Great Reed Warbler Acrocephalus arundinaceus Scientific name definitions

19–20 cm; 22–31 g (mean 27·2 g). A large unstreaked reed-warbler with relatively heavy bill, moderately rounded tail feathers. Nominate race has diffuse, broad pale supercilium from just behind bill to no more than half way along top of ear-coverts, dusky eyestripe, brown lores and ear-coverts, narrow creamy-white eyering; crown and upperparts  , including upperwing-coverts, warm olive-brown, more rufous on rump and uppertail-coverts, tail brown; flight-feathers dark brown with narrow paler edges; below, chiefly cream, suffused with warm buff (especially on flanks), throat and belly whitish, sometimes faint grey streaking on throat  ; axillaries and underwing-coverts creamy to warm buff; iris dark brown; bill dark brown above, pinkish-flesh with dark tip below; legs pale brown or yellowish-brown to greyish. Distinguished from similar A. scirpaceus mainly by much larger size. Sexes similar, female with more restricted whitish below than male. Juvenile is brighter than adult, warm rusty brown above and buffish below. Race <em>zarudnyi</em> is paler throughout, less rufous, than nominate, greyer above, faintly olivaceous on rump, whiter below.

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Breeds chiefly in beds of reed (Phragmites), locally in stands of reedmace (Typha), growing in fresh or brackish water; rarely, in willow bushes (Salix). Prefers tall reeds with thick stems, especially next to open water. Mainly in lowlands, to 650 m in Europe, but up to 2000 m at mountain lakes in C Asia. In African non-breeding quarters occurs in reeds, reedmace, various swamp vegetation, thickets (also away from water), tall grass, garden hedges, maize (Zea mays) fields, sugar cane, savanna, forest clearings, herbage of Lantana and others; to 1800 m.

Migratory; winters sub-Saharan Africa from Sierra Leone and Liberia E to S Ethiopia, S to Namibia and South Africa (Eastern Cape). Geolocators show that the populations breeding in Europe exhibit significant migratory connectivity and parallel migration pattern, but utilise broad non-breeding regions in tropical Africa that partly overlap, particularly along the Gulf of Guinea where the majority of birds from the Spanish, Swedish and Czech populations spend their non-breeding period; the birds from Turkey winter in east Africa, while those from Bulgaria use intermediate areas (4 Koleček, J., Procházka, P., El-Arabany, N., Tarka, M., Ilieva, M., Hahn, S., Honza, M., de la Puente, J., Bermejo, A., Gürsoy, A., Bensch, S., Zehtindjiev, P., Hasselquist, D. and Hansson, B. (2016). Cross-continental migratory connectivity and spatiotemporal migratory patterns in the great reed warbler. Journal of Avian Biology. 47(6): 756–767. Close ). Migration S in Europe starts mainly in Aug, and passage within breeding range continues mostly to end Sept; initially European birds head mainly between SSW and SSE, and passage in S France and Strait of Gibraltar from Aug to early Oct, in Malta mid-Aug to early Nov, and on Cyprus mid-Aug to Oct, peaking first half Sept. In E of range (race zarudnyi), leaves W Siberia and C Kazakhstan late Aug to mid-Sept, passage across Gulf States of Arabia from mid-Aug to mid-Nov. Arrives on non-breeding grounds S of equator mostly from late Nov or early Dec; majority obviously pause in N tropics, where many moult. Return migration starts Mar, but most stay in winter quarters until early Apr; peak passage in Ethiopia mid-Apr to early May and in N Algeria early May, in Malta chiefly mid-Apr to mid-May; frequent to common on spring passage along whole N African coast. Birds marked with geolocators from the breeding populations in Spain, Sweden and Czech Republic show broadly similar parallel routes during the post-breeding and pre-breeding migrations; however, those from Turkey and Bulgaria show a pre-breeding migration over the Arabian Peninsula indicating counter-clockwise loop migration (4 Koleček, J., Procházka, P., El-Arabany, N., Tarka, M., Ilieva, M., Hahn, S., Honza, M., de la Puente, J., Bermejo, A., Gürsoy, A., Bensch, S., Zehtindjiev, P., Hasselquist, D. and Hansson, B. (2016). Cross-continental migratory connectivity and spatiotemporal migratory patterns in the great reed warbler. Journal of Avian Biology. 47(6): 756–767. Close ). Arrival in S Europe mainly from mid-Apr; first singing males in C Europe in second half Apr, peak arrival in first ten days May. In S Sweden mean arrival date to breeding sites is 19 May for males and 30 May for females; it advanced c. 6 days in 1985–2004 (5 Tarka, M., Hansson, B. and Hasselquist, D. (2015). Selection and evolutionary potential of spring arrival phenology in males and females of a migratory songbird. Journal of Evolutionary Biology. 28(5): 1024–1038. Close ). E race zarudnyi passes through Middle East Mar–May, reaching breeding grounds in N Iran in mid-Apr, W Kazakhstan in Apr and C Kazakhstan in May.

