These fat reserves act to add an extra layer of insulation for those times when temperatures plummet and it gets really cold.
Being able to access readily available high-energy foods in the garden that help them to build these fat supplies as quickly as possible is a huge boost to the range of species that live or visit our gardens.
If we want to give your birds the opportunity to take on as many calories as possible as quickly as possible then we need to offer them super high calorie foods and one of the best options to do this is suet.
It appeals to a wide range of birds so it's a super way of attracting different birds into the garden at the same time as providing that much-needed high energy food source.
There's a huge range of choice in how you can offer suet in your garden and something to suit every situation.
Whether you choose fatballs, suet blocks and suet pellets, they all do the same job but will appeal to different birds depending on their feeding preference.
Ground feeders like Blackbirds and Robins love to pick out suet pellets scattered in leaf litter or from a bird table, while Starlings, Nuthatches, Blue Tits and Great Tits prefer hanging feeders they can pick from.
Later in winter there's no better sight than a small tribe of Long-tailed Tits crowding around a suet block or cake making the most of what's on offer!