Earlier this summer, the RHS issued an appeal for a greater quantity of drought-resistant summer flowering garden plants to help ensure the adequate provision of nectar for pollinators. Impacted by the hot, dry weather, blooms are not just smaller and less vigorous, but also fading faster in the heat.
As flowers are the reproductive structures responsible for the production of seeds, one can assume that a reduction in the number of flowers may result in a decrease in seeds set. If so, what are the effects of post-pollination processes on seed and berry production, on which birds rely as a food source during the colder months?
In the wild, garden birds consume a diverse diet, primarily comprising insects, seeds, fruits, and nuts. Some species also supplement their diet with nectar and other sources. A staple food source, seeds and berries provide essential nutrients and energy. Berries also offer a source of hydration, carbohydrates, and vitamins – particularly crucial for overwintering birds and small migrant birds for refuelling.
It may be August, but it looks like autumn is here. Clearly stressed and struggling in the heat, plants and trees are in survival mode, shedding leaves and shutting down. Berries have come and gone. Blackberries, which would normally sustain birds during the autumn and winter, have come early and birds could go hungry.
We asked the Royal Horticultural Society (RHS) for comment, and Helen Bostock, the RHS Senior Wildlife Specialist explained that the severity of the impact, will depend on the stage of plant development during the drought and the duration and intensity of the water stress.
“It’s been a mixed picture for seed and berry set this year,” she said. “With a lack of spring frosts there’s actually been a bumper crop of early flowering fruit – such as plums and cherries in gardens and cherry plums, damsons and sloes in hedgerows. Raspberries came and went very quickly. And the first flush of many hedgerow bramble flowers simply frazzled in the heat and drought, failing to set into berries.”
Bostock went on to explain, that later flowering stems and those that benefitted from a little shade and some rain, looked to be promising a good crop of blackberries for wild birds and mammals. She said that there is evidence of haws and rosehips, and if, ivy has a good flower and berry set that should see many birds and other animals through the winter. “Established trees such as holly, sycamore, beech and oak have extensive roots that allow them to set seed or fruit even when conditions are dry,” she added.
With many parts of the country in drought whilst others moving into the prolonged dry weather status, the full extent of the ongoing drought’s impact, particularly in terms of yields and quality of seeds and berries remains uncertain. The prospect of long months ahead though, casts a concerning light on the well-being of birds and wildlife.
Climate migrations
Fortunately, birds can mitigate the impacts of a poor crop yields in one area by moving elsewhere. According to the British Trust for Ornithology (BTO), certain seed- and berry-feeding species, particularly Brambling and Waxwing, have been observed making eruptive movements beyond their customary range in pursuit of seed and berry crops. Notably, such movements have even led to the arrival of Scandinavian individuals to our shores. However, a prolonged and severe drought may reduce the opportunity for birds to undertake such migrations.
We also know that individual bird species may also switch between different types of food at different times of the year, or in relation to their availability. From their weekly Garden BirdWatch data and bird ringing, the BTO have observed that Siskins and Coal Tits increase their use of garden bird feeders in those years when the availability of conifer seed is reduced. The BTO adds, that there is relatively less information on the effects of berry crops on birds, in part because berry crops themselves are less well studied. Though, the familiar species that make good use of berry crops throughout the autumn and winter months, include Blackbird, Redwing, Fieldfare, Mistle Thrush, Greenfinch and Hawfinch.
Parched plants, hungry birds
Research has shown that water availability affects seed production, particularly through its influence on ovule development. Water scarcity can adversely impact various stages of ovule and seed formation, resulting in diminished seed production and compromised seed quality. Conversely, when water is abundant, flowers receive more pollen and resources, facilitating the production of more seeds.
A study published in the journal AoB Plants (Volume 13, Issue 6, December 2021) revealed a significant disparity in seed production between high-watered and drought-stressed plants. The average seed production per fruit was found to be 21% higher in the former compared to the latter. The researchers observed that drought significantly narrowed the range within which additional pollen deposition positively impacted seed production. Hence, suggesting that alterations in the pollen-to-seed relationship can serve as a reliable indicator of the impact of drought on pollinator effectiveness and, consequently, seed production.
Heat and drought stress can impact plants throughout their growth cycles, but the research suggests that the damage incurred during the reproductive and seed-filling stages can be particularly detrimental. Cell expansion commences with an increase in water uptake. In the absence of adequate water during seed formation, the process can negatively affect seed size and quality, as the cell is unable to expand. Furthermore, as water transports energy reserves within the plant to the seed, in the absence water, these nutrients are unable to be translocated, effectively reducing the seed’s size and quality.
As a crucial food source for birds, the prolonged hot and dry weather could therefore result in a scarcity of seeds, and/or a decline in their nutritional value. This situation is concerning as it may lead to a diminished overall energy intake, compromising body condition, reduced fat reserves, and weakened immune systems in birds.
Other food sources such as earthworms, which also feed other wildlife such as hedgehogs, are currently sheltering deep below, rock hard and dry soil, making them challenging to find for all wildlife. Hotter, drier summers can also reduce soil-dwelling and aerial insects, which is one of the reasons scientists have identified climate change as one of the foremost threats to birds.
How can we help?
According to the SongBird Survival charity, despite the challenges for birds, we need to resist the immediate urge to start supplementary feeding. The charity strongly advised against feeding birds in the summer.
Susan Morgan, Chief Executive, SongBird Survival, explained: “We made the difficult decision to ask people not to feed birds in the summer, as the latest science has shown that feeding birds in summer may upset the delicate natural balance of different types of birds in your local area, and may also increase the risk of disease spreading. Providing seeds via a feeder won’t necessarily be useful to birds if their diet is insects. However, fresh clean water can help songbirds all year round, who lose water more quickly than other birds.”
Instead, Morgan explained that it’s becoming increasingly important that our gardens are able to provide natural, year-round food sources, habitat and shelter, even in higher temperatures.
“Dense bushes, shady corners and dark damp spaces such as log piles, and dead hedges are all practical ways which you can provide for insects and birds, which will also help them survive when extreme weather conditions are happening, ” she said. Supplementary feeding, however should only be provided in the most difficult times of year, such as winter, when natural food sources are scarce.
The RHS adds, that to ensure we maximise the amount of seed set for birds into this autumn and winter, gardeners are urged to leave cutting back or deadheading for as long as possible.
Diversity is key
Climatic models predict that winters will become warmer and wetter, whilst summers will become warmer and drier. The frequency of extreme events such as droughts and storms are also predicted to increase. That means that safeguarding and preparing our plants, trees, and soil against the adverse climate conditions is critical. Especially for wildlife, helplessly caught in the crossfire.
For added resilience to changing weather patterns, the Royal Botanic Gardens, Kew, recommends a more diverse tree and plant palette for our gardens – encompassing both heat and drought resistance. Diverse planting will help improve soil health, store carbon, and crucially provide for pollinators, birds and other wildlife.
In the United Kingdom, gardens span approximately 1,670 square miles, representing about 20% of Wales. Consequently, resilient gardens that possess the ability to adapt and support wildlife are vital. A diverse range of plantings ensures that even if a frost or drought poses a threat to a specific insect, there will be other plants within the garden that are less affected, thereby providing compensation in terms of habitat or alternate food source.
The challenge comes in knowing which plants to use where and how to care for them in extreme weather conditions. Plants that once thrived, may be struggling now. What is clear, is that this is a challenge we must all undertake for the sake of our birds, pollinators, and wildlife.
