Critically endangered ortolan bunting could benefit from increased crop diversity

Submitted by Michi on 24 October 2024.

Photo above: A male ortolan bunting amidst crop sprouts. By Tuomas Seimola.

Text by Sirke Piirainen

Northern European populations of ortolan bunting (Emberiza hortulana) are rapidly declining and the species is anticipated to become extinct in the area within the coming 20 years. According to our new paper published in Journal of Avian Biology, enhancing crop type diversity and increasing the amount of bare ground in well-connected farmland landscapes could help the ortolan buntings in their breeding and, thus, aid in compensating for the losses that the species faces during migration and wintering.

Ortolan buntings are migratory farmland birds which arrive to the northernmost corners of the EU in May. They spend their short summer preparing one nest and caring for their four to five offspring. In August/September they part again to Africa.

The northern European populations of ortolan buntings have been dramatically declining during the past 40 years and are now critically endangered. As long-distance migratory birds, the ortolan buntings face several challenges during their migration and while spending their non-breeding season in Sub-Saharan Africa. Because influencing these perils far away can be difficult or even impossible, the best way to help this species, from the European perspective, is to try to improve the nesting success of ortolan buntings here in our own backyard.

​                             A female ortolan bunting carrying nest material. Photo by Tuomas Seimola.

To help conservationists, we studied which factors related to agricultural landscape, crop plants, small-scale structural elements and weather might explain the rate of decline in the Finnish ortolan buntings.  

To solve this question, we needed accurate data on the bird numbers. A core team of two well-tanned ornithologists has been visiting the diminishing populations of ortolan buntings in Finland for the past 20 springs. Observing the birds means some two-hundred farms to walk through, usually at least twice as survey sites are visited multiple times during the spring, and some tens of thousands of kilometres of driving for this tireless duo.

Once arriving at the location, the survey starts with tracking down the singing male birds with the help of a playback recording. The surveyor pays special attention to neighbouring males and tries to get a grasp of how many males there are around, forming one coherent singing group. The ortolan bunting is a social species that occurs in singing groups of several males. Therefore, it is crucial that the same birds, which sometimes tend to follow the surveyor walking on his/her route, are not counted multiple times. Below, you can watch a short video describing the surveys.

 

Surveying ortolan buntings in Finland with the help of a playback recording

Another crucial information we needed to answer our study question was the type of habitat surrounding the singing group. This meant hours of fiddling with a bunch of habitat and field crop map layers for an enthusiastic PhD researcher. Finally, laying the 19-year dataset of singing group sizes on top of some habitat variables gave us a chance to find potential culprits for the ortolan bunting declines.

In more detail, we tested whether the proportion of agricultural land cover in the landscape, crop type diversity and proportion of bare ground, density of small-scale structural elements, such as rivers, ditches, roads and building surrounding the singing group, or previous summer’s precipitation and temperature, had an association with the rate of decline in ortolan bunting populations. 

                                          Typical landscape surrounding an ortolan bunting singing group in northern Europe, Finland. A crop field for finding food adjacent to taller vegetation for hiding the nest. Photo by Tuomas Seimola.

We found that ortolan bunting declines were slower in landscapes dominated by farmland compared with landscapes with less farmland. This finding may reflect the sociability of the species, as in larger farmlands there is more space for several singing males which, in turn, attract additional males and females. Larger, interconnected farmlands are usually also more intensively managed compared to smaller and more scattered fields. Smaller, isolated fields are usually surrounded by forests which the ortolan bunting avoids. Also, we found that higher crop type diversity and proportion of bare ground had positive effects on ortolan buntings. The mosaic of various crop plants and bare ground may provide a wider array of feeding, hiding and nesting places. Ortolan buntings need taller and denser vegetation to hide their nest, but also low vegetation and patches of bare soil to access and find invertebrates on the ground.

Based on our results, we suggest implementing conservation measures to enhance crop type diversity, and maybe even establishing non-crop growing stripes of ploughed bare ground. However, although these recommendations will likely enhance the breeding and further survival of the ortolan buntings, further research is still needed to determine the causes of decline.

For the full research article click here.

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