The plume/hackle is generally made from clipped chicken feathers and is worn on a military headdress purely for decorative or ornamental purposes. The colour of the plume differs between regiments but they are mostly worn by infantry regiments, especially those designated as fusilier regiments.
The large plume was originally named a heckle by the Scots, and was attached to the feather bonnet worn by the Highland regiments, drummers, pipers and bandsmen. The smaller version was adopted by the 42nd Royal Highland Regiment and to be worn as a sun helmet.
The Royal Regiment of Fusiliers wears a very distinctive red and white hackle. The regiment was awarded the hackle to recognise its defeat of the French at the Battle of St Lucia in 1778. The white hackles were removed from dead French soldiers and then in 1829 the regiment was ordered by King William IV to make their white plumes more distinguished with a red tip.