Thursday 8 June 2017

BirdBox2017: end of another season

It's been a very successful year for our blue tits, great tits and our two Raspberry Pi powered bird boxes.

The last of our bird box chicks left the safety of their nest yesterday, and so ends another season for us.

Out of 15 eggs in two boxes, 14 chicks got the chance to explore the world outside and potentially become food for sparrowhawk chicks or maybe the short-term plaything for one of the local cats.

Despite having 4 suitable tit boxes, and a close neighbouring garden having one more, the only nesting tits chose our two camera equipped boxes.

And now we have the pleasure of watching the inexperienced juveniles around our bird feeders, picking fights with other birds, and frequently getting beaten up as a consequence.

the blue tits

The adult male did a great job keeping others tits (blue, coal & great tits) out of our garden and deterring others from setting up home in his patch. At least he did until a more determined great tit rocked up with his misses.

I didn't witness any confrontations between the two males, but just after the great tits established themselves in the second box, I noticed the blue tit male's head feathers looking rather "dishevelled". This may have been a coincidence, and could be due to a parasite. Either way, it made identification easier, both inside and outside the box. I now notice that he has developed a lump or growth on his head, so suspect his days are numbered.

The blue tits chose our 28mm hole box which faces east and is mounted about 2m off the ground on the side of our pergola.

The female laid 9 eggs fairly late in April and they started to hatch on 4th May. Because of the "narrow top" nature of the nest, I could not accurately count the chicks, so was not sure whether all had hatched. But once the sides of the nest cup were trampled down by the growing chicks, it was clear that we had 8, so one was missing.

Having now examined the nest, I cant find an unhatched egg, so I think #9 did hatch but died in the first few days and was removed from the box. However, 8 out of 9 is not too shabby!

After leaving the nest the chicks remained concealed in the trees and bushes at the bottom of our garden for a few days. They now arrive at our bird feeders as a family group, but are even more difficult to count, because while some are on the fat balls, others are on the peanuts or sunflower hearts, or just in among the branches of the apple tree which is the host for our hanging feeders. I suspect 2 or 3 have already been lost to predation.

the great tits

Our great tit pair seemed to arrive very late and only laid 6 eggs. Birds are individuals, so it may have just been part of the natural spread of behaviour. However, I couldn't help wondering whether they had started nesting somewhere else and may have been disturbed, before settling down in our garden.

They chose our 32mm hole box which is mounted 3m up a Canadian Maple tree, and faces north (ish).

They created a nice cup shaped nest which made counting eggs and chicks so much easier than the blue tits. However, as the leaves opened up on the maple, they tended to block the light from the single, east facing window on the box, making photography rather more difficult.

an adult tries to encourage the last two great tits out of the box

All 6 eggs hatched and all six chicks left the nest within an hour yesterday morning. I haven't seen any of them in the garden so far, but would expect them to start visiting the feeders by the weekend.

one last look

In previous years I've noticed that after all chicks have left the nest, parents return to the nest, have a look around and then leave. This year I locked both systems on after the last chicks had left. I then noticed that adults would return 2 (great tit) or 3 (blue tit) times, sometimes clearly bringing in food.

The question is why do they do that?

If there were only two visits within (say) 30 minutes of the last chick leaving, you could argue that each parent was unaware that all chicks had left. But in the case of the blue tits, all 3 visits were made by the female, and the last was about 2 hours later.

Is it because they have a poor memory? That would seem very unlikely.

Maybe chicks sometimes get back into the nest for safety? This would make some sense if this was a common event, and "evolution" had determined that parents that re-check the nest are more successful at passing on their genes.

Maybe its just a habit (after all, they have made thousands of visits in the last few weeks) but I've never noticed birds returning to a monitored bird box in the days and weeks that follow, its only for an hour or two following evacuation.

the 32mm hole box system

This system (as used by the great tits this year) is virtually unchanged from the original designed and built in the winter of 2013/14. It uses an NE555 timer chip to control power to the Raspberry Pi model A and RaspiCam camera, based upon activity at the box enterance. The battery monitor is simply a run-time timer based upon an assumed average supply current (i.e. I assume the 12AHr battery will have a life between charging of 50 hours).

No one is more amazed than me that this system has worked so well every season for the last 4 years.

I was tempted this year to rebuild the system using a Pi Zero, but if it ain't broke....

the 28mm hole box system

I think this is the first year that this system has played host to a successful nesting family. Originally designed and built during the winter of 2014/15, this system uses an 8pin Picaxe in place of the NE555 timer used in the earlier system. The Picaxe not only controls power to the Pi and camera, but also measures the battery voltage. This is a better approach than using a run-time timer because as my lead/acid batteries age, so the capacity falls.

For this season I replaced the original Pi model A+ with a Pi zero and added an external camera. The Pi Zero is a better choice than the A/A+ because it has better performance. The main benefit to this is when performing maintenance, where a number of programs are run (e.g. the box software, VNC, file managers & so on) or when running the Gambas IDE to modify the main box code.

Unfortunately powering two camera systems (the internal and external) from the same battery almost halved the run-time between battery recharge. The result was a 35-40hr run-time, which was too short and quite annoying. If I use this system again I will incorporate some way of selective powering (e.g. I'd probably control the power to the external camera from the internal camera interface).


I always thought that when I finally fully retired (as I did last year) I'd have more time to observe activity in our bird boxes. I have to confess that this hasn't happened. I always seem to have things to do, so the boxes have not had the attention they deserve.

Not only have we spent less time "watching" this year than in previous years, but I have also forgotten to remove video files quickly enough, resulting in the inability of the systems to run properly, and the need for me to "SSH" into the system to recover the situation.

I think I may have lost enthusiasm for this, so may give-it-a-miss next year, unless I can think of a technical challenge to re-ignite my enthusiasm, or I can deploy a permanent POE type bird box installation.

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