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San Francisco Nest Diary 2013:

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San Francisco May 9: For almost 3 months, this is the scene falcon-watchers have been observing on the camera--an incubating falcon. Now the second clutch of eggs (six total in the nestbox) has gone beyond the possible hatch window. Soon, we will collect the eggs and deliver them to colleagues who study emerging organic contaminants among sentinel species.

April 29: It is hatch week. Three eggs contributed by the former resident female, "Lil," did not hatch due to extended periods without incubation. Three additional eggs contributed by Cher have now had about 33 days of incubation. If fertile, they should hatch this week. Since hard incubation began immediately upon laying the eggs will hatch sequentially.

April 4: Cher laid a 3rd egg today bringing the total in the nest to 6 (3 are hers and 3 were laid by Lil and will not hatch due to long periods of non-incubation after Lil disappeared). The clutch of six eggs is receiving constant incubation. After Cher contributed an egg to the clutch she became a dependable participant in incubation.

April 1: The new female, known as "Cher" added an egg of her own to the 3-egg clutch on March 29. The new egg was added to the three-egg clutch laid more than a month ago by the prior resident female, "Lil." Dan and Cher are incubating the 4-egg clutch.

March 21: Dan continues to do all of the incubation. The new female, known as Cher, has assumed an incubation posture on a few occasions but leaves the clutch of eggs sprawled in the nest indicating that she is not getting it quite right. Lapses in incubation of one to four hours have been recorded by volunteer observers in recent days putting into question the viability of the eggs. Based on the dates of laying, hatching is anticipated by March 27.

March 14, 2013: About one week ago, Diamond Lil disappeared. We do not know her current status, just that she has not returned to the nest ledge. A new female, dubbed "Cher," has been visiting the nest ledge but does not seem  inclined to share in incubation duties. Dan has been doing all the incubation but he must also hunt for food to eat. The eggs have been uncovered during these absences and incubation has been uneven. The eggs need about 12 days more incubation. Will the eggs hatch? Will Dan continue to make a heroic effort at incubation? Will the new pair recycle and lay a new set of eggs? We will soon know.

March 4, 2013: Incubation is underway for a full set of 4 eggs. We should be able to see signs of hatching by March 26. Hatching is difficult to discern because the female will continue to stay on the nest almost full time for at least one week after hatching except to feed the young.

February 20: The third egg arrived today and with it hard incubation is likely to begin. Hard incubation, or the period when eggs are brought up to incubation temperature ~ 99 degrees fahrenheit, and kept there until hatching, generally begins with the arrival of the third egg. Some speculate that the sensation of having three eggs in the nest stimulates the falcon to incubate. The arrival of the fourth egg about two days after hard incubation begins means that it will hatch a day or so after the other three. If food is scarce the fourth hatchling will soon perish. Incubation takes about 33 days.

February 18: Egg two arrived today. The five days that have lapsed since egg number one have had us wondering. Lil was disturbed by workers on an adjacent roof when it looked like she was about to lay egg number two. The timing is right for the egg laid this morning to be egg number three. Egg number two may have been laid elsewhere when in the midst of nesting territory defense. We will never know for sure. In any event, it is nice to have a second egg in the scrape!

February 13: The first egg arrived today on the 33rd floor of the PG&E building. Eggs will arrive approximately every 56 hours until a clutch of four eggs is complete. Incubation typically begins with the third egg.