Personality and human infrastructures shape the nest distribution of a farmland raptor

This blog post is provided by Juliette Rabdeau and Karine Monceau and tells the #StoryBehindThePaper for the paper “Do human infrastructures shape nest distribution in the landscape depending on individual personality in a farmland bird of prey?” by J. Rabdeau, B. Arroyo, F. Mougeot, I. Badenhausser, V. Bretagnolle and K. Monceau, which was recently published in the Journal of Animal Ecology.

Animals are not randomly distributed across habitats. They select their breeding site depending on its natural conditions such as food resources but also according to human activities and infrastructures increasingly present in the landscapes. However, within the same population, individuals may respond in different ways to anthropogenic disturbances depending on their personality such as boldness. Shy individuals could be less tolerant and avoid more human activities and infrastructures than bold ones. At first sight, one might think that this kind of spatial distribution pattern could be observed only in highly anthropized habitats such as cities and suburbs vs. farmlands. However, even in a rural landscape that may appear sparsely anthropized to human eyes, human activities and infrastructures may influence the spatial distribution of individuals depending on their personality and have consequences for the population.

The Montagu’s harrier (Circus pygargus) is a raptor species that nests on the ground, formerly in natural grassland habitats, and since the last century, mainly in cereal crops. Although protected, this species is thus highly exposed to human activities such as agricultural practices but also traffic noise and activities around villages (recreative activities). In our study area, the LTSER (Long-Term Socio-Ecological Research) Zone Atelier Plaine et Val de Sèvre (ZAPVS) in western France, an intensive agricultural area of ca. 435 km², the Montagu’s harrier population has been exhaustively monitored and protected since 1995. This long-term monitoring combines both conservation programs including nest protection before harvesting and research programs. This migratory species is monitored from late April to early August in the ZAPVS. Some females are early breeders and lay their eggs in late April while others lay later in June. Since 1995 and at each nest visit, female behaviour has been measured allowing to highlight differences in boldness among them and consequences for their reproductive success in a previous long-term study.

Montagu’s harrier chicks nesting in a wheat crop in the Zone Atelier Plaine et Val de Sèvre. Chicks are around 8-15 days old. Photo credit: Karine Monceau.

Our present study in the Journal of Animal Ecology had two main objectives. First, we assessed whether the nest distribution of Montagu’s harriers in relation to some human infrastructures (buildings, roads and paths) was influenced by female boldness (bold vs. shy) and egg-laying date, using a long-term data set (1995-2013). Second, we tested the consequences of the spatial distribution pattern on reproductive success. For each infrastructure type, we considered the distance from each nest to the nearest infrastructure and the infrastructure density around each nest. Our main hypothesis was that nests of shy females are in areas with lower infrastructure density and farther from them than those of bold females. We expected the egg-laying date to shape these patterns regarding the availability of suitable breeding sites. We further expected reproductive success to be influenced by the proximity and density of infrastructures around the nest but also to vary depending on female boldness. Shy females could be more affected by nesting in a more disturbed area than bold ones.

Montagu’s harrier female flying with a vole in its claws to feed its offspring. The nest is in a barley parcel a few hundred meters from buildings in the background of the photo. Photo credit: Christophe Ingrand.

We found that nest distribution of Montagu’s harrier in the landscape was influenced by building density and female boldness. As expected, building density around the nest was lower for shy than bold females. Shy females could be less tolerant to building-related disturbance and select the most suitable breeding site with lower building density, according to their boldness. This distribution pattern may also be explained by a non-exclusive process of natal habitat preference. Offspring of shy females that are born in low building density areas could choose to settle in natal-like nesting areas. However, the building density did not affect the reproductive success of Montagu’s harrier females but path density did. Reproductive success was lower with increasing path density regardless of female density. Human activities on paths such as walkers, joggers, cyclists along with agricultural activities could create disturbance and stress for Montagu’s harriers. Moreover, human disturbance may increase after harvesting because ca. 4m² of crop around the nest is not harvested, making the nests more visible from the path. This disturbance may lead to reduced parental care and thus, starvation, stress and/or predation for offspring.

The Montagu’s harrier nests on the ground in cereal crops making chicks vulnerable to human activities such as harvesting. Since 1995 in the Zone Atelier Plaine et Val de Sèvre, all the nests are systematically searched and protected before harvesting. However, after harvesting, nests are more visible from the path (ca. 4m² of the crop are not harvested around the nest) and the human disturbance may thus increase. Photo credit: Juliette Rabdeau.

This spatial distribution pattern and the consequences on the reproductive success of Montagu’s harrier may have evolutionary implications for the population that are necessary to take into account for its conservation. In the long term, the effects of human activities and infrastructures may cause changes in the phenotypic composition of the population. However, population viability may be affected by low phenotypic diversity regarding personality traits. Our results contribute to the growing literature on animal personality and its implications for conservation. Finally, it demonstrates that even in low anthropized landscapes, our activities may have negative effects on wild animal populations. Further studies are necessary to identify the nature of the disturbance from paths and to propose appropriate conservation measures for this declining raptor species.

Ready for the first flight: the Montagu’s harrier fledgling is around 30 days and it will soon leave the nest. Photo credit: Juliette Rabdeau.

Bio: Juliette Rabdeau recently finished her PhD at La Rochelle University on animal personality and impacts of human disturbance on the Montagu’s harrier population in Zone Atelier Plaine et Val de Sèvre. She continues her works on great predators and their interactions with human activities in Finland at Deep Karelia research centre. Karine Monceau supervised Juliette’s PhD. She is working on the impacts of human activities on farmland bird populations especially human disturbances and pesticide effects.

Juliette Rabdeau
Karine Monceau

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