We have certainly had no shortage of storms this winter. Perhaps you have wondered how birds can deal with the cold, the wind, and the snow to survive such challenging spells of bad weather. The research done on birds’ ability to anticipate storms has provided some insights but much remains to be done. In today’s column, I’ll discuss the results of two recent papers that shed light on the effect of impending storms on bird behavior.
The first paper by Henry Streby of the University of California and colleagues was published earlier this year in the journal Current Biology. The researchers had 20 Golden-winged Warblers fitted with geo-locators in April of 2013. These small dataloggers continuously record light-levels and time. From the data, a researcher can track the longitude and latitude of a migrating bird. Birds must be captured so that the data from the geolocator can be read.
In April of 2014, Streby and colleagues tracked the arrival of nine of these marked birds back to their mountainous breeding territory in northeastern Tennessee from wintering areas in South America. The birds arrived in Tennessee between April 13 and April 27, 2014.
Between April 27 and April 30, a massive storm that spawned over 80 tornadoes developed over the middle of the United States. The eastern Tennessee Golden-winged Warblers were able to detect the impending storm well before it arrived. What did the birds do? All nine of the warblers vacated their breeding grounds. Five of them did return after their storm and their geolocators were resampled. All five of these birds took evasive action to avoid the storm.
On April 27, tornadoes were being generated from Kansas to Texas. By the following day, the storm was less than 100 miles from the Golden-winged Warblers’ breeding area. The storm was quite powerful when it arrived in northwestern Tennessee, generating winds of over 100 mph.
But the wind posed no problem for the five warblers. They had moved to Florida’s Gulf Coast, beyond the range of the storm. One of the birds even flew to Cuba.
How did the birds know the tornadoes were coming? The authors believe that the birds were detecting infrasound, sound whose frequency is far too low for humans to hear. Tornadoes generate infrasounds that are propagated through the ground.
Storms are usually associated with low-pressure systems so falling barometric pressure could be a cue that a storm is approaching. A recent paper by Creagh Breuner and colleagues examined this phenomenon. The paper was published in 2013 in the Journal of Experimental Biology.
When humans hear that a blizzard is approaching, we see a run on groceries, batteries and candles. Shouldn’t birds prepare for inclement weather as well? The Breuner team addressed this question by studying White-crowned Sparrows on the breeding grounds at high altitude in Montana. Spring snowstorms are frequent.
In particular, the researchers searched for a relationship between falling barometric pressure and behaviors that might help the birds weather the storm. The researchers predicted that falling barometric pressure should cause an increase in mass (due increased feeding rate_, an increase in the rate at which fat is deposited and hormonal changes associated with stress. They also did experiments on captive birds by artificially lowering the air pressure and looking for changes in behavior.
The results were mixed. The authors clearly showed that the sparrows could detect changes in barometric pressure in their lab experiments. In the field, falling barometric pressure did not result in an increase in mass or in stress hormone production. The researchers did find a significant relationship between fat deposition and barometric pressure but the effect was very slight. In the lab, birds sometimes increased their feeding rate as pressure dropped but again stress hormone levels did not change. We have much more to learn about these intriguing responses.
[Originally published on March 1, 2015]