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The swallows and swifts found in the human structures and buildings the ideal conditions for them to raise their families. The bridges, the vertical walls, the eaves, the roof overhangs and the small cracks between their components, recreate exactly the places where their ancestors used to breed, the cliffs and crags! As we have built more and taller buildings, these birds have become a regular presence in our villages, towns and cities. And of all the species we share urban space with, swifts and swallows are probably the most appreciated.The birds benefit from the nesting conditions we offer them and we enjoy a free insect control service in addition to the pleasure of watching them up close! However, in recent decades the number of swallows and swifts has been decreasing and one of the causes is that our buildings no longer offer the nesting conditions that the birds need.

In summary, these birds have difficulty finding nesting sites because:

  • during the restoration of roofs, walls and bridges, the cracks where swifts breed are covered

  • new types of relief-free coating prevent swallows from sticking the mud with which they make their nests

  • the development of new construction techniques and materials allows the construction of buildings without cracks and often without conventional roofs or even eaves

  • the deliberate destruction of nests, due to the nuisance they may cause, is still common, although prohibited by law


It is therefore essential that we try to protect existing nests and colonies. But it is also important to encourage the establishment of new nesting sites, especially in places with good conditions and where nest impacts are minimal, so that the birds can settle there for many years!


Barn Swallow nests, when in the natural environment, are built in recesses in cliffs or in places where the rocks form a shield that protects the nests from the rain. Nowadays there are almost no known nests of this species in natural environments, with almost all Barn Swallows breeding in man-made structures. There are, however, some cliffs where we can still see nests of this species, like those found on the banks of the Guadiana River, at Pulo do Lobo. These birds are semi-social and sometimes form small colonies with a few dozen nests, but generally they make isolated nests. If your house has a porch, a shed or another place with good conditions for a Barn Swallow nest, you can learn here how to make a nest-cup!



How to build the nest cup

Barn Swallow nests are small clay bowls about 12 centimetres wide and 8 centimetres high, usually built under a small overhang on the highest part of a wall or under a beam. The nest bowl is open all the way across the top where the birds enter. 

Where to install the nest cup

The preferred sites of this species are easily accessible roofs, for example buildings without walls, doors or windows, such as roof sheds, agricultural support buildings, garages, porches or any other building that, being abandoned, lacks these architectural parts.



Long before man constructed buildings, Common House Martin used to breed on cliffs, and in fact still do so in some places, such as on the river cliffs of the Alto-Douro and Tagus Internacional Natural Park. These birds are semi-social and while some nest together, others nest individually. If you want to share your home with the these martins and the building is capable of housing a colony, you can place self-made nest-bowls and hope that the birds decide to keep you company!

How to build the nest cup

The nest of the Common House Martin is a clay bowl, about 12 centimetres wide and 8 centimetres high, built at the top of a vertical wall next to eaves. The nest is accessed through a small central opening near the top of the nest, about 2 centimetres high and 6 or 7 centimetres wide.

Where to install the nest cup

The nesting site is fundamental. It should be easily accessible and built under a projection that serves as a roof (eaves). Nests should be built at a minimum height of 2 metres and south-facing façades should be avoided. The preferred sites are the ridges of gable roofs, but any protected eaves can support a nest or a colony.



Sand Martins are social birds that breed in colonies. These birds excavate their nests on sandy slopes, usually along river banks, which are exposed by the effect of erosion. Colonies can range from a handful of nests to enormous clusters of over 2000 nests. Unlike other swallow species where landscape transformation and more specifically the construction of buildings has improved their nesting conditions, for Sand Martins our impact on the landscape has not brought as many advantages as it has for Barn Swallows and Common House Martins. Dams and weirs normalise the flow of rivers and the artificialisation of the banks does not allow the formation of the slopes on which they depend. On the other hand, sand or kaolin extraction sites may provide excellent places for the construction of colonies, but the continuous work ends up turning these sites into real traps for the swallows.


Sand Martin colonies are extraordinary places with the comings and goings of swallows in and out of the nest holes. It is not, however, a structure that we can build in our homes. Due to its size and the ideal locations for its implementation, this is a challenge we leave to associations or municipalities that may be interested in promoting the presence of these birds.

Ramp up  a slope supporting a colony

The nests are dug in the highest part of the slopes, especially in the lower slopes that hardly exceed 2 metres in height. The nesting cavities have an average depth of 60 centimetres but can be more than a metre deep.

​Where to install the slope?

These birds prefer to dig their nests on slopes on rivers or lakes’ banks, as this reduces the probability of being disturbed by predators. Natural erosion caused by wind and water prevents plants from establishing, which makes these nesting sites not only safe for the birds, as predators cannot climb up the slopes to the entrance of the nests, but also low-maintenance structures for the associations or municipalities that install them.



Swifts use small crevices between the rocks of cliffs and escarpments as natural nesting sites. They can also breed in caves, as is the case of the colony in Serra da Arrábida. However, the great majority of these birds nest, nowadays, in man-made structures and buildings. Once inside a space between rocks or between the tiles of the roof of an old building, swifts build a small nest made of straws, feathers and other elements they collect in flight. These materials are aggregated with the help of their own sticky saliva, until they form a small bowl a few centimetres in diameter. In the absence of such sites, boxes can be built and installed, providing a safe and permanent nesting site.

How to build the nest box

The nest boxes for swifts are larger and have a different shape than the conventional nest boxes we are used to seeing and where other birds like tits and other small passerines nest. On the other hand, as they are exposed to the weather they must be more resistant to last for many years.

Where to install the nest box

Swifts look for nesting sites that are at least 4 metres high, so the best places to install the boxes are the highest points of buildings. The ideal façades are the least exposed to the sun, so that the box does not heat up too much and the glare from the sun does not disturb the birds. As long as the height to the ground is sufficient and in front of the nests there is free space for them to fly, it is likely that the boxes will be occupied. However, it is always the birds' decision!

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