2002 season
LIST OF PAGES
Nest building
Initial egg-laying pictures
Second egg-laying pictures
Feeding while brooding
More brooding pictures
Hatching pictures
Defence pictures
Epitaph
A truly excellent site about these birds
Visitors since 10th September 1999:
What does a mother bird do during the long tedious hours spent incubating her eggs?
Well, for certain she doesn't spend the time asleep. There is much activity of turning the eggs, rattling them, moving nesting materials around, shaking backwards and forwards and sideways, standing on her head, and indulging in exotic contortions. To start with we show her sitting comfortably and statically, slightly fluffed to preserve the heat, and listening to the world outside. The rain lashes on the top of the nestbox, which attracts her attention.
At intervals she departs, to return with more nest materials or a full tummy of food, showing the eleven eggs, objects of her attention, lying in a circular well of nest materials. It seems that the object of digging this well is to confine them underneath her and to stop them rolling out sideways when she is indulging in acrobatics. Here are the eleven eggs during a five minute absence.
When she returns, she is accompanied by her mate. He scrabbles about on the outside of the box, and she opens her beak wide like a young chick, asking to be fed. After a bit he departs. No food is forthcoming yet; perhaps this happens later on, as they will have a hectic feeding time when the eggs hatch. Here is a picture showing her open beak, and his beak visible in the entrance. Curious sounds are made by both of them.
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).
After two days of brooding, we have only had two brief glimpses of the male bird. The weather has warmed up over the last two days. Our bird comes and goes sporadically to feed herself and to bring more nesting materials into the box. She spends much time shuffling the eggs around. The absences can be as long as three hours in the morning, but later in the day are rarely longer than ten minutes. We have now acquired about 22 hours of videotape recordings; the sound track on these consists of birdsong interspersed with the thunder of jets passing over from Heathrow Airport, which is 17 miles away. The nestbox with its entrance hole forms an excellent Helmholtz resonator and the tape soundtrack frequently saturates with the noise of these aircraft, which do not sound particularly loud outside. Our bird listens intently to the other noises in the garden, responding to the birdsong with her own tweeting, but apparently unperturbed by the aircraft and the noises made by piano playing indoors, and the sliding of the patio doors just underneath the nestbox.
It is said that these birds provide good hosts for fleas, such that one has to be careful when cleaning out the box at the end of the season not to get bitten. Our bird frequently wakes suddenly and scratches her body under the wings with her beak, preening, and obviously seeking something in the feathers.
The bird has also been seen to scratch herself vigorously with a foot.
There are frequent comings and goings. The arrivals are unheralded and at high speed. Here are a couple of action shots of an arrival.
Departure requires a heave up from the nest depression, and then a little jump, sometimes assisted by a few wing flaps.
There are occasionally energetic acrobatics in the nest. It is not clear why. The eggs are not always treated gently, and sometimes her wings are brought into play to bat the nest materials down, as in the picture below.
Frequently the bird shakes from side to side, making a rattling noise with the eggs, which can be seen to change their positions between absences of the bird. She has a remarkably constant respiration rate of about 120-130 breaths per minute; it is noticeable that the breathing becomes heavier at times (but not quicker), possibly to generate more heat for the egg-warming. She has made a deep nest now and is trying to snuggle down into the materials so that only her back is exposed to the cold air.
The method we have used of taking screen pictures with the Mavica digital camera has not been very successful. There is aliasing between the timebases in the camera and the monitor, which puts dark bands across the pictures about 7 out of 8 times, necessitating repeated shots to get an acceptable picture. Also, the shadow mask tube produces visible stripes and dots, particularly in close-up shots of the screen.
Accordingly, we have ordered a new item of video capture electronics which is expected to arrive on Monday 26th April. This should result in better pictures than the ones posted so far, some of which may get replaced with retakes in the next 7 days.