Olivia Martin, an MSc Zoology student from Anglia Ruskin University, investigated the impact of cover crops, cultivations, and other crops on winter bird populations, using 5 years worth of monitoring data at Hope farm.
In the U.K., many bird species are seeing their populations decline, partly due to the way we farm the land. To target and stop these declines, wildlife-friendly farming techniques are being investigated, such as through the work being carried out at Hope Farm.
The use of cover crops is one such technique being increasingly adopted by farmers in the U.K. Cover crops are planted in soils that would otherwise lie fallow, so that they maintain a canopy cover of green vegetation over fields. This cover helps to prevent soil erosion and can improve other soil properties, such as the soil’s chemical and biological make-up, structure, and how well the soil retains nutrients. Recent findings also suggest that cover crops can benefit farmland birds over winter, through providing food sources and shelter.
Hope Farm has been conducting cover crop/compost trials over the past 5 years, investigating the effect of cover crops and composting on soil properties, crop yields and biodiversity. These trials have included splitting three fields into quarters and delivering one of four treatments to each quarter. These treatments are: cover crop only, cover crop and compost, compost only and conventional, bare soil. As part of my Masters degree, I undertook a project with the RSPB, analysing trends in winter bird surveys to investigate bird’s use of cover crops at Hope Farm and the factors that may be affecting this use; namely crop type, tillage and field size.
I found that, on average, birds showed a preference for cover crops, with more species of birds using the cover cropped side of the trial fields than the non-cropped side of the trial fields (Figure 1). This preference may be attributed to the improvements to soil invertebrate communities, such as earthworms and beetles, which accompanies the improvements to the soil which are delivered by cover crops. Such a result reinforces the ability for cover crops to be used as a wildlife-friendly farming tool as well as a strategy for targeting soil quality.
I then looked further into the specific types of crop that may be attracting birds. I found that birds were more attracted to certain crop types than others (Figure 2), with more species of birds, as well as a higher number of birds, typically found using cover crops and oilseed rape (OSR), than bare soil (no crops) or winter cereals. This preference for certain crops is potentially due to improved foraging habitats provided through seed-bearing crops and/or the presence of more invertebrates associated with cover crops. Such a finding indicates that any vegetative cover over winter is not necessarily enough to benefit farmland birds, but rather that the type of crop, and subsequently the food sources it supplies, is important to aid wintering birds.
I further looked at insectivorous (insect-eating) and granivorous (seed-eating) birds separately, to see if either group was particularly benefiting from cover crops, however, both groups appeared to respond similarly. This is a promising result, suggesting that cover crops could be a tool to universally benefit farmland birds, particularly if cover crop mixtures are tailored to provide much needed winter food sources, with such mixtures taking into account preferred crop types.
I also found that birds preferred fields that had not been tilled over fields that had been tilled. This is unsurprising as reduced tillage has been reported to provide a multitude of benefits to wildlife, including benefiting soil communities of invertebrates, improved water retention and soil quality. However, reduced tillage also accompanies an increased risk of compaction, which could lead to reduced yields and weed issues, and cultivations are sometimes necessary to combat these compaction issues, which are encountered at Hope Farm.
Interestingly, I also discovered an interaction between cover crops and tillage occurrence. This means that bird’s preference for cover crops was dependent upon whether the field had been tilled or not. When the fields had not been tilled, birds preferred the cover cropped quarters of the trial fields, however, when the fields had been tilled, the birds showed no preference between treatments. This interaction highlights how carefully managing wildlife-friendly techniques, such as cover crops, is as important as implementing the technique itself. Furthermore, the fact that this effect was still detected, even though fields were sometimes tilled at Hope Farm, suggests that completely abstaining from tillage may not be necessary so long as the cover crops themselves are planted into non-tilled soil. This kind of management would be much more accessible and practical for farms, like Hope Farm, where tillage is sometimes required.
Figure 3. Spatial mapping of winter bird survey of Field3, Grange Farm, winter 2017/18, showing spatial distribution of birds with variation in soil/cropping treatment. Where the field was not cover cropped, the land was cultivated.
Species Codes: MP = Meadow pipit; JD = Jackdaw; S. = Skylark; RL= Red-legged partridge; C. = Carrion crow; P. = Grey partridge; RO = Rook.
The results of this study could have important implications for the new Environmental Land Management (ELM) scheme (due to come into effect from 2021) which advises the use of cover crops as a means to meet the scheme’s goals. The ELM scheme will see farmers being paid for the public goods they provide, such as thriving plants and wildlife delivered through sustainably using and managing the land. These results suggest that advising mindfully tailored cover crop mixtures used on non-tilled soils would provide the most benefits to farmland bird species.
With the continued decline of farmland birds, developing and adopting wildlife-friendly farming is crucial to mitigate these declines, while continuing to provide food for the growing British population. By doing so, we can achieve a sustainable, long lasting farming system that will allow humans and wildlife to thrive.