Autumnal Recrudescence––Say What???

Happy Autumnal Equinox!
But, curiously it feels like Spring again. Why? Because I’m awakened by the birds in our neighborhood at dawn, singing as if it’s June.

Perhaps you’ve noticed it too. So what physiological reason can we attribute this to?  It’s due to a phenomenon with a hard to pronounce name – autumnal recrudescence.

The theory about autumnal recrudescence is this: Some sex hormones are triggered to be released based on the hours of daylight, and certain hormones “inspire” a bird to sing. At some point, when the daylight hours of autumn match those of just the right time in spring, those hormones are re-triggered and drive some birds to sing for a short period in the fall.

In other words, when Fall days are roughly as long as the days of the Spring mating season, birds experience a hormonal surge that triggers singing by males, despite the fact that they will not be breeding for many months.


Anna’s Hummingbird by Stephen Shunk


The poem below, written by Susan Stiles in 1973 poetically sums up the phenomenon:

The Autumnal Recrudescence of the Amatory Urge

When the birds are cacaphonic in the trees and on the verge

Of the fields in mid-October when the cold is like a scourge.


It is not delight in winter that makes feathered voices surge,

But autumnal recrudescence of the amatory urge.


When the frost is on the pumpkin and when leaf and branch diverge,

Birds with hormones reawakened sing a paean, not a dirge.

What’s the reason for their warbling? Why on earth this late-year splurge?

The autumnal recrudescence of the amatory urge.

-Written by Susan Stiles, copyright December 1973


  • An excellent book that describes autumnal recrudescence, and many other topics in bird biology and ecology, is The Birder’s Handbook by Paul Ehrlich, David Dobkin, and Darryl Wheye.


More Bird Resources on this Website

Here are some more stories, videos, and bird sketching resources I’ve written.

World Penguin Day

All About Whooping Cranes

How to Sketch Barn Owls

World Migratory Bird Day and Why Birds Migrate

My Costa Rica Birding Big (sketching) Day

Tips for Sketching Birds

How to Sketch Kestrels

Celebrate Vultures

How to Draw Hummingbirds

Identifying Warblers in the Spring

The American Dipper

How to Sketch Parrots

Autumnal Recrudescence

How to Draw Bluebirds

A Black-headed Grosbeak Nest (video)

Kid’s Bird Coloring Pages

Blue-winged Warbler


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