LIST OF PAGES
Nest building
Initial egg-laying pictures
Brooding pictures
Feeding while brooding
More brooding pictures
Hatching pictures
Defence pictures
Epitaph
A truly excellent site about these birds
Visitors since 27th September 2000:
...The adage has it, "more is not necessarily better"....
Periodically, the bird turns her eggs. This involves a certain amount of hard physical effort, mostly upside-down. Possibly the eggs are turned to even out the pressure or temperature. It is also said that humidity regulation is important; this may be one of the reasons for the feathers.
Occasionally the bird over-balances, giving a fine view of her egg-laying parts.
The bird gets up just before dawn and disappears into the garden for 10-20 minutes. When she comes back, she sits intently for some minutes, with the occasional visible contraction, presumably laying the egg of the day.
When she is finished, she looks around inquisitively and listens again to the world outside. Is this an expression of contentment? What does it feel like to lay an egg? Who can tell us?
Shortly afterwards the bird departs for the day, only revisiting for the briefest of visits to bring more feathers. We are lucky to see as many of the 8 eggs as this, considering the number of mobile feathers in the nest. Occasionally, even the bird is partially obscured by a miasma of feathers.
Later in the day, more feathers arrive. A visitor is admiring the feather-bearing bird on one such visit, when the bird suddenly has an inkling that "big brother" might be watching, so she climbs up the box and gives several sharp taps to the plastic cover over the camera lens. The lens, not unexpectedly, has trouble focusing this close...
A day later, nine eggs are visible. The second layer is starting. HCP?
On the morning of Tuesday 20th April 1999, the final (eleventh) egg was laid and the bird moved in to brood at about lunchtime on Wednesday 21st April, having industriously collected lots more nesting materials. The male partner appeared briefly at the entrance, conducting a conversation and flashing its beak through the opening. The hatching we anticipate will happen three days either side of 4th May 1999.
The eleven eggs are sitting on a 1cm thick piece of wood, and occupy an area 4cm by 4cm. At present the average outside temperature is 10C and we can assume that the eggs are at bird temperature, assumed to be 35C. The thermal conductivity of wood is about 0.002 watts per square cm per (degree C/cm) so the power flow out of the bird through the base of the nest-box, via the eggs, is about 600mW say plus or minus 50% on this estimate...
The energy content of peanuts is 164 kilocalories per ounce, or about 15,000 Joules per peanut. If half of this energy is available to provide for heat flow down through the eggs, then we need 2160 Joules per hour for the bird to keep the eggs warm, which is at least 7 peanuts a day.
So the male bird has to provide, daily, food for the sitting bird equivalent to at least seven peanuts to provide for her energy needs in keeping the eggs warm. This is about 40% of the bird's weight a day in peanuts, or 12kCal every 24 hours, or about 2/3 of a teaspoonful of sugar.
So, how much does a parus caeruleus weigh? 9-10 grams according to the "Complete book of British Birds" (AA/RSPB). Now I weigh 100 kg or 10,000 times as much, so if I ate proportionally I would have to consume about 70,000 peanuts or 30 one-kg bags of sugar a day.
We learn from this calculation how much more important energy balance is if you are a very small animal (or bird).