Mainly insects , also spiders (Araneae), some snails, and small vertebrates; rarely, fruit and berries outside breeding season. Recorded items are mayflies (Ephemeroptera), damselflies and dragonflies (of families Lestidae, Coenagriidae, Aeshnidae, Libellulidae), stoneflies (Plecoptera), orthopterans (of families Gryllotalpidae, Tettigoniidae, Acrididae), mantises (Mantidae), termites (Isoptera), adult and larval bugs (Hemiptera), lacewings (Neuroptera), scorpion flies (Mecoptera), adult, larval and pupal lepidopterans, caddis flies (Trichoptera), flies (Diptera), hymenopterans (including ants, wasps and bees), adult and larval beetles (Coleoptera), spiders and their egg cocoons, harvestmen (Opiliones), freshwater shrimps (Amphipoda), small snails, leech (Hirudinea), fish fry, larvae of newts (Triturus), newly metamorphosed frogs (Hyla, Rana) and small lizards. Most prey caught in short leaps as bird moves through vegetation, searching leaves and stems; some caught in the air by long jumps and flycatching techniques. In reeds feeds generally lower than A. scirpaceus, often taking prey from water surface; however, important part of food collected in trees and bushes. Forages also on ground.

Advertising song a rhythmic series of frog-like sounds  , “karra-karra-karra gurk gurk gurk chirrr-chirrr karra karra”, lasting 3–20 seconds, of same general form as song of A. scirpaceus but much louder (carrying up to c. 1 km) and notably guttural; sings for up to 20 minutes with pauses of only 1–3 seconds between sequences. Territorial song shorter and quieter, comprising harsh and grating notes (“karre-karre”) given 2–3 times, followed by high-pitched whistle. Calls a coarse clicking “thick”, “kshack” or more audible “krrack”; in anxiety hard rolling “krrrack”.

Laying from mid-May to July (peak late May and early Jun) in W & C Europe, from early May in S Europe; chiefly one brood per season, but 5–10% of pairs started second brood. Generally monogamous, but in several studied populations 12–28% of males simultaneously polygynous, attracting 2–3 females. Nest built by female, rarely with help of male, a deep, cylindrical cup of coarsely woven grass, reed and other plants stems and leaves, some plant down, spider webs and reed flowers, lined with finer plant material, sometimes also hair and feathers, average external diameter 8·9 cm, height 8·4 cm, internal diameter 5·3 cm, depth 4·7 cm, 10–200 cm (mainly 50–100 cm) above water and attached to several (2–14, average 6) reed stems, locally in reedmace or in willow over water; territory size 320–6000 m². Clutch 3–6 eggs , mostly 5 (mean in SW Poland 4·8, in S Germany 4·73), clutch size declining through season; incubation by female, 13–15 days, mostly 14 days; chicks usually fed by both parents, nestling period 11–15 days; young become independent 12–14 days after fledging. In some populations nests parasitized by Common Cuckoo (Cuculus canorus). Nesting success 44–61%, main cause of losses predation; average 2–2·7 young fledged per nest. Annual adult survival rate 47%.

Not globally threatened (Least Concern). Rather numerous in much of range; local breeder in small numbers in NW Africa (N Morocco, N Algeria, N Tunisia). European population estimated at 1,500,000–2,900,000 pairs, with stronghold in Russia. Breeding density in sample plots 2·8–28·3 breeding pairs/10 ha of reedbed. Decline recorded in W Europe; from 1970 to 1990 population decreased by more than 50% in France, Belgium, Netherlands, Denmark, Czech Republic and Slovakia, and by 20–50% in Hungary, Italy, Greece, Slovenia, Switzerland and Luxembourg; causes not clear, but climate change, habitat loss through drainage and irrigation, decreasing reed quality and lower arthropod density probably contributed to population decline. On the other hand, has expanded its range in N & E Europe during 20th century, becoming breeding species in S Finland and S Sweden and spreading N in Russia, evidently as a result of climatic amelioration and creation of suitable habitats.