Birds are a welcome sight by many farmers and land managers. Their morning choruses signal the arrival of spring, and a charm of finches, a murmuration of starlings or a volery of long tailed tits bouncing in the air is sure to brighten any countryside walk in winter. With the increasing awareness of the poor state of UK birds, the provision of breeding boxes is a common conservation practice used to support bird populations. This blog will review the effects that this practice can have for birds and soft-fruit production.
Bird boxes come in many shapes and sizes, and these differ depending on the bird species they are meant to attract. The species that occupies the box will affect how the local bird community is affected and how this translates to ecosystem functions within the farm that can affect crop yield and quality.
With increasing numbers of nest boxes emerging across our farmlands, this conservation practice has also been receiving growing scientific attention. Scientists have primarily explored these two questions:
1. Are bird boxes good for bird diversity?
2. How can provision of nest boxes affect crop production?
In this post, I’m going to summarise the answers to these questions so without any further ado, let’s dive into some science.
Are bird boxes good for bird diversity?
If I ask someone why they provide nest boxes for birds, the most common answer I’ll get is to encourage birds, of course! But does this practice actually work?
Nest boxes can be built to encourage passerines (or “garden” or “small” birds), or larger birds including owls and raptors. The effectiveness of providing boxes to increase on-farm bird populations has been tested with overall positive results.
Let’s start over in Californian vineyards where one research group led by Julie Jedlicka built 46-48 nest boxes for a small insectivorous (insect-eating) species, the Western bluebird. Here, the nest boxes led to changes in the vineyard bird community. The abundance of insectivorous birds in vineyards with nest boxes was 2.6 times higher, which was driven by the increased presence of fledgling bluebirds. However, the overall bird diversity remained unaffected.
Provision of nest boxes in vineyards may not alter the bird species composition at the landscape scale. A team of researchers also led by Jedlicka surveyed bird communities in vineyards with and without nest boxes, and within woodlands surrounding them. The species richness of birds within vineyards was primarily driven by woodland presence and not the boxes. This suggests that retaining natural vegetation cover around vineyards is key for supporting diverse communities of birds, but provision of nest boxes can effectively support bird species already using vineyards.
Though other studies have not monitored the changes in bird diversity that might have been brought about by nest box installation, it’s interesting to note that bird species common to UK vineyards such as great and blue tits, house sparrows, kestrels and barn owls became common residents.
How can provision of nest boxes affect crop production?
The simple answer is – (mostly) positively! Whatever bird species you’re attracting with nest boxes, they are likely to affect ecosystem functions within your vineyard. Aside from breeding in the nest boxes, the birds are likely to feed within the crop and consume whatever’s around. Insectivorous birds may turn to insect pests, whilst birds of prey to the fruit-eating bird species.
With the growing interest in measuring ecosystem services, these dynamics have been reasonably-well studied. Vineyards and fruit orchards with nest boxes were found to experience less herbivory and higher consumption rates of insect pests by birds. In some systems, this effect was impressively strong – for example, caterpillar damage in apple orchards with nest boxes was reduced by 50%!
Many insectivorous species are generalist predators and may be consuming natural enemies of pests. This was found to be the case in the Californian vineyards where breeding birds consumed pests and their natural enemies. This risked an increase in pest abundance resulting from reduced pest control by the natural enemies, but luckily, the overall abundance of pests in vineyards with nest boxes was lower. This does, however, highlight a risk that is worth bearing in mind!
When your problem is with fruit-eating birds, nest boxes might also be the answer. In cherry orchards and vineyards in America, the provision of nest boxes for kestrels led to a reduction in the abundance of fruit-eating species. In fact, this effect was so strong in one orchard that the scientists estimated that for every nest box built, $84-$357 of cherries were saved!
I’m making nest boxes seem rather amazing, right? Before we all get too excited, it’s important to highlight some caveats. The provision of ecosystem services is variable between farms. For example, the provision of nest boxes in organic apple orchards did not result in a reduction in caterpillar damage. Even in cases when birds successfully control pests, this service may be localised to areas immediately by nest boxes as breeding birds don’t like to stray too far. Another issue is with attracting birds to breed in the boxes in the first place, which seems to improve with time from box installation, but nest occupancy can remain low and variable. For example, the average nest occupancy by raptors was found to be 30% across years, but this was highly variable between years and sites, as some sites in some years failed to attract breeding raptors.
Take home message
Nest boxes are a great conservation practice that can support local bird communities, but much remains much to be discovered. There’s no doubt that with careful management, nest boxes could be used to benefit bird diversity and crop production but it’s important to remember that vineyards are complex systems and the effectiveness of nest boxes at attracting desired bird species is likely to be impacted by vineyard management and the surrounding landscape.
What are your experiences with nest boxes? I’d love to hear your stories, and as always, if you have any questions or would like to discuss the nest boxes at your vineyard, don’t hesitate to get in touch!
About the author
My name’s Natalia Zielonka, and I’m a PhD candidate at the University of East Anglia. I’m supported by the UKRI BBSRC Norwich Research Park Biosciences Doctoral Training Partnership, and my great supervisors are Dr Lynn Dicks (based at the University of Cambridge) and Dr Simon Butler (UEA). If you have any questions then please don’t hesitate to contact me on [email protected] and via Twitter: @Nat_B_Zielonka.