Marsh Warbler

Acrocephalus palustris - Rousserolle verderolle

Systematics

Order
:
Passeriformes
Family
:
Acrocephalidés
Genus
:
Acrocephalus
Species
:
palustris

Descriptor

Bechstein, 1798

Biometrics

Size
: 13 cm
Wingspan
: 19 cm.
Weight
: 11 à 15 g

Longevity

10 years

Geographic range

Distribution

Identification

The Marsh Warbler is a close relative of the Common Grasshopper Warbler, which is very similar in appearance. The distinction between the two species is not always obvious and the best way to tell them apart is by their songs. Their habitats are also quite different. Compared to the Grasshopper Warbler, the Marsh Warbler is slightly larger and has paler, less 'warm' plumage without the red/brown tones that are present on the Grasshopper Warbler's body. Its underside is washed with pale fawn on its chest and sides, and its legs are a light pink-brown with pale claws. The bill is somewhat shorter and the forehead less prominent, resulting in a less 'pointy', less 'acrocephalic' appearance which is further emphasized when singing, with the crown feathers raised further.
Juveniles of both species look very similar and can only really be distinguished with some practice.

Subspecific information monotypic species

Foreign names

Rousserolle verderolle,
Carricero políglota,
felosa-palustre,
Sumpfrohrsänger,
énekes nádiposzáta,
Bosrietzanger,
Cannaiola verdognola,
kärrsångare,
Myrsanger,
trsteniarik obyčajný,
rákosník zpěvný,
Kærsanger,
luhtakerttunen,
Europese Rietsanger,
boscarla menjamosquits,
Seljusöngvari,
łozówka,
purva ķauķis,
močvirska trstnica,
Болотная камышевка,
ヌマヨシキリ,
湿地苇莺,
kärrsångare,
濕地葦鶯,

Voice song and call

play
pause

Marsh Warbler most often sings while perched prominently on a tall grass or small bush. Its song is very different from that of the reed warbler. It is an entirely imitative potpourri, consisting of imitations of other birds, both European and African, mostly but not only passerines. This 100% imitative singing is both the Marsh Warbler's distinguishing feature and originality. Hence, it is the most original song amongst all of our singing passerines. It easily allows the Marsh Warbler to be distinguished from the reed warbler. It can start with the repetition of one note before evolving. The most frequent call, the one uttered upon entering the territory, is a sharp tenk from a warbler, repeated if necessary.

Habitat

The Marsh Warbler occupies high herbaceous vegetation dotted with bushes, growing near watercourses and the margins of ponds and marshes, and composed of tall helophytes.

These high formations can be compared with megaphorbiae. The dominant plant is often the nettle, more commonly the meadow saxifrage at altitude. There are also phragmites, umbellifers (parsley, lovage), cirsium and thistles, epilobium, eupatorium and other large- stemmed plants. The nest is traditionally built in a tuft of herbaceous plants with stems suitable for supporting it, such as meadow saxifrage, Filipendula. Phragmity is the habitat of the Crested Tit, but is only marginally occupied, although the two species often coexist. The bushes serve as singing and territorial defence posts but also as a refuge for young birds leaving the nest.

Behaviour character trait

The Marsh Warbler leads a hidden life in the dense herbaceous vegetation it occupies, and if it wasn't for its vocal emissions, it would go unnoticed.

But once one knows it is present and it stays silent, its movements can be followed by seeing the movement of the stems. Indeed, it shares with the Grasshopper Warbler the same mode of movement in the herbaceous vegetation. It jumps or flies from one stem to another, grasping it laterally with its clawed feet, which causes the stems to swing. It hunts for the insects that are visible. The male sings while perched on a stem or bush, both to defend its territory and to attract a female. Once mated, it follows the female in her movements while singing, leaving her to do the nest building.
When disturbed, for example when someone enters its territory, one can hear its tacs of worry that it repeats as long as the potential danger persists.

Flight

Flight is easy as befitting a migratory bird, but the chances of seeing it in flight over long distances are rare as it is mainly a nocturnal migrant. The best time to observe it is during a breeding period, when it flies between its nest and the hunting grounds.

Dietfeeding habits

The Marsh Warbler is an insectivore. Its diet is broad and corresponds to the resources available at a given moment.

At the top come insects and their larvae. Floral Diptera such as hoverflies make up an important part of its breeding period diet. Caterpillars of butterflies or Tineidae are also sought. It knows how to take advantage of unexpected resources, for example during an aphid invasion or a caterpillar attack. Spiders are quite frequently captured. It happens for them to make small pellets to regurgitate items that are too big or indigestible. One can find shells of small gastropods, although it remains anecdotal.

Reproduction nesting

The Marsh Warbler is a late migrant, given the distance of their wintering grounds. They don't return from Africa until May and even early June at high altitudes.

The male arrives first and sets out to find a territory on which he tries to attract a female by singing. Once the pair is formed, the female quickly creates a nest made of dry grass, much looser than the wren's nest, which she attaches to herbaceous stems at mid-height. The bowl-shaped nest is lined with rootlets and receives 4-5 blue-green spotted eggs, which are incubated by both partners for 10-14 days. Young leave the nest at 10-11 days of age. At this point, the family splits up, each parent taking care of part of the brood until they are emancipated.
A first lost brood is replaced. Second clutches are rare but they exist in good years, when the environment allows it.
Post-nuptial depart is early and takes place as early as August. Only a minority of the population is still present in September. Indeed, the journey to their southern African wintering grounds is long and time-consuming.

Geographic range

The breeding range of the Marsh Warbler extends mainly, in longitude from Northwest France and South England to Russia, and in latitude from South Finland to the Balkans and the Caucasus with an extension to the mountainous areas of Northern Iran. In France, it can only be found north of a line from Normandy to North of the Alps.
It is an eastern type migrator whose migration routes pass through the East Mediterranean, the Middle East and East Africa. Its migration leads to the savannah areas of Southeast Africa, including the Cape region, where it winters.

Threats - protection

IUCN conservation status

Extinct

Threatened

Least
concern

Extinc
in the Wild

Near
threatened

Not
evaluated

EX EW CR EN VU NT LC NE

The Marsh Warbler inhabits uncultivated areas alongside waterways, roads, ponds, and crop fields. It is very sensitive to any damage caused by humans such as mowing, herbicides dispersal, trampling, and outright destruction. A useful form of protection that concerns other species as well is the introduction of weedy uncultivated strips with late or occasional mowing as border areas around areas of human activity, especially farming.
Climate change is obviously having a negative impact on the Warbler's habitat. Reduced rain leads to less tall herbaceous vegetation, which is less suitable for nesting. At the same time, unfavourable woody vegetation invades the soils, which lose their hydromorphy.