At the Pitt peregrine nest, E2 is sometimes so eager to incubate the eggs that he won’t get up when Dorothy arrives to relieve him.
If E2 is stays put and Dorothy’s not in a hurry she’ll wait as much as 15 minutes. Last year she fell asleep while she was waiting!
To get him moving she “talks” and walks around him. If he’s really stubborn she pokes him with her beak.
@PittPeregrines created videos of this parental bargaining using the webcam snapshots: Stubborn E2, above, and Nest Exchanges, below. E2 doesn’t dare to poke Dorothy but he’s persistent about taking his turn.
In a week or so Dorothy will take command and hardly allow E2 any time on the eggs. That’s because she’s in charge of hatching, expected around Earth Day. Visit the Pittsburgh Falconuts Facebook page to vote on the day you think the eggs will hatch.
How do birds instantly switch gears from the frantic activity of courtship to sitting on eggs all the time?
They’re cued by hormones. Here’s how:
As day length increases after the winter solstice, a bird’s hypothalamus releases LHRH (luteinizing hormone releasing hormone).
LHRH triggers the pituitary gland to release LH (luteinizing hormone).
LH increases production of testosterone in males and progesterone in females.
Testosterone triggers aggression, territoriality and sexual behavior. It’s good at the start of breeding but doesn’t help raise a family.
Progesterone is the “pregnancy hormone” that induces egg production. It’s only needed for a short time since female birds are only ovulating and pregnant until they lay the eggs.
On the day before incubation begins the hormones switch. Prolactin, the hormone that promotes incubation behavior, rises sharply while the other hormones suddenly decrease. In females, LH and progesterone drop off. In males, testosterone has been dropping since egg laying began. If the male shares incubation he has a sharp rise in prolactin, too. On a graph this hormone switch looks like a sine curve. There’s a moment where all these hormones are low, then prolactin takes off.
In peregrines, both parents have to be ready to incubate at the same time. Their courtship rituals help get the couples’ hormones in synch.
This whole process may sound as if birds are at the mercy of their hormones but in every species reproduction is chemically tuned for success. In humans for instance, progesterone and prolactin switch after delivery so that the mother’s body produces milk to feed the baby. Individual animals whose hormones malfunction do not have live offspring.
So how do birds incubate so nicely? In a word, prolactin.
(photo of Dorothy and E2 from the National Aviary falconcam at the University of Pittsburgh. Today’s Tenth Page is inspired by page 448 of Ornithology by Frank B. Gill.)
Spring is moving north and so are the robins. This week a big wave arrived after Monday’s snow. Now that they’re here, how soon will they nest?
Robins nest later the further north you go. In 1974 Frances James and Hank Shugart were curious about the conditions that governed their nesting times throughout the U.S. Using climate data and Cornell nest watch information from 8,544 robins’ nests they developed a model that predicted when robins would nest in a particular region.(*)
The model shows that robins cue on weather. Hatching is timed to occur when local humidity is 50% and temperatures are between 45 and 65 degrees Fahrenheit. By April 23, Pittsburgh’s highs and lows are exactly in that range so our birds are getting ready. Here’s what they’re up to:
Robins spend 5-7 days building their first nest of the season.
Egg laying begins 3-4 days after first nest completion.
Eggs are laid one per day for a clutch of 3-4 eggs.
Incubation lasts 12-14 days.
From nest building to hatching, the first nest takes 26 days. (Subsequent nests take less time.)
Our robins should be nest building right now except for one thing: Do they have enough mud to begin construction? Has the mud been frozen?
Watch the robins in your neighborhood to see what stage they’re in. Join Cornell Lab’s Nest Watch program and your data can become the basis for studies like James’ and Shugart’s that broaden our knowledge of birds.
(Credits: photo by William Majoros on Wikimedia Commons. Click on the image to see the original.
Today’s Tenth Page is inspired by page 260 of Ornithology by Frank B. Gill, portions of which are quoted(*) in this article.)