Marc,
Nice photos of the Pied-billed Grebes and their nests.
Below is some information on incubation from The Birds of North America account on pied-bills.

Check it out on-line at http://bna.birds.cornell.edu/bna<http://bna.birds.cornell.edu/bna>
Better yet, subscribe (one of the better deals for $ 40 a year), you'll have this information at your fingertips for all of North America's breeding birds.
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"Onset Of Broodiness And Incubation In Relation To Laying
After second egg, incubation gradually increases. Constant diurnal attention at or before 4-egg stage ( Otto 1983b<http://bna.birds.cornell.edu/bna/species/410/articles/species/410/biblio/bib130>, Forbes and Ankney 1988b<http://bna.birds.cornell.edu/bna/species/410/articles/species/410/biblio/bib065>, Muller 1995<http://bna.birds.cornell.edu/bna/species/410/articles/species/410/biblio/bib119>).

Incubation Period
Varies from 23 to 27 d (n = 32; Ackerman and Platter-Reiger 1979<http://bna.birds.cornell.edu/bna/species/410/articles/species/410/biblio/bib001>). Otto ( 1983b<http://bna.birds.cornell.edu/bna/species/410/articles/species/410/biblio/bib130>) marked eggs during laying phase and determined an incubation period of 20.5-27 d (mean 22.7 ? 1.1 SD, n = 120). From laying of first egg to hatching of first egg: mean 23 d ? 1.30 SD (range 21-26, n = 13; Forbes et al. 1989<http://bna.birds.cornell.edu/bna/species/410/articles/species/410/biblio/bib066>); 23.5 d (range 22-27, n = 22; Muller 1995<http://bna.birds.cornell.edu/bna/species/410/articles/species/410/biblio/bib119>). Position in laying sequence affects length of incubation. On average, eggs in fifth position have shortest incubation period ( Otto 1983b<http://bna.birds.cornell.edu/bna/species/410/articles/species/410/biblio/bib130>). Incubation of infertile eggs continues up to 57 d ( Muller 1995<http://bna.birds.cornell.edu/bna/species/410/articles/species/410/biblio/bib119>)."

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As far as taking pictures around hatching is concerned; a word of caution. Young emerge from the egg wet (obviously) and need to climb onto the attending (incubating or brooding) adult's back to dry off (about an hour). Small young will float but can become water-logged and drown, so look for signs of alarm in the adults. The adult in the fourth photograph on your web page is clearly alarmed by your presence / proximity. I trust you backed off and let it return to its nest.

On overcast days newly hatched young survival can be compromised by exposure due to absence of the adults.

The eggs in your second photograph look fresh to me. After a week of incubation they usually take on brown coloration.

Heat from rotting plant material used in the nest provides some heat for incubation. Covering the eggs with plant material during the adult's absence probably has more to do with temperature regulation than camouflage, since in my experience the adults leave new eggs (prior to onset of incubation) exposed. If camouflage were the objective then why would they leave the fresh (mostly white) eggs uncovered, and cover the eggs as during the later stages of incubation when they are stained brown?

There are locations where pied-bills are quite used to large (and I mean large) amounts of foot traffic, near their nests. For instance on Green Lake, where I made the majority of my observations, some nests are within 30 feet of shore. I watched eggs hatch there, and with a good telephoto lens one can take pictures with a high 'cuteness' factor without risk of adversely impacting the subject.

Good luck on your project.

Martin Muller, Seattle, WA

martinmuller at msn.com