772.3604.
- Owning this feeder gives you a valuable tool
in providing an accurate count of your year to yearhummingbird
population...an important addition to our hummingbird information.
- Please stay tuned, for further updates.
Dan & Diane True