Changes

The '''cere''' is situated at the base of the upper beak and is composed of keratinised skin. The colour of the cere is influenced by diet and hormones.

The '''cere''' is situated at the base of the upper beak and is composed of keratinised skin. The colour of the cere is influenced by diet and hormones.

The beak has two holes called '''nares''' (nostrils) which connect to the hollow inner beak and thence to the [[Cardiorespiratory System - Anatomy & Physiology|respiratory system]]. The nares are usually located on the dorsal beak. In some birds, they are located at the base of the beak in the '''cere'''.

The beak has two holes called '''nares''' (nostrils) which connect to the hollow inner beak and thence to the [[Cardiorespiratory System Overview - Anatomy & Physiology|respiratory system]]. The nares are usually located on the dorsal beak. In some birds, they are located at the base of the beak in the '''cere'''.

In some species of bird, the tip of the beak is hard, dead tissue used for heavy-duty tasks such as cracking nuts or killing prey.  In other species of bird, such as ducks, the tip of the bill is sensitive and contains nerves, for locating things by touch.  The beak is worn down by use, so it grows continuously throughout the bird's life.

In some species of bird, the tip of the beak is hard, dead tissue used for heavy-duty tasks such as cracking nuts or killing prey.  In other species of bird, such as ducks, the tip of the bill is sensitive and contains nerves, for locating things by touch.  The beak is worn down by use, so it grows continuously throughout the bird's life.