Key points
- Winter is a challenging time of year for birds because there is less food available for them. This is particularly true for farmland species, which often rely on seed-bearing plants.
- Agri-environment scheme options are available to try to provide seeds for birds during winter, but game crops are also known to provide seeds throughout winter and into the spring.
- GWCT scientists set out to try to understand if the food provided by game crops in winter can increase breeding bird numbers in the following spring. They did this by recording birds in hedges at different distances from game crop plots within farmland and grassland, during the spring.
- Surveys found that hedges closer to game crop plots had more breeding birds than hedges further away, with hedges within 100m of game crops having twice as many birds than hedges over 1km away, on average.
- These findings help us understand the wider benefits of gamebird management for biodiversity. In more intensive farming landscapes, winter game crops may be an effective way of holding breeding songbirds in an area through late winter and into the spring.
Background
Populations of birds in managed grasslands have declined across the UK since the 1970s. Some species populations have fallen by over 50% in this time, and farmland specialists have been the most impacted. These declines are thought to be the result of agricultural intensification and simplification of farmland – a shift from more natural, complex farming landscapes to more ‘industrial’ areas dominated by single crops. Declines in farmland and hedgerow breeding bird populations are also linked to a lack of food resources and shelter during the winter.
Lack of winter food resources, such as seed-bearing crops, can be a serious problem for birds. Species such as the reed bunting, cirl bunting, twite and house sparrow have lower rates of winter survival when food is scarcer.
Wild bird crops that provide food throughout winter, for example through agri-environment scheme options, both attract and support birds during the winter.
Plots of game crops on shooting estates have been shown to support relatively high densities of farmland and woodland-edge birds during the winter. These game crops are grown to benefit gamebirds such as pheasants and red-legged partridges for shooting, and commonly include plants such as maize, kale and cereals. The shooting season ends on 1 February, and so game crops are designed to provide food throughout the winter until then, but often provide food into early spring. Larger shoots tend to have high numbers of larger game crop plots, with these plots shown to be of great benefit to wintering songbirds.
In some parts of the UK game crops can be the main, or only, source of seeds available to farmland birds during winter. The link between these game crop plots, higher numbers of wintering songbirds, and better winter survival of songbirds, has been well studied. However, it is not clear whether winter game crop plots support spring breeding activity in these birds, after most game plots have been cut and ploughed.
What they did
The researchers set out to investigate if game crop plots benefitted hedgerow-dwelling birds. They completed a pilot study in 2017 that provided promising results, but was complicated by differing management across the study sites. After reviewing their initial findings and methods, the team began further research through this study in 2021.
The study took place across three shoots on the edges of Exmoor National Park in South West England. In total around 80 game crop plots were included in the study, which were each 1.8ha on average. Detailed maps of each estate were produced, highlighting the locations of each game crop plot and nearby hedgerows.
Zones were mapped from the edges of each game crop plot, from the 50m closest to the plots to distances beyond 1.1km from the plots. These zones, combined with site visits to check the hedgerows were able to be safely surveyed, were used to identify and select the hedgerows used in the study. A total of 53 game crop plots were suitable for the study, with 240 hedges surveyed. The height, width and density of the hedges was measured.
All 240 hedges were surveyed for resident bird species – once during early spring, and once during late spring to early summer, after migrant species had arrived. During these surveys birds perching on, calling from, and flying in and out of the hedges were recorded.
Statistical tests were then completed to investigate how the distance from game crop plots may influence the number of birds recorded in a hedgerow, and what impact hedge characteristics may have.
What they found
The scientists found that in the following spring, hedges closer to game crop plots had more resident birds than hedges that were further away. At the peak of breeding bird season in April/May, hedges within 100m of a game crop plot had an average of 1.5 more resident songbirds than hedgerows more than 500-800m away.
Hedgerows within 100m of game crops had twice as many birds, on average, than hedges over 1.1.km from a game crop plot. Hedgerows up to 300m from game crop plots also had significantly more birds present than hedges 1.1km or more away.
More resident bird species were recorded in taller hedges, but the width of the hedges did not affect the number of birds present. Hedge density appeared to have a mild impact on the number of species present, but this depended on the height of the hedges.
What does this mean?
Despite hedge height and density appearing to have some influence on bird numbers, the number of birds in hedges near or far away from game crop plots was not related to hedge size. Hedges near to game crop plots had more breeding birds than hedges further away from game crop plots – regardless of their size.
The findings of this study suggest that more breeding birds were recorded in hedges nearer game crop plots because the plots were present during the previous winter, and so benefitted the birds in the build up to breeding season.
The low availability of seeds and invertebrates in intensive agricultural landscapes, usually dominated by grassland for livestock grazing, can be very challenging for songbirds and likely results in fewer birds surviving the winter. Confirmation from this study that game crop plots benefit breeding songbirds in nearby hedgerows is very positive, and demonstrates that game crops can have wider biodiversity benefits. While designed to support gamebirds, these game crop plots provide food resources through the winter and spring for seed-eating birds such as linnets and chaffinches, and other birds such as robins and blackbirds that have a more varied diet but rely on seeds throughout winter.
There are existing agri-environment scheme options that can support songbirds in winter, however there is mixed evidence of their effectiveness. For example, the crops included in some options may need to be supplemented with extra food towards the end of winter. This study shows that providing seeds via game crop plots can help songbirds enough during winter to boost spring breeding numbers. In intensive farming landscapes, land managers should consider if game crops can complement or replace agri-environment scheme options.
Read the original paper
Sage, R., Woodburn, M., McCready, S., and Coomes, J. (2024). Winter game crop plots for gamebirds retain hedgerow breeding songbirds in an improved grassland landscape. Wildlife Biology, e01156.