sparrow?

I though that this is a sparrow but the yellowish color confused my

thoughts. This photograph was taken with a 600 mm Sigma Reflex lens.

The donut shaped bokeh is the mean characteristics of reflex lenses.

It has an f value of fixed 8, that makes it hard to focus especially

in low light conditions. The shallow depth of field in close objects

(this lens can go as close as 2 m)produces a beautiful effect on

background. I did not understand the blue shift of the background

color as the white bakance was in auto mode and I did not see it

before. Thanks for your critics and I should be glad to learn if you

have experiences with reflex lenses on DSLR.