Birds love berries and treat shrubs as an all-you-can-eat buffet. For example, a flock of Naumann’s thrushes in Japan have been recorded consuming 1,500 berries from a shrub in one day! The relationship between birds and berries runs deep, so much so that birds’ eyesight is fine-tuned to notice them. What do these small pearls of energy offer birds and what do berries get in return?
Why do birds eat berries?
It is not an uncommon sight to see waxwings or blackbirds gulping down berry after berry on a wintery day. Berries offer a lot of energy to birds, they are packed with sugars, fats and vitamins. However, they are low in protein meaning most birds have to turn their beaks towards other protein sources such as seeds or invertebrates.
Even birds that mainly have a diet of seeds and grains or insects such as flycatchers and finches, will not turn down an opportunity to eat berries. This is because during these colder months berries are readily available and offer a source of energy to keep birds going through the darker days. Berries are also the perfect grab-and-go snack for fueling migration where birds can stop and rest on their way to their destination.
How do birds find berries?
Birds live in a fantastically colorful world. Birds can detect which berries are ripe, which have more fats or are more sugary just by looking at them! The colour of the berries can give away some useful information. Sugary berries are darker with shades of purple, blue, and black whereas fatty berries are red and yellow.
Although birds can detect similar colors to us, they have a superpowered eyesight that we lack. Birds can see ultraviolet light thanks to a unique eye structure and an extra light detecting cell. Birds use this light to help them detect prey, find mates, and even decide which of their chicks needs more care. Kestrels look out for the UV reflecting off rodent urine they are trying to track down. Blue tits take on more of the responsibilities of feeding their chicks if their mate has less UV light reflecting off their feathers, an indication of poor condition.
Seeing UV light has its advantages when detecting which berries. The berries with more sugar or energy reflect more UV light. Whether birds use this to help them forage is debated but there are indications that they do when there is UV light present in the form of sunlight. Redwings chose to eat waxy berries that reflect UV light at times when UV light was present but when absent they weren’t picky and ate any berry.
What has the bird ever done for the berry?
When it comes to birds and berries, it may seem a one-sided relationship. After all, we usually see birds picking them and leaving a bare looking twiggy shrub behind. However, the berry shrubs also get something in return.
Berry seeds get to travel long distances away from their parent plant and find a new home. The beach strawberry that is found in California hitches a lift from two species of wading birds all the way to Hawaii and Chile when the birds migrate. Even short distances provide seeds with a higher chance of growing as they can find themselves in areas with fewer plants, less competition for resources, and less predation as their ‘parent’ plant is not sticking out like a sore thumb inviting animals to feast.
Birds offer a forestry service. They are responsible for dispersing seeds from 25% of all seed producing plants and 50% of all plants. Plants have evolved to attract birds and other creatures looking for a sweet, nutritious, and hydrating snack. When the berry is eaten, the pulp surrounding the seed, which prevents it from growing, is removed. The majority of birds pass the seeds out the other end in a less attractive state.
However, some species are much more messy at meal time and will mash the berries in their beaks and drop some of the pulp and seeds all over the ground. The culprits are usually sparrows and finches but some plants, such as mistletoe, have evolved to make their seeds extra sticky so that they hang onto the pulp forcing the birds to swallow the seeds and (hopefully) be pooped out in an ideal location to grow.
How to help berries and birds
This winter, we can help our feathered friends survive the cold, dark days or their long journeys to warmer places by providing them with berry-producing plants. Be sure to check out the native plants in your area here. You cannot go wrong with gray dogwood and winterberry holly for thrushes and cardinals and birds will also enjoy common juniper. In Europe birds enjoy hawthorn berries, bilberries, holly and rowan.