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Slaty-backed Gull Larus schistisagus   - Adults
Slaty-backed Gull
Photographer : © Amar-Singh HSS
Location :Nemuro Peninsula, East Hokkaidō, Japan
Date : 5 June 2019
English synonyms:Slatey-backed Gull
Bird Family :Larini - Gulls
Bird Group :CICONIIFORMES
Red Data Status :Least Concern
Remarks :We saw many gulls during our time in Hokkaido and of interest were the Slaty-backed Gulls using the roofs of man-made structures to make their nests. Hasebe (2013) who studied the characteristics of roofs utilized by Slaty-backed Gulls in Hokkaido showed that the gulls “…. preferred flat roofs, or sloped roofs with snow guards attached, that ensure the stability of nest. The preferred nest position was roof edges…..”. Brazil (2018) says that these gulls nest on grassy islands and cliffs but in Hokkaido also on roofs. We saw quite number nesting in summer along the coast and port environments, and some did choose to use roofs. All the ones we saw were nesting on metal roofs with no railing guards but, since the slope was not steep, they had built nests near the top of the roof. Some were already incubating while others were collecting nesting material – dried grass. There was some competition for locations to obtain nesting material. All the birds shown are adults in summer/breeding plumage. There is some data suggesting that the average number of nestlings per unit is significantly higher on roofs than in natural areas (Hasebe 2013). Nests are large structures; easily more than 1 meter across and built of sizable volumes of grass and seaweed. These gulls nest communally and the density is about 2 nests/m² (more scattered on slopes). Hence I am concerned with the impact of so many nests together with adult pairs and juveniles not yet fledged on the integrity of roofs (also when wet weather makes nests heavier). In addition the tolerance of the roof owners to these residents as nesting numbers grows is of concern. Here they were using commercial, port buildings and appear to be tolerated. It would be important for new structures built along the coast to factor in gull roof nesting when being developed.
References
1. Mark Brazil. Birds of Japan. Helm Field Guides 2018.
2. Makoto Hasebe. Characteristics of roofs utilized by Slaty-backed Gulls Larus schistisagus for nesting in coastal Northwest Hokkaido, Japan. 2013 Bird Research Volume 9 Pages S13-S18 (available here in Japanese & read via Google translate: https://www.jstage.jst.go.jp/article/birdresearch/9/0/9_S13/_article).
3. Nicole on Oiseaux Birds (http://www.oiseaux-birds.com/card-slaty-backed-gull.html).
4. Burger, J., Gochfeld, M., Garcia, E.F.J. & Kirwan, G.M. (2019). Slaty-backed Gull (Larus schistisagus). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona.
-Amar
Taxonomic Notes :