ajohn

Yes, definitely Savanna Nightjar. Your photo shows a female - note that the pale wing patches are buff rather than white and the outer tail feathers are not white.
Congratulations - they are difficult birds to see during the day time, and it is very unusual to find the nest.

Please do not provide any information to others about the exact nest location. The birds may be sensitive to human disturbance, and for a species nesting in the open the eggs could be in danger if they are left exposed to the sun. But do please try to remember to submit the record to the HKBWS so that we have a better knowledge of distribution and breeding behaviour of this species.

ajohn

Yes, it is normal for nightjars to nest in the open like this. The adult will normally spend the day shading the eggs from the hot sun (this is why I mentioned the dangers of keeping the birds away from the nest - it sounds like you did the right thing by only looking briefly at the nest, then moving away to a larger distance so that the birds could return). The most dangerous time for disturbance will be now, while there are eggs. The young should be able to move away from danger even when fairly young. The nesting should be finished long before October (the young will probably start flying in mid-summer), so I do not think this will interfere with your event.

You may be right that there is another bird in the top left of the picture, but I'm not sure whether this is actually the shadow on the rocks.

You can download the non-rare bird record form at:
http://www.hkbws.org.hk/web/eng/download_eng.htm
http://www.hkbws.org.hk/web/chi/download.htm

ajohn

Quote:

Original posted by butter at 2/06/2011 17:41

Do they give warning when people wander near? ... there're birds chirping but not when we're near the eggs.

Savanna Nightjar do give a fairly quiet 'chook' call when disturbed, they also have a call 'schooeep' which is used for display. If you heard the brids when they were away from the nest, they were probably trying to get your attention to make you follow them. Most predators would usually follow the adults, rather than thinking to look for the nest. Many birds use similar 'distraction displays'.

Quote:

Original posted by butter at 2/06/2011 17:41

How do the adults shade the eggs?

The same way as other birds - with their bodies. As the bird covers the eggs, it's body shields the sun and keeps the temperature right for incubation. Although the egg needs warmth to develop, the direct sun it so hot that an egg in the full sun would simply cook. It always amazes me how some birds are able to sit in the sun all day during the heat of the summer without suffering from heat stroke.