Monday, October 4, 2010

Reverse photoperiod and fall fun

Photoperiod refers to day length (length of both light and dark periods), and it causes significant physiological responses in plants and animals. Photoperiod dictates the onset of animals' sleep, migration, reproduction, and the changing of coats or plumage. Day length signals seasonal changes in many species, and is the first cue to change fur color in snowshoe hares and it even induces estrus in many mammals. Some plants will flower only after experiencing a certain photoperiod for a certain number of days. Yet despite how intricately timed this mechanism is in animals and plants, there can be confusion. Just as a broken clock is right twice a day, the photoperiod is identical twice a year. Anyone that has spent time in the woods knows the tricks that this phenomenon will play on animals.

For example, in the fall the day length is the same as the spring (and vice versa). This is why you hear ruffed grouse drumming in the fall, as though it were the spring. In our garden, northern flickers are making their mating calls and even displaying their courtship rituals, chickadees are making their lovey-dovey pleas for a cheeseburger, and nuthatches are playing their tiny tin horns (maybe this is why the Bike Gardener thinks she is hearing nuthatches today, or maybe it is a personal thing). Many spring nesting species are checking out nest boxes. Reverse photoperiod even fools plants. Many plants that flower in the spring will also flower in the fall, like the erigerons in this post.
Reverse photo period may also partially explain a fall migration of the largescale suckers in the Clark Fork River, but I digress (their spawning migration is in the spring).

If nothing else, it is fun to say that things, often totally unrelated things, are a result of reverse photoperiodism. Give it a try in conversation this week and impress your friends.


  1. Except that my nuthatches ank ank all winter long...I think they are saying that they are happy to be back in the land of milk and honey. ;-)

  2. Your post explains Photo period very well, even good to understand by inexperienced gardeners.
    I live in SE Texas and yes, there are some of my plants flowering in the Spring time and then once again in the Fall season. Now I'm not sure if that is only because of the photo period or mainly because it is so hot here during the summer.

  3. You know I thought that they rebloom in Fall just to take advantage of the weather! This was very interesting!