Perhaps the most distinctive feature of this bird is that it has no distinctive features at all. They are one of the UK’s most non-descript birds with brown upperparts, wings and head, beige underparts, and a black bill and eyes. This bird blends in well with its surroundings and is often heard and not seen. What they lack in appearance they make up for with their beautiful, whistling song. This song sounds similar to that of the Blackcap but has longer phrases which can take some practice to identify.
Average Length: 14 cm
Average Lifespan: 2 Years
Average Wingspan: 20-24.5 cm
During the breeding season, their diet mainly consists of invertebrates such as caterpillars and worms. Outside of the breeding season and during their migration they are frugivores meaning they eat mostly fruits and berries. Despite their name, they are unlikely to visit garden feeders.
Female garden warblers build a cup-shaped nest out of grass and roots and line it with hair, ready to lay in late May. 4 or 5 white eggs are laid and both parents incubate them for 11-13 days before hatching. They are then fed by both parents for another 10 days before fledging, after which they remain dependent on their parents for another 2 weeks. While they are usually monogamous, the male may not always be.
While the Garden Warbler is green-listed, studies indicate that it may be in long-term decline caused by several threats that may put it at risk in the future. Droughts in their over-wintering ground may lead to a reduction in the available food and reduce their energy stores for migration. In the UK the loss of suitable woodland and scrub habitat may reduce the available nesting areas for this bird and so reduce their productivity. The spread of invasive species, such as Japanese Knotweed, in Europe, has been shown to adversely affect this bird. Japanese Knotweed continues to grow and spread and as a result, populations of Garden Warblers may decrease. Finally, garden warblers are particularly susceptible to damage caused by deer as they nest low to the ground.
Be very careful if in contact with Japanese knotweed as a piece as small as 1cm can grow into a new plant.
Petition your local area to increase efforts to remove Japanese Knotweed.
Petition to protect your local woodland from deforestation and development.
The song of the Garden Warbler and the Blackcap are so similar that even they get mixed up and respect the other’s territorial boundaries!
Bauchinger, U., & Biebach, H. (2001). Differential catabolism of muscle protein in garden warblers (Sylvia borin): Flight and leg muscle act as a protein source during long-distance migration. Journal of Comparative Physiology - B Biochemical, Systemic, and Environmental Physiology, 171(4), 293–301. https://doi.org/10.1007/S003600100176/METRICS
BirdLife International (2023) Species factsheet: Sylvia borin. Downloaded from http://datazone.birdlife.org/species/factsheet/garden-warbler-sylvia-borin (Accessed: 25/08/2023).
British Trust for Ornithology (no date) Garden warbler | BTO - British Trust for Ornithology. Available at: https://www.bto.org/understanding-birds/birdfacts/garden-warbler (Accessed: 25/08/2023).
Hajzlerová, L., & Reif, J. (2014). Bird species richness and abundance in riparian vegetation invaded by exotic Reynoutria spp. Biologia (Poland), 69(2), 247–253. https://doi.org/10.2478/S11756-013-0296-X/METRICS
Hein, C. M., Zapka, M., Heyers, D., Kutzschbauch, S., Schneider, N. L., & Mouritsen, H. (2010). Night-migratory garden warblers can orient with their magnetic compass using the left, the right or both eyes. Journal of The Royal Society Interface, 7(SUPPL. 2). https://doi.org/10.1098/RSIF.2009.0376.FOCUS
Serniak, L. T., Corbin, C. E., Pitt, A. L., Steven, & Rier, T. (2017). Effects of Japanese Knotweed on avian diversity and function in riparian habitats. Journal of Ornithology, 158. https://doi.org/10.1007/s10336-016-1387-6
Svensson., L (2020) Collins Bird Guide 2nd Edn, Willian Collins ,Great Britain. P 302.