Comparing Flight Abilities and other Behaviors of Crows with

Wind Speed in a High-wind Winter Environment

Mathew SharplesWinter 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 Nocturnal Migration Spring Nocturnal Migration

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)

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’sWundermap.

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 Sources of Error• 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.

• 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.