Thylacine
master brummie
Radiorails, I've never heard of a chook being named after a bus before. But it works for me! 
O 8209 was one of a batch of thirteen Tilling-Stevens TTA1 30 hp petrol-electric double deckers (registered O 8200-8212), new to Midland Red in May 1912 with Brush O18/16RO bodies. Under the "Birmingham Agreement" they all passed to the Corporation in October 1914. As Lloyd has explained, they were seriously underpowered as double deckers. Seven of them (O 8200-8206) were withdrawn in 1916, the other six being rebodied in that year as rear entrance single deckers. Five of the new bodies were also by Brush. These six remained in service until 1919.
O 8209 was special. Its chassis number (2) was the lowest of the batch (as far as is known). So it may well have been strictly the "oldest" BCT bus when acquired in 1914, as your friend suspected. The single deck body acquired in 1916 was by Dodson rather than Brush for some reason. And it had a life after withdrawal from service in 1919: it was re-seated to B14R in 1921 for the exclusive use of the Birmingham City Transport Committee.
I am aware of three pictures of these TTA1s:
[Does anyone know of a picture of "chook bus" O 8209? Since it lasted longer than the others, you would think that someone photographed it.]

O 8209 was one of a batch of thirteen Tilling-Stevens TTA1 30 hp petrol-electric double deckers (registered O 8200-8212), new to Midland Red in May 1912 with Brush O18/16RO bodies. Under the "Birmingham Agreement" they all passed to the Corporation in October 1914. As Lloyd has explained, they were seriously underpowered as double deckers. Seven of them (O 8200-8206) were withdrawn in 1916, the other six being rebodied in that year as rear entrance single deckers. Five of the new bodies were also by Brush. These six remained in service until 1919.
O 8209 was special. Its chassis number (2) was the lowest of the batch (as far as is known). So it may well have been strictly the "oldest" BCT bus when acquired in 1914, as your friend suspected. The single deck body acquired in 1916 was by Dodson rather than Brush for some reason. And it had a life after withdrawal from service in 1919: it was re-seated to B14R in 1921 for the exclusive use of the Birmingham City Transport Committee.
I am aware of three pictures of these TTA1s:
[Does anyone know of a picture of "chook bus" O 8209? Since it lasted longer than the others, you would think that someone photographed it.]