Comparing Flight Abilities and
other Behaviors of Crows with
Wind Speed in a High-wind
Winter Environment
Mathew Sharples
Winter Ecology, “Spring” 2012
Mountain Research Station
University of Colorado at Boulder
Potential Consequences of High Winter Winds on
Corvid Behavior – American Crow (Corvus
brachyrhyncos) and Common Raven
(Corvus Corax)
• Birds must feed daily: how crows/ravens keep warm all winter.
• Persistent high wind storms, common in the Nederland area in
winter, may keep birds grounded/unable to fly high and search
for food or unable to reach caches.
• If the birds are grounded for extended periods or restricted to
localized flight, this could tax their energy reserves/force them
to rely on caches that may or may not be abundant.
• Crows/ravens prefer open areas, more exposed to wind than
forest-dwellers. (Goodwin 1986, Heinrich 1989)
• Decreased communication ability, especially in flight?
Introduction: Wind Affects Birds
(of course!)
• May seem intuitive that “wind affects birds”, but there’s been
research done on how wind speed effects migrants. However,
no research was found on how consistently high local winter
winds may effect bird ecology, behavior, and survival.
• The Nederland crows tended to fly lower/between close objects
during higher winds. The literature has also found a correlation
with wind speed and elevation above ground: “By comparison,
altitude of migrants tended to increase during lower wind
speeds in both diurnal and nocturnal migrants.” (Thomas et al.
2011)
• Thomas et al. (2011) point out that, “Zehnder et al.(2001)
reported a decrease in migration intensity with an increase in
wind speeds, arguing that stronger winds are inconsistent,” (this
matches my observations of increased variance in wind speed
at any given moment with increased wind speeds) ”and
therefore not favored by migrating birds.”
Fall Diurnal Migration
-For some reason, the
authors did not create a
graph for spring diurnal
migration and only
examined wind direction in
regard to that time of year.
(Thomas et al., 2011)
Fall Nocturnal Migration
Spring Nocturnal Migration
Hypothesis
• As wind speed increases, there should be a
correlative tendency for birds (crows and ravens
most abundant and consistently available to
observe) to more often fly along with the wind,
reducing energy expenditure that would result
from flapping against the wind. (Study ended up
exploring flight effort and not frequency.)
• Also, there should be a terminal point above
which the wind is so hostile as to severely limit
and ultimately prevent flight altogether.
Methods
• Used hand-held anemometer for wind speeds, referred to local weather
station timelogs after observation.
• Compared wind speeds (base and gusts) with observed flight patterns and
behaviors of crows and ravens, mostly the former (being more common),
and compiled patterns based on the “average” of activities displayed during
a certain range of speeds.
• Observed during morning (high activity) and afternoon timeslots, but
afternoon was commonly a low-presence time of day –Goodwin (1986) says,
“flight to the roost begins well before sunset”.
• Observations made on most days between February 6th and 24th.
• Visited multiple sites around Nederland: Chipeta Park, fields at the western
end Barker Reservoir and near the P.O., streets of downtown. Downtown
was a consistent activity hotspot.
• Chipeta and fields seemed to only have activity during mild winds (up to 6.7
m/s / 15 mph) – “leisure” area.
Typical daily
weather graph
from
KCONEDER
stations.
Timelog data
displayed
beneath these
graphs on
wunderground’s
Wundermap.
http://naturemappingfoundation.org/natmap/facts/common_raven_712.html
-Crow call a high-pitched
“caw”, raven call a lower,
guttural croak.
Ravens more hawk-like
(soaring, big), crows
more pigeon-like (don’t
soar, smaller). (Heinrich
1989, Goodman 1986)
Results
• For wind speeds presented, I’m using readings from the
KCONEDER3 station (except a few instances when
KCONEDER16 was higher) –consistently higher winds than
both forested site station and on-ground anemometer readings.
Also using averages of base winds and gusts.
• Higher KCONEDER3 readings probably more accurately reflect
above-ground conditions, the domain of flight. More wind
resistance encountered on ground.
• Little to no harmful effect of high wind speed expected based
on observations. Crows were still able to travel efficiently
(except against the wind) and therefore get to caches/find prey.
(“Food hiding reported” –Madge 1994)
• No flocks were seen heading west during breezy-windy
westerly conditions, and no individuals were going very far
west/higher in windy conditions.
Results
• Since little harmful effect of high wind speed is
predicted based on observations, significance of
study lies in behavioral changes.
• Were never permanently grounded, as winds were
never sustained at extreme levels –extremity only
during some gusts.
• Less “leisure” activity as winds become higher –in
high winds/gusts, no open perching or open ground
foraging (crows mostly feed on the ground – Goodwin
1986) and congregating were observed.
• Winter precipitation seems to have little effect on
behavior. Snowstorm presence does not correlate
with decreased congregating, perching, and foraging.
T is also non-applicable to this study, which was
mostly between -10 and 0 degrees C: fairly static.
s.
Drifting Along Sideways
Discussion: Implications for Crows
• Decrease in open perching with increased
wind speed means they cannot see
predators or foraging opportunities as well.
• Decrease in calling with increased wind
speed means vital communication is more
difficult to share.
• Decrease in foraging/congregating with
increased wind speed. Wind gusts (as low
as 5.63 M/S) will break up a foraging
crowd; do they get scared because they
can’t hear predators above the wind?
Discussion: Effect on Ravens?
• Raven behavior was relatively unaffected
compared to crow behavior (seen performing
same activities in high and light/calm winds,
including acrobatics and open perching anf
foraging in high gusts).
• Only some difficulty in flying west in high wind,
but could still “zig-zag” in highest observed
gusts where ravens were present (+16 m/s).
• Actually used high wind as an easy way to
hover or gain altitude –high wind may actually
confer benefit.
Further Research
• Long-term research needed to
discover more concrete
patterns/to observe behavior
during more high-wind events.
• Interesting observations noted in
terms of flock behavior and wind
speed, which could be greatly
expanded upon.
• Find the terminal speed beyond
which flight is severely hindered –
presumably higher with the
ravens, less bothered by high
winds than crows.
• Relate wind speed to actual
quantifiable frequencies of
behavior.
Sources of Error
• On-ground wind measurements less
accurate than in the sky, where there
are no objects to resist wind.
• Few periods of sustained high winds
that would allow for sharper pattern
definition.
• Incidences of behavior hard to
quantify with limited time/resources –
only generalizations presented, no
allowance for individual stochasticity
that is likely.
• The higher the mean wind speed
becomes, the more variability there is
in wind speed at any given point in
time.
Conclusion
• Significant effect on perching, foraging, open-area
congregations: higher winds lead to less expression of
these behaviors, but short-term suppression of these
behaviors likely has no influence on survival (can visit
caches instead of forage).
• Effects on flight of strong headwinds can be mitigated
to a certain point by plumage maneuvering. Ability to
travel in other directions is usually enhanced by higher
winds.
• High winds may keep crows confined to certain
places/area and effect their ability to hear and see
predators.
• Therefore, crows lead a more confined lifestyle during
high wind events– “confined” from engaging in leisure
activity, hunting properly, etc.
Works Cited
• Heinrich, B. 1989. Ravens in Winter. Summit
Books. New York, NY.
• Goodwin, D. 1986. Crows of the World. British
Museum (Natural History). Suffolk, England.
• Thomas, P., et al. 2011. Effects of Weather on
Avian Migration at Proposed Ridgeline Wind
Energy Sites. Journal of Wildlife Management.
75(4). 805-815.
• Madge, S. 1994. Crows and Jays. Houghton
Mifflin. New York, NY.