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How Do The Shorter Days Of Fall Affect Animals And Plants?
Posted on Wednesday, September 21, 2011 by eNature
Female Dark-eyed Junco
Female Dark-eyed Junco
© Ken Thomas
Osprey with fish
Osprey with fish
© Terry Ross, CCL

With the fall equinox happening this Friday and fall upon us, we’re now seeing our days rapidly getting shorter. 

Some of us like the change but it seems most folks aren’t too happy to see the days get cooler and nights get longer.

Plants and animals are affected too: it’s these variations in day length that help them set their internal clocks.

Migratory birds are a prime example. A Dark-eyed Junco nesting in northern Canada responds to the first shortening days of summer with a series of physical changes: its reproductive organs become inactive and shrink in size, hormones stimulate the rapid growth of a new set of feathers (its non-breeding plumage), and fat deposits develop to provide fuel for the long migratory flight ahead.

Thus the preparation for migration starts as soon as the days begin to shorten. And the process must operate in reverse when the bird is in its winter habitat in the United States. As soon as days begin to lengthen, the Dark-eyed Junco must gear up physically for the flight north and breeding season. If it fails to do so, it likely won’t survive a long-distance migration.

Plants in temperate zones must also set their calendars accurately in order to flower and, for deciduous species, develop and drop leaves at the optimal time. Plants set their internal calendars using several attributes from the sunlight they receive. In fact, the angle of the sun may be more important to a plant than day length.

That’s because plant cells produce compounds called phytochromes in response to different portions of the light spectrum. Direct sunlight is higher in red light, while indirect sunlight contains more far-red light. During late fall and early winter, when the sun remains low in the southern sky, the indirect light produces an increase in far-red phytochromes.

As spring approaches and the arc of the sun rises in the sky, direct sunlight triggers the production of red phytochromes. The ratio of these two compounds mediates the hormones involved in flowering, leaf drop, and bud development. Even seeds below the soil are affected. It’s true: the amount of red and far-red light that penetrate the soil is sufficient to govern germination.

So the cycle of life and its related migrations and transitions are deeply connected to the heavens.  Really does make you appreciated the wonders of nature.

What are you doing to mark the start of fall?  It seems all our local osprey here in the Mid-Atlantic marked it by heading south!

What’s happening in your neck of the woods?



Glad to know this. I always wondered how plants and wildlife knew if was the fall season even though it is still quite hot in the south.

Posted by Vicki on 9/21

Location:  SE Wisconsin.

As late as last week, our chipmonks were active and then suddently, I haven’t seen any for the past 3 days.  Maybe they’ve settled in for a rest.

In years past, our chipmonks retired to their burrows by Sept. 12.  They are retiring about a week later this year.

Posted by JemDandy on 9/22

Thank you for the article on shorter days. We await the Juncos.

Posted by kelverl on 9/22

Squirrels are active scampering around. Common Green Darners are abundant and probably getting ready to migrate.
Yonkers , New York

Posted by Walter Chadwick on 9/22

i like to make sure i put out extra hummingbird juice, so they have a good start for there long trip south , also i grow sun flowers and i always leave some in the head , then i put wedge them up in my tree to give the birdies a treat , so far only seen nuthatches taken advantage of them :o)

Posted by John Tyson on 9/22

The yellow warblers have arrived in SE Louisiana!  I know fall is upon us when I see them flitting from tree to tree in my backyard.  Look forward to them each year. smile

Posted by Ava on 9/23

I’m located in inland San Diego County…wondering if I should be concerned since all of the Hooded Orioles that frequent our yard have long departed….except for one or two…I’ve only been seeing one on the hummingbird feeder the last few days….My thought was that is was a late fledgling…I’m worried about it, but my hubby sez that it will figure it out and head south just as it should…any thoughts out there? Thx!

Posted by marty on 9/24

a. animals have 5 senses (sight, smell, taste, hearing and touch), while plants do not. (they do react to touch, but do not have nerves, so they don’t feel it the same way). also plants have rectangular shaped cells, while animals have circular shaped cells. also the cells are much different from each other in the nuclei.
b. plants do not have mobility, animals do. plants can only grow towards light, while the roots grow smoothie recipe

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