Discovering the nest boxes at Herdade de Espirra

Inside the nest boxes installed at Herdade de Espirra, several species of birds nest and contribute to a true “3-in-1”: more biodiversity, greater natural pest control, and greater environmental awareness.

Here and there, hanging from cork oaks (Quercus suber), stone pines (Pinus pinea) and eucalyptus trees (Eucalyptus globulus), small odd-looking structures go almost unnoticed in the landscape of Herdade de Espirra, in the heart of the Setúbal Peninsula. They can be found by more attentive human visitors roaming the 1700 hectares of this property, where pine nuts, wood, cork, and wines are produced, but there are other more important types of visitors and inhabitants: small birds, for which these nest boxes provide a great place for breeding.

Due to their characteristics (the size of the entrance, for example) and the carefully chosen locations where they are installed on the property, these nest boxes seek to attract insectivorous cavity-nesting birds, that is, specific species of birds that feed on insects and usually make their nests in the small cavities of older trees. In this way, the installation of these nest boxes ends up rebalancing the ecosystem in areas of less mature forest, making artificial cavities available to these species.

The first 30 nest boxes were installed in the winter of 2019. A year later, a new batch made it possible to increase the number of boxes available for the small birds. Today, the focus of The Navigator Company, owner of Herdade de Espirra, has shifted from installation to maintenance. The priority now is to ensure that the nest boxes are in good condition, through regular cleaning (eliminating parasites, for example), and to monitor occupation.

What has been observed is encouraging: “certainly 90% of the nest boxes are occupied”, stresses Rogério Cangarato, an ornithologist involved in this initiative at Herdade de Espirra. The specialist adds that “occupation and reproduction have both been very successful, which has led to an increase in these species on the property and at the local level”.

The birds that inhabit the nest boxes at Espirra

So it is insectivorous cavity-nesting birds that can be found in these artificial nests. But which ones in particular? The structures attract small birds that are already typical of these forest habitats, such as:

• Blue tit (Cyanistes caeruleus)
  Small in size, it attracts attention because of its exuberant colours – from the blue of the head and back (which gives it its common name) to the yellow on the abdomen. It has “Least concern” conservation status in Portugal: it is commonly seen among the branches of leafy trees and is a typical species found in cork/holm oak and mixed forests.
  
• Great tit (Parus major)
  It differs from the blue tit in that it is a little larger (it can measure between 13 and 15 centimetres in length) and because the blue tones are replaced with black. This species, whose chicks have been born in the nest boxes at Espirra as can be seen in the photos, also has “Least Concern” conservation status and is abundant in forested areas throughout the country.
• Eurasian nuthatch (Sitta europaea)
  With a long beak and a short tail, the nuthatch has an orange breast and a bluish-grey back. The colours, although striking, are not its most distinguishing feature, as the nuthatch is one of the few birds that is able to walk down tree trunks. This small bird, with “Least Concern” protection status, can mostly be found in mature forested areas.
• Wren (Troglodytes troglodytes)
  Brownish in colouring and small in size (reaching 10 centimetres in length), the wren is one of the most recognisable birds in Portugal’s forests. It also has a “Least Concern” status and prefers riverside locations and areas of dense brush.
  

A natural pest control

By feeding on the insects living in the trees, these birds are an important ally in the fight against forest pests (such as the Coraebus undatus beetle, an insect that feeds on the bark of the cork oak), demonstrating the value of biodiversity for human beings. That is also why nest boxes were developed with these insectivorous species in mind – and not any other species of forest birds.

“Basically, nest boxes increase the availability of cavities suitable for occupation by these birds – and this has other effects on the dynamics of the species and on the ecology of these areas where the nests are”, explains Rogério Cangarato. “The principle is that if we increase the availability of cavities, we can increase the population of certain species that naturally feed on these pests. Predators increase, prey decreases”, he concludes.

Increasing predatory species as a natural method of pest control provides a sustainable alternative to the application of insecticides. The initiative is part of The Navigator Company’s biodiversity conservation strategy, which thereby manages to combine the promotion of biodiversity with pest control.

The third impact of this project – in addition to biodiversity and natural pest control – is environmental education, which strengthens ties with the community. For example, the construction of nest boxes has involved the support of a vocational school in the region. But the potential goes far beyond just installation, as Rogério Cangarato points out: “nest boxes are obviously an easy way to involve young people – and others – in the importance of these projects, because people feel that they are participating directly and can help monitor the boxes, over time”.

Taking into account their potential, one of the next objectives is to make the project a model of good practices and awareness of biodiversity, by doing outreach and communication activities. At the same time, small birds will continue to find these artificial shelters for breeding in the middle of the Herdade de Espirra forest. Their sonorous and melodic songs are already common on the property and are the best “soundtrack” to illustrate the success of the initiative.