ELI at the service of Louvain-la-Neuve's house martins population

Louvain-la-Neuve is known to host many house martins in summer. At ELI-V, Renate Wesselingh and her team of MSc students monitor and follow the population. Here’s an insight into their fieldwork and an interview.

What can we see in these photos? What were you doing?

RENATE: Since 2020, we have been monitoring the house martin population in Louvain-la-Neuve closely, and since 2022 we ring the young in the nest boxes that are accessible by ladder. 

Once a week during the nesting season, we visit the different sub-colonies and take down the nest boxes containing the right-sized chicks (determined by regular observation) one by one, and the licensed ringer puts a small ring around the leg of each chick before the nest is put back in place. House martins produce one or two broods per year, which keeps us busy between mid-June and mid-September.

Why ring young house martins?

Each ring has a unique number, like an identity card. If an individual is recaptured or found dead, we can determine where it came from and how old it is. 

We also use a net to capture adult house martins in the colony to see if they are ringed. We can then check in the ringing database whether these adults were born in Louvain-la-Neuve (the vast majority) and whether they are nesting close to their natal nest, which is often the case.

Why has UCLouvain installed nests on some of these buildings? What was the aim?

The architecture of the city of Louvain-la-Neuve, with many protective overhangs, and its location next to the lake have proved ideal for the house martins, who build their own nests from thousands of little balls of mud that they collect from puddles.

There are nests or remnants of nests on many buildings in the town centre, and the colony already had a significant size in 1985. The birds and their nests are fully protected, but unfortunately it can happen that natural nests cannot be spared when a building is renovated.

Another problem is that as the city expands, mud puddles become increasingly rare as surfaces are being paved over. The house martins find a black substance in puddles on flat roofs, but nests built with this material are much less solid and break, sometimes already during the construction or renovation of an existing nest, but also during brooding or afterwards. So, they invest a lot of energy in an activity that comes to nothing, and reproductive success declines.

This led, in 2018, to the installation of over 200 nest boxes, specifically designed for house martins, at Place Cardinal Mercier and elsewhere. 

These nests have gradually been adopted by the house martins, and there are currently more couples nesting in the nest boxes than in the natural nests.

Is the house martin doing well?

Insect-eating birds such as house martins have been directly affected by the sharp decline in insect numbers over recent decades. 

The lack of building materials for nests in urban areas is also a problem for house martins.

In 2009, for example, the Louvain-la-Neuve colony produced 177 broods. By 2020, this number had dropped to just 115 broods. But in recent years, we have seen a gradual increase, with 146 broods in 2024. 

In Brussels, the population had also fell sharply, with just 33 breeding pairs in 2002. The installation of nest boxes, among other things, has enabled this number to increase to almost 500 occupied nests in 2023.

What can we do to help the house martins?

Reduce the use of insecticides in agriculture and gardens, welcome house martins that want to nest on your facade, do not destroy their nests but fix a board underneath if the feces are a nuisance.

A final point?

Please note that it is forbidden to disturb birds and their nests without a permit. 

Furthermore, if you find any martins that have fallen out of their nests, you should take them to a CREAVES centre for wildlife rehabilitation.

On the photos:

• Renate Wesselingh, professor in evolutionary ecology, and researcher at the Earth and Life Institute from UCLouvain.
• Nathan Mees, a master's student in organismal biology and ecology, and one of the two students monitoring the colony in 2025, together with Auriane Van den Bulcke (not in the photos here).
• Philippe Vandevondele, licensed bird ringer. Alexis Dall'Asta and Nicolas De Crom, from the Institute of Natural Sciences, are also taking part in the project as scientific ringers (not in the photos here).
• On the ladder: Jacob Vogel, volunteer scientific collaborator.

Article: Emmeline Van den Bosch

Photos: Bruna Gaino