Need a cheap way to weigh birds


Thread Starter


So I have 20 wild-caught birds that are being used in a series of lab experiments involving stress hormones, feeding rates, and whatever else my boss can think of. We want to be able to monitor each birds' weight without having to handle them, which induces unwanted stress. So it would be nice to have some sort of scale attached to a perch, perhaps hanging down from the top of the cage, that could be used to log a bird's mass. So I'm looking for some means of building 20 simple scales that can give a voltage or resistance output that corresponds to the weight of the bird on the scale. I have the software and interfacing equipment for translating resistance or voltage into weights. All I need are sensors. The birds weigh only 70 to 100 grams, and the perch would probably add another 100 grams. I need accuracy to 1 or 2 grams. The size and shspr of the load cell doesn't really matter as long as there is some way to hang a perch from it. I've found some things that are close to fitting the bill, but aren't perfect. I bought a small electronic pocket scale a few months ago for about $20. What sort of load cell might it have.

Tomy Zacharia

Dear Eli,

If "electronic surveillance" is not required, then the perches can be hooked up to say 0-200 gm spring balances. The cost involved would be trivial and as the number of birds is only twenty, it might take 15 mins to take measurement of all the birds and note it down. Now if the birds refuse to be on the perch when you are ready to take the measurement, then it is a problem.


Tomy Zacharia
Hey Tomy. That is exactly the problem. The birds more or less go nuts when someone is in the room, so there is no way a bouncy spring balance will give a good reading. The birds seem to settle down when no one is in there, and we've thought about setting up a video camera to monitor spring scales. However, I don't think the birds would like a bouncing perch, and a good spring scale is about $35. So that's why we want some cheap but fairly accurate pressure sensors.
Techniques for measuring weight use load cells, which incorporate a strain gauge, which measures minute deflection of the base or whatever it is that the strain gauge is bonded to.

Pressure is a measurement of force per area unit (pounds per square inch) so pressure sensors aren't really the right approach.

If $35 per measuring point is steep for this project, I doubt there's a commercial solution.

But, years ago, one could buy tiny strain gauges and bond (glue) them to a base. Proably still can.

The strain gauge needs electrical excitation (a dc voltage) and its output is proportional to the deflection caused by the force upon it.

Why don't you google "strain gauge" and see what you come up with?
If a $35 expense is unbearable you should abandon all hope with regard to load cells - the expense is orders of magnitude higher. You can probably rig up a set of strain gages on your perch suspension but there is an art to bonding them and you will have to be aware of temperature effects.

I suggest that you select a vendor and work with him on how to mount the gage. To help deal with the temp effects, consider automatically taring the gage each time the perch is unoccupied. ISA's web site lists candidate vendors:

Curt Wuollet

Or you could put the whole cage on cheap postage scale type sensors and monitor the rapid changes in weight. Cage with bird on floor or perch - cage with bird in air = bird.

Thanks for all these suggestions. I know that load cells generally cost hundreds and are out of the picture. I was hoping there was something out there similar to what is incoporated into inexpensive electronic scales. The idea of weighing the entire cage is interesting, except the cages weigh about 8 kg and the birds about 80 g. So I doubt the resolution would be good enough to detect small changes in bird weight.

I'm going to see if the Tekscan Flexiforce sensors will work. I'll run my idea by one of their reps and see what they say.
Hi Eli,

Load cell works on strain gauge principle which is not a good way, but how about a balanced wheet-stone bridge arrangement. Cheap and easily available and may be perfect for linearity and resolution issues.

hope it might give some idea.

you could use phidget sensors/boards. for 20 weight sensors, you'd need (3)8/8/8 boards (each w/8 analog inputs):

you'd need 20 force sensors:

and you'd need to mount them under the contact point of each perch mount, so the force is squeezing the sensor.

if the birds could be over 3kg (6.6lb), you could "roll your own" force sensors with force sensing resistors:

this may be over your budget though, at $240 for the boards + $220 for the sensors & cables (or $130 for the FSR's), or about $19-23 per perch.
I have been looking for a sensor simular to your needs and am doing some checking on the following site. Give it a try. If you come up with something simular at a good price and availability please give me a shout. Thanks [email protected] --
You can connect the strain gauge to a low cost DAQ module (US$79) that has gain and differential inputs. You need to have a computer nearby though (chances are you may have). Good thing about the PC based solution you can write your own algorithm to figure out what is the weight. You can find the strain gauge app note here: