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18
Green Roofs – Urban Habitats for
Ground-Nesting Birds and Plants
Nathalie Baumann and Friederike Kasten
ZHAW Zurich University of Applied Sciences, Institute of Natural
Resource Sciences, W¨
adenswil, Switzerland
Summary
In this study, vegetation establishment and breeding success (from egg laying
tofledgling)onflatroofsinperi-urbanandindustrialzonesinSwitzerland
were examined. Seven green roofs in peri-urban and urban areas in different
Swiss cantons (Aargau, Berne, Zoug and Lucerne) where Vanellus vanellus
(Northern Lapwing) and Charadrius dubius (Little Ringed Plover) may breed
successfully were investigated. In addition, a ground site in an agricultural area
was used as a control or reference site. The project had two objectives: first,
to improve the vegetation of the roofs using different techniques – seed, hay
mulch (fresh and dry) and turf – and, second, to assess the development of the
vegetation in relation to improving the breeding success of, and habitat use
by, V. vanellus. Because the research project funding ended in July 2009, the
data presented in this chapter are from only one of the roof sites (Rotkreuz),
which provides a good overview. The data were obtained over three breeding
seasons. The initial results suggest that the improvement of green roof habitats
using fresh hay mulch produced a vegetation of 90–100% in two seasons,
resulting in a remarkable increase in plant biomass. Results also show that
V. vanellus has begun to breed consistently, although as yet unsuccessfully on
Urban Biodiversity and Design, 1st edition.
Edited by N. M¨
uller, P. Werner and J. G. Kelcey. ©2010 Blackwell Publishing,
ISBN 978-1-4443-3266-7 (hb) and 978-1-4443-3267-4 (pb)
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Urban Habitats for Ground-Nesting Birds and Plants 349
green roofs. The results show that as a consequence of the improvement of
the vegetation, the chicks survived 5–10 days longer in the second year than
in the first year. The study has provided important information about the
habitat selection and behaviour of the adult and young birds, which is of value
in future urban research and green roof design.
urban biodiversity, extensive green roofs, ground-nesting birds, Vanellus vanellus,
breeding success, vegetation methods, Switzerland, ecological compensation areas
Introduction
Clergeau et al. (2006) state that the human population is growing and that the
extent of urban areas is expanding faster than the number of inhabitants. As a
consequence, large areas of agricultural and other land (including open areas
with damp soil) are being used for residential and industrial development.
This results in a threat to the existence of many plant and animal species in
Switzerland from habitat loss and fragmentation. However, extensive green
roofs can provide suitable compensation as a habitat for some animal and
plant species that are able to colonize roofs, adapt to the difficult conditions
and develop strategies for survival in ‘extreme’ local environments Brenneisen
(2003).
In 2005–2006, a literature search was carried out to obtain information
about the use of green roofs as a bird-breeding habitat. None of the literature
reported information about successful breeding; it also appeared that the
observation periods were too short, unsystematic and otherwise inadequate to
acquire reliable data about the behaviour of ground-nesting birds on roofs.
The research project reported in this chapter was devised to provide the
much-needed information. The main objectives of the 3-year (2006–2009)
project ‘Ecological compensation on roofs: vegetation and ground-nesting
birds’, funded by the Federal Office for the Environment (FOEN) were to
1. determine the breeding behaviour and success of ground-nesting birds
(adults and chicks);
2. find key factors to optimize the roof habitat for their needs (developing
guidelines for green roof design);
3. test different methods for the establishment and management of suitable
vegetation (local sources, sustainable and reasonably priced);
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350 Nathalie Baumann and Friederike Kasten
4. develop new technologies and systems for ecological compensation mea-
•Q1
sures;
5. establish and improve the roof vegetation to enable Vanellus vanellus chicks
to grow and fledge successfully.
