The common house martin (Delichon urbicum) in Eivissa

01 October 2023

The common house martin (Delichon urbicum), or white-tailed oreneta in Eivisenc, is a species of migratory passerine bird, which winters in sub-Saharan Africa and breeds in northwest Africa, practically all of Europe and even reaches some parts of eastern Asia. In appearance they are very similar to swallows (Hirundo rustica), in fact the translation into Spanish of their local name, oreneta de cúa blanca, would be precisely "golondrina de cola blanca" (white-tailed swallow). It is precisely this feature, the white colour of the tail area, which can most easily help us to differentiate between the two species. While swallows have the upper part of the obiscule area (the "arse" of the bird, to put it in a more understandable way) of a metallic black-blue colour, in aircraft it is white. Also, the size and degree of tail tail-docking is different, being more pronounced in swallows than in planes.

Apart from their physical appearance, they also share feeding habits with swallows: they are authentic biological control machines for mosquitoes and other flying insects.

The islands of Eivissa and Formentera are within their breeding area, and for this reason, during the months of June and July, at Nova Falcons we decided to participate in the voluntary census organised by the ICO (Institut Català d'Ornitolgía) on this species, and whose data are published directly by the different volunteers who participate, on the project's website: www.orenetes.cat .

They breed in colonies, i.e. several pairs build their nests in the same area. They make their nests out of mud, which they pick up with their beaks and carry back to the nest. Each year, if nothing prevents it, they return to occupy the same colonies, so it is useful to have some knowledge of the health of the nesting population locally and, relatively easily, to monitor their activity during the breeding season on an annual basis. Unlike swallows, which build their nests in the form of "balconies" (so to speak), house martins build them closed, leaving only a small entrance opening. A characteristic feature of this species, which makes it much easier to follow their populations, is that they build their nests in urban environments, i.e. they use artificial structures built by man as support for their nests, such as buildings, industrial buildings, large concrete structures...

Common house martin nest, where we can distinguish the different layers of mud used, due to the different tonality of the earth in which the different muds used were formed. As can be seen, the entrance mouth is barely imperceptible, although not all of them have to be so concealed.

The colonies present their activity peaks during the months of June and July, which is why it is during these months that the census should be carried out. During the census, we found nests, even within the same colony, with chicks at very different stages of development, which shows how heterogeneous the breeding process of the species is, and how long the breeding period is.

Without pretending to census every last nest in this first year participating in the project, and it must be said, having also done it a little as we went along because time passed and we were running out of dates. A total of 3 consolidated colonies were censused (one of them in an area of high ecological value but extremely deteriorated: Ses Feixes). We also detected a 4th colony, probably in its first year, which had a single nest in a newly built concrete infrastructure. Not all the censuses were fruitful; one municipality (Santa Eulalia) was checked and no colony was located, despite being, a priori, a favourable area. Formentera was left out for purely logistical reasons, just as, due to lack of time, other points on the island of Ibiza, including the historic area of Vila, were left unchecked. There is no doubt that it would be interesting to repeat this experience next year, adding other volunteers who so wish, in order to better cover the whole of the Pitiusan archipelago and to have a more accurate census.

The overall results of the census were as follows:

Total nests in good condition: 118

of which active nests in good condition: 107

Nests under construction: 21

As can be seen, we are not talking about a disproportionate population, and although some areas have not been checked and probably not all the nests currently on the island of Ibiza are included in this census, we do consider that the bulk of the nesting population on the island of Ibiza has been counted. Therefore, it is not unreasonable to suppose that for the Pitiusan archipelago, we have a total population of around 200 breeding pairs. Seen in this light, the need to respect and protect all the nests of the common buzzard is surely better understood. Their destruction is a criminal offence, which can lead to fines of thousands of euros, in a totally stupid way, as they do not cause any structural damage to buildings.

To put the results of this year's census into context, it is worth looking at the "Balearic map". In Mallorca, the estimated number of nests is 2,500, with about 2,000 active nests (GOB); we are talking about an estimate, because unfortunately there is a lack of technical resources to cover all the areas that it would be desirable to census on the neighbouring island. As far as Menorca is concerned, the number of nests counted is around 500, a figure that has remained more or less stable since 2010, the year in which the census has been carried out uninterruptedly (SOM).

Having said that, and without further ado, we leave you with a small "album" of the different days of the censuses, we hope you enjoy it!