MAX BLAKE (Deputy Zoological Director) writes: In the light of recent events, althought it seems probable that Rufus would not have been cured however early we caught the disease, Jon and I have decided to do monthly physical exams of all the wild birds in the collection. At the moment these are just the two corvids (both rescues): Ichabod the carrion crow, and Jerry the jackdaw.
We are funded largely by donation, and so it is CFZ Policy to publish our ongoing operations.
Oll and I started with the Carrion Crow (measured after he had had his morning food) because he is by far the tamest 'wild' bird we have, and we made these observations:
1. He was fairly calm during handling, but not when he was caught in the net. He nearly caught my fingers a few times!
2. He doesn’t try to escape by flying away from the net, but tries to run away. This could mean he's becoming tamer, or it could be because he is underweight.
3. Measuring the length (from the tip of the bill to the end of the short feathers at the end of the pygostyle (under the longer tail feathers)) showed that he was 27cm long.
4. Weighing him using the kitchen scales showed him to be 320g.
5. I could feel that there was muscle on the keel, but you could easily feel its edge and part of the bone on either side. The vet on Tuesday said that you should be able to feel the edge, but not much of the keel bone. This suggested that our crow was a little underweight.
Getting back to a computer, I looked up just how large a carrion crow should be. Looking on a number of websites, the average weight was 510g and 47cm long (total length). This suggested that our crow was either tiny, or very underweight. I scaled up the total length of our crow, and got a rough estimate that his total length should be 35cm. His actual length at the moment is smaller than this because he is missing some feathers and is generally a bit ratty around the edges. Doing some ratios, I worked out that your average crow weighed 10.85g/cm, but our crow (using the estimated total lengths) was 9.14g/cm. So, yes, he is a little underweight, but he is also a very small crow. Oll and I decided to double his food intake (starting today). He will be weighed again in a couple of weeks, and if his weight is over 380g I will be happy.
The jackdaw was next. Considering he is not an adult, he was expected to be smaller than the average bird. Catching him proved to be very hard, but the best technique was to move him toward the door side of the cage (with the door shut!), and lower him down onto the ground where he can be caught. He never seemed to want to bite, but he calmed down when he had my finger grasped in his feet. He was weighed at 200g and was 28cm long. I could feel the edge of the keel, but not very much of the side of the keel, which suggested that he was a good weight. We put him back and got back to the computer.
The average weight of a jackdaw was found to be 220g with a length of 34cm. Making a ratio, we get 6.47g/cm. Our jackdaw was found to be 7.14g/cm, so a little overweight. However, because he is still growing, I don’t think that we should try to reduce his weight yet. At his current length, he should be 182g. A more accurate scale may help in the future.