Green Roofs - GreenSpec

There is a paucity of information relating to the fauna of green roofs and much of what isavailable is anecdotal. One of the few studies is by Brenneisen (2001), who studied the birds,beetles and spiders associated with green roofs in the Basel area, Switzerland. A sample of11 roofs were found to support a total of 172 species of beetle with 10% listed in the Swissred data book. Older roofs had more species, whilst roofs with the greatest structural diversityhad the highest number of species and density of beetles. The study showed that the ability ofthe roof to retain water was a key factor in attracting beetles.Some 60 species of spider were found on the same 11 roofs. Of these 70% were from acommon group that are known to disperse well. 40% of the 60 species are registered as‘faunistically interesting’ (meaning that they are comparable to Red Data Book species -there being no Red Data Book for spiders in Switzerland). Older roofs again had a higherdiversity of spider species and roofs with the highest structural diversity had the highestnumber of species.Birds were studied on 16 roofs. There were a total of 1844 sightings, of which 1304involved a specific activity. Activities noted included (listed in order of frequency): searchingfor insects, preening, searching for seeds, searching for nesting material, roosting andsinging. The height of the roof had no apparent effect on bird use. The 25 bird species whichwere recorded using green roofs in Basel were categorised according to frequency of use(relative to the number of breeding pairs in the locality) - see table 2. It was suggested thatgreen roofs had a significant positive benefit on the first group (feral pigeon, black redstart,white wagtail and house sparrow).Table 4 Use of green roofs by various bird species in Basel, SwitzerlandGroupFeral pigeon, black redstart, white wagtail, house sparrowCollared dove, carrion crow, magpie, goldfinch, tree sparrow,Grey wagtail, wheatear, whinchatMallard, swift, house martin, swallow, spotted flycatcher, blackcap, blackbird,starling, blue tit, great tit, greenfinch, chaffinch, serinFrequency of useHighMediumLowMinimalBrenneisen also reported that wheatear, skylark, crested lark, lapwing, common tern andmallard have been recorded as breeding on green roofs in Switzerland and Germany.The use of green roofs by black redstart - a rare and protected species in Britain - is ofparticular note. A significant proportion of the UK breeding population of this species occursin urban areas and it is particularly associated with brownfield sites. The use of green roofshas therefore been suggested as a possible means of providing replacement habitat for blackredstarts when their breeding and foraging habitat is developed (Bertrand 2002, Frith et al1999, Frith & Gedge 2000, Wells 2001).House sparrow is another species which is of increasing conservation concern due to thecontinuing decline in populations. The species now features in the London and BirminghamLocal Biodiversity Action Plans. Although the causes of the decline are not fully understood,the availability of invertebrates for feeding the young has been put forward as a major factor(Summer-Smith 1999). The use of green roofs in urban areas could potentially providealternative foraging areas for house sparrows, whilst nesting sites can be designed into newbuildings or retro-fitted to existing ones.29