Why does the system ban chicken but allow pigeon, when both are birds?
Chicken vs pigeon
What the system says
The system ties the chicken ban to two claims: industrial farming practices (growth hormones, antibiotics) that differ from the bird's nature, and a claim of "digestive difficulty." Pigeon, being a smaller bird typically raised traditionally, gets grouped with quail among the permitted wild-style birds.
What science says
Scientifically: cooked chicken is among the most efficient and bioavailable protein sources, with no scientific support for the "hard to digest" claim. Growth hormones in poultry are legally banned in many countries. Concerns about industrial quality don't justify a blanket chicken ban. Pigeon is good meat but more expensive and less available.
If you stick with the system, pigeon, quail, and rabbit are excellent alternatives. If you're not strict, well-cooked chicken (from a trusted source where possible) is a healthy and accessible option.