Saturday morning started off with clear skies and bright sun, with a bit of haze.  During the morning the skies turned partly cloudy and then completely overcast.  The wind started out from the north at 8MPH, and then shifted around to the east, but remained around the same speed until picking up speed late in the day.  The temp hovered around 50F most of the day.

The peregrines spent most of the day in incubation mode.  Some times, you have to watch for quite a while until you observe a break in the action!  It is fascinating to watch how careful they are when hovering over and then settling onto the eggs.  Frequently, you will be able to watch a nervous twitching and jiggling around until the incubating bird gets it just right.

According to Derek Ratcliffe, the eggs of the peregrine falcon are among the most handsome laid by any species of bird!  He notes that the prevailing color is reddish-brown with a wide variation.  The surface of the fresh egg has variable amounts of bright red-brown markings appearing as a freckled, mottled, or blotched layer which can easily be rubbed off when the shell is wet. This non-fast layer of pigment gives a peregrine egg much of its beauty and richness, and in fresh specimens is often accompanies by a kind of bloom!

Literature cited: Ratcliffe, D. 1993. The Peregrine Falcon. 2nd ed. Carlton, England: T. and A. D. Poyser.

Onset Of Broodiness And Incubation In Relation To Laying

Here is a look around 6:30 AM this morning, under clear skies, winds from the west at 8MPH, and temps in the low fifties. It looks like we have officially started full time incubation. In temperate latitudes, full time incubation usually begins with the penultimate, or second to last egg egg.  When temperatures are at or near freezing, active incubation may start a bit earlier. We have now seen either the female or the male incubating the eggs with almost no break in between shifts, since the fourth egg was laid.  The male seems to be taking a very active role in the incubation process.

Incubation Patches

Both sexes have paired lateral brood patches. Less well developed in male. Belly area may function as patch also but less edematous and vascular than breast (TJC).  In this photo, the male is taking a break on outside edge of the nest box.  He waited a while until the female showed up and set down on the perch pole outside the nest box.

Incubation Period

The peregrines at this location have usually incubated their eggs for 29 to 33 days. In the early days of brooding it’s important to keep the eggs as close to their ideal incubating temperature as possible. If it is too hot or too cool and the eggs won’t develop properly. Later in the incubation process, proper temperature isn’t quite as important.  After a couple of weeks the falcons will be able to leave the eggs uncovered for longer periods of time.  Sometimes leaving the eggs uncovered frequently, or for long periods can mean that the eggs hatch a few days later than normal. This is a very well protected nest box in a location where the resident peregrines will not be disturbed, so they will tend to incubate steadily until the eggs hatch.

Literature cited:

White, C. M., N. J. Clum, T. J. Cade and W. G. Hunt. 2002. Peregrine Falcon (Falco peregrinus), version 2.0. In The Birds of North America (A. F. Poole and F. B. Gill, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bna.660