The pop of red from holly berries against the glossy dark green of prickly leaves screams Christmas to us. For thrushes, blackbirds and finches it is a winter larder, providing food at a time of year when they desperately need calories from sugars and fats in fruits to survive long cold winter nights.
While these birds mostly eat protein-rich invertebrates like worms and insects in the spring and summer breeding season, they rely on fruits in the winter survival season.
Many native trees and shrubs provide natural bird food over several months in the winter. In return for this critical nutrition from the plants, animals process and move the seeds to suitable places to germinate and grow. While both animals and plants benefit from this ecological interaction it is not without its drama and conflicts.
Plants have specific needs from their animal partners. Seeds must be undamaged and deposited in a suitable site for germination and growth. It can be advantageous for the plant if their offspring are transported to a new location, far from the parents where they are not in competition with their siblings and to escape from diseases and pests that plague their parents.
Mrs Brown’s Boys Christmas Special review: Unkillable comedy’s wit is as sharp as a mouthful of Brussels sprouts
Megan Nolan: A conversation with a man in his late 30s made clear the realities of this new era in my dating life
The Big Irish Times Quiz of 2024
Róisín Ingle: My profound, challenging, surprisingly joyful, life-changing year
Plants employ defences and chemical warfare to manipulate their animal dispersers. If too many fruits are eaten by the same animal the seeds will all be deposited in one spot, a highly competitive environment and one vulnerable to pests.
It is in the plant’s interest therefore to spread out the consumption among many dispersers and over a long time-frame. Holly does this by providing only a small amount of fruit relative to the size of its seeds and by packing them with toxic compounds. The fruits are consequently not very attractive to larger animals which would consume more of them in one visit.
Yew and spindle trees go a step further and make their seeds highly toxic. All parts of the yew tree are poisonous, with one exception, the red fleshy cup surrounding the seed which is eaten by birds and squirrels. The smooth white seed of the spindle is toxic and distasteful to insects and mammals, but the bright orange seed-covering is more nutritious than any other native fruit.
The attractive fruit gets eaten but these toxic seeds are either not swallowed by the animal at all and just dropped on the ground, or are swallowed and vomited up, or pass through the animal and pooped out rapidly. The laxative properties of seeds and fruits are well known and have evolved to ensure that the seeds are not damaged through prolonged exposure to acids and microbes in the gut.
Many animal-eaten seeds are dependent on the interaction. Germination of ivy is much better once the pulp has been removed from the seeds by birds. Being deposited in a nicely manured pile of faeces is a great start in life for many seedlings. They have access to important nutrients like nitrogen from the animal’s waste.
Larger animals like foxes are responsible for a surprising amount of plant dispersal. Foxes gorge on blackberries and rosehips in autumn, defecating seeds over long distances as they forage around the landscape.
The thickets of prickles of brambles and wild rose are barriers to prevent animals like foxes from eating too many of the fruits and ensuring that other smaller dispersers, which carry seeds over shorter distances, have access to the fruits as well.
Hedgerows are packed full of bird food, if we let them grow enough to produce fruits. Our gardens can be made much more bird friendly by planting native fruiting trees and shrubs like holly, spindle, yew, viburnum, wild rose, hawthorn and blackthorn. Not only do the fruits provide much needed winter colour and interest for people, they are a lifeline for birds and other animals. Having a variety of different food sources in their environment ensures that if conditions are hard, something will usually be available.
The change in our weather patterns due to climate change affects when and how much food is available to wild animals. Give them a helping hand by providing nutritious and long-lasting food sources in gardens and on farms by protecting and enhancing hedgerows and by planting native shrubs and trees. Late winter is a great time for planting new trees.
Prof Yvonne Buckley is co-director of the Co-Centre for Climate + Biodiversity + Water at Trinity College Dublin
- Sign up for push alerts and have the best news, analysis and comment delivered directly to your phone
- Join The Irish Times on WhatsApp and stay up to date
- Listen to our Inside Politics podcast for the best political chat and analysis