Europa - Birds

Swallow / Sand Martin

The sand martin is not a well-known bird species in Croatia. Its scientific name, Riparia riparia, means “of the river bank” and it is suggestive of its nesting habitat. The sand martin is a colonial bird species, so many birds nest at the same site. They choose steep riverbanks covered in pebbles or sand and dig horizontal burrows in them at a height where they cannot be reached by the river. These canals can be as much as one metre long and they slant slightly upwards in order to prevent potential flooding. A small chamber at the end of the canal contains a delicate nest made of feathers and twigs. In May and June, the female uses this nest to lay four, five or six eggs. A sand martin pair can produce two broods a year and it produces the first within the first year of its life.

Both the male and the female sit on the eggs, switching places over the course of about 16 days. When the chicks hatch, they are fed by both parents.

In appearance, the sand martin can be reminiscent of a more well-known bird species: the barn swallow (Hirundo rustica) with which we are more familiar because it is more widely present in our landscape, especially in the Croatian countryside. The sand martin has a similar body shape, but it is smaller. It is between 11 and 12 cm long, its wings and back are brown, while its abdomen is white. A brown stripe is visible on its breast. Its legs are short. Its wings are sharply pointed and its tail is slightly forked. While sand martins are on the wing, their twittering is continuous and they remain “chatty” even as they briefly rest in a roost. The two genders are very similar, which means that it is difficult to tell males and females apart at first sight. The sand martin feeds in flight, catching insects.

It is a migratory species and winters in Africa, in Sub-Saharan areas and along the east coast, all the way to its southernmost point. It migrates during the daytime. In Croatia, a mass ringing of sand martins was performed in colonies nesting on the River Neretva.

The sand martin is present all over Europe and, in Croatia, it can be found near open waterfront areas, as well as in wetlands near the Mura, Drava, Sava, Danube and Neretva Rivers.

This bird species is endangered, which means that the number of nesting pairs is decreasing. This is the case across Europe, including Croatia. It has been estimated that nowadays between 6,000 and 8,000 pairs nest in Croatia. The main cause of the decrease in their numbers is the loss of wetland habitats. In 2016, the sand martin was therefore pronounced the bird of the year in Croatia. This was meant to draw the public’s attention to the fact that the species is going extinct in Croatia and encourage responsible individuals in our country to take action in order to prevent its disappearance from the wetlands with which it forms an indivisible ecological whole.

Yellow-legged gull

When we mention gulls, the image of Jonathan Livingston Seagull crops up in our minds, reminding us of the symbolism of achieving knowledge in free flight, which was outlined by R. Bach (1970). Croatia is a maritime country and one of the most beautiful things connecting its sea to the sky is the yellow-legged gull, Larus michahellis.

There are more than 50 gull species around the world and, in Croatia, the yellow-legged gull nests on distant and uninhabited isles and islets in the Adriatic. It used to be considered a subspecies of L. cachinnans michahellis, but nowadays it is categorized as a separate species.

The yellow-legged gull is characterized by its yellow legs and grey back and wings with darker tips on the primary flight feathers. It has webbed feet. Its neck and abdomen are white, while its bill is yellow with a bright red spot on the lower jaw. It is between 55 and 67 cm long and its wingspan varies between 130 and 150 cm. The two genders look similar.

The yellow-legged gull lays eggs on the ground with sparse vegetation but nesting on rooftops has also been recorded (Rovinj, Istria). It nests in colonies. It is ready to nest at between three and five years of age. It produces only one brood a year. In April, May or June, the female lays 2 or 3 eggs. Both the male and the female incubate the eggs for 28 to 30 days and both feed the young. The chicks stay in the nest for another 35 or 40 days. The yellow-legged gull can live for 10 years or longer.

Its diet consists of fish, crabs and shellfish, but it also relies on other food of animal or plant origin. In order to feed, it enters inhabited areas and travels deeper into the Croatian mainland to visit landfill sites where it has also been known to gather in larger numbers. Its diet can also include carrion.

The yellow-legged gull population in Croatia has been estimated to include between 40,000 and 60,000 nesting pairs. This species is not endangered, but stable; however it is protected by law (The Rules on the Protection of Certain Bird Species (Aves)), so locals are not allowed to take its eggs. If its nest is robbed, the yellow-legged gull makes up for the loss by producing another brood in the same season.

The yellow-legged gull is a resident bird and it spends the entire year near its nesting site. However, young gulls can take part in dispersive migrations outside the Adriatic area, moving inland to visit fresh waters, and some have even been known to migrate to the coasts of northern Europe, from where they returned to the Adriatic. These migrations by the local yellow-legged gull populations have been proven by ringing and bio-marker analysis, which was performed in Croatia for the first time (1988).

Jasmina Mužinić, PhD, retired Senior Research Fellow