Booted Warbler Iduna caligata Scientific name definitions

11–12·5 cm; 7–11 g. Small Hippolais with shortish bill, rounded crown and rather short, square tail; often resembles a Phylloscopus warbler. Has rather prominent whitish supercilium , usually reaching 1–3 mm behind rear edge of eye, lores often with dark spot, and this and rather dark brown forecrown enhance prominence of supercilium (adding to Phylloscopus-like appearance); plumage greyish-brown to darker tawny-brown above , becoming plainer and more greyish in summer (with wear); tertials and greater upperwing-coverts usually with visible contrast between dark centres (shafts darkest) and pale edges; primaries brown or a little darker, brown-grey; tail has diffusely paler edges and tips of outer feathers; off-white below, rather strong buff or yellowish-grey hue on breast side and flanks; iris dark brown; bill light brownish-pink with dark culmen and diffuse dark tip, but a few have slightly longer bill with paler lower mandible; legs greyish-pink or greyish-brown, toes often slightly darker and greyer. Sexes alike. Immature is like adult but often tinged rufous above, pale at edges of tail sometimes poorly developed.

Extreme SE Finland, W & SW Russia E to Kazakhstan (except much of W & S), extreme NW China (Dzungaria), NW Mongolia and SC Siberia (upper R Yenisey and Chunskiy region); winters mainly in CE & SE India.

Steppe with low scrub (knee-high or a little higher) of spirea (Spiraea), pea species (Pisum), etc. In temperate zone utilizes overgrown pastureland, meadows with dense bushes and weeds. In S of range overlaps with I. rama in semi-desert, but then breeds in lowest scrub, whereas latter species selects taller saxauls (Haloxylon) and tamarisks (Tamarix). In non-breeding range, frequently forages in taller vegetation such as tamarisks and acacias (Acacia), as well as in lower bushes.

Long-distance migrant. Entire population spends non-breeding season in India , on average somewhat farther E & S than I. rama. Departs from breeding grounds late Jul to Sept; returns Apr­-May, in far NW part of range not until late May/early Jun.

Mainly insects and other invertebrates; caterpillars taken in summer. In various studies, diet included such invertebrates as grasshoppers (Orthoptera), bugs (Hemiptera) including aphids (Aphoidea), cicadids and ant-lions (Myrmeleonidae), also moths and butterflies (Lepidoptera), caddis flies (Trichoptera), various dipteran flies, hymenopterans (ants, wasps), beetles (Coleoptera), spiders (Araneae), and mites (Acarina); adult diet often dominated by beetles. Forages mainly in low scrub; seen to feed also, and often for long periods, on the ground, where it hops and runs quickly. Twitches tail upwards or to side, rarely downwards, while foraging and moving about.

Song a fast warbling twitter without clear pattern or repetition of notes, voice a bit guttural, phrases vary between c. 10 seconds and 25 seconds, at times longer, each phrase opens a bit tentatively, then increases in strength and pitch; similar to song of I. rama, but less loud. Call a dry, tongue-clicking “chek”, similar to one call of I. rama; also, less often, dry short trills, “tr’r’rk”.

May–Jun or early Jul; one brood per year. Nest a well-built cup of plant stems, roots and soft twigs, placed on or near ground, or up to 1m above it, in dense undergrowth. Clutch usually 4–6 eggs, replacement laid if clutch lost; incubation by female, sometimes relieved by male, period 12–14 days; chicks fed by both parents, fledged after 12–14 days.

Not globally threatened. Common in forest-steppe and on Kirghiz steppe. Density of 5·5 pairs/ha recorded in SC Siberia; linear counts of 1–2 birds/km in areas where species considered scarce. Range expanding towards W, and has bred SE Finland; this seems to indicate healthy numbers and breeding success in core of range in Kazakhstan and adjacent parts of Russia. Scattered occurrences in drier habitats more local and uneven, but still imperfectly known.