bird: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/sbin/bird - from package: bird

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/sbin/bird - from package: bird-bgp
/usr/sbin/bird - from package: bird

You may install the required package with command apt-get install {package}

Error in other languages:
bird: bevel nie gevind nie
bird: comandă negăsită
bird: comando não encontrado
bird: commande introuvable
bird: command not found
bird: käsku ei ole
bird: không tìm thấy lệnh
bird: komanda nerasta
bird: Kommando nicht gefunden.
bird: kommandot finns inte
bird: komut yok
bird: nie znaleziono polecenia
bird: níor aimsíodh an t-ordú
bird: no se encontró la orden
bird: no s'ha trobat l'ordre
bird: opdracht niet gevonden
bird: parancs nem található
bird: perintah tidak ditemukan
bird: príkaz nenájdený
bird: příkaz nenalezen
bird: команда не найдена
bird: командата не е открита
bird: 命令找不到
bird: コマンドが見つかりません