This chapter describes the research undertaken between 2006 and 2008
to analyse the vegetation and bird breeding at one of seven sites – Rotkreuz
(Canton Zoug, 3M Company and Sidler Transport AG). We predicted that
with good weather conditions and three growing seasons, the increase in
biomass of the improved habitats should result in sufficient insect production
to support chicks of the ground-nesting bird V. vanellus. In addition, we
examined whether there were any possibilities for assessing the suitability of
the surrounding area as breeding habitat for ground-nesting species and, if
so, whether we could encourage the birds to use more ‘natural’ habitats to
breed. We focused our analysis of breeding on observations of the behaviour
of breeding pairs and their chicks. The vegetation cover was assessed using the
phytosociological method of Braun-Blanquet (Dierschke, 1994).
Ground-nesting birds in Switzerland
In the last decade, ground-nesting birds appear to have adapted to breeding
on extensive flat roofs instead of agricultural areas. This secondary habitat
was chosen by V. vanellus following the loss of their former habitats such as
open areas, grasslands, fields, moors, bogs and heath, which have decreased
drastically throughout Switzerland during the last 100 years as a result of
improvements in land drainage (Schweizerische Vogelwarte Sempach, 2008).
In addition to V. vanellus, the other ground-nesting birds that were breeding
on flat roofs were Charadrius dubius (Little Ringed Plover), Alauda arvensis
(Eurasian Skylark) and Galerida cristata (Crested Lark). V. vanellus is native
to temperate Europe and Asia; 50% of the European population breed in
Britain, The Netherlands and North Germany. The species normally breeds
on cultivated land and in areas of low-growing or maintained vegetation. The
first clutch (three to four eggs) is laid in a scrape in the ground; the chicks’ hatch
after about 26 days of incubation. If the first brood is unsuccessful, the adult
birds are able to lay up to seven replacement clutches on a new site or on the
same site but several metres from the first nest. The chicks leave the nest early
and, after 42 days, are able to fly. From the first day of their leaving the nest, they
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Urban Habitats for Ground-Nesting Birds and Plants 351
have to forage and drink by themselves, which is a complex problem on roofs.
The standard green roof (for example, a lava –pumice substrate colonized by
Sedum spp.) does not supply enough food for the chicks to survive and grow.
This is because vegetation is sparse and low growing; consequently, it does
not attract and support sufficient insects that can establish and develop their
life cycles (eggs, larvae, nymphs). A rich diversity and quantity of insectes
is necessary to support the chicks because they require to survive and grow
many insectes (larvae, nymphes etc). The development of the insectes biomass
depends on a large species and structural diversity of plants. The plant biomass
development is determined by the thickness and type of substrate. There is a
growing tendency in Switzerland for ground-nesting birds such as V. vanellus
(an endangered (EN) in the Red List of Swiss breeding birds; of least concern
in the International Union for Conservation of Nature (IUCN) Red List)
to regularly use flat roofs for breeding; therefore, it is of great importance
to optimize the design and construction of roofs to support and fulfil the
ecological needs of this and other species.
Methods
Sites and ground-nesting birds
We examined the roofs at seven sites where there had been single observations
of V. vanellus and C. dubius (see Figure 18.1). The sites were located in four
different Swiss Cantons (Aargau, Berne, Lucerne and Zoug). The surroundings
of the sites varied from urban to rural. From 2005 to 2008, the use of the roof
habitat for breeding by these two species was recorded from the end of March
until mid-July. From the time of arrival of the breeding pair, observations
were made weekly for 3 hours at the same time of the day. During the
breeding period, observations were made three times per week and when
the chicks hatched, the frequency was increased again (4 hours per day/site);
observation continued until they died, disappeared or fledged. Observations
of the replacement clutches were done using the same method. Observation
was made with binoculars (Nikon 10 ×42 mm) and telescopes (Nikon Field
scope EP, 13x - 56x). Foraging behaviour, movement patterns, habitat use and
other behavioural activities were recorded, together with information about
the habitat, vegetation and roof. So as not to disturb the birds significantly, the
observations were made primarily from adjacent buildings with good vantage
points (Baumann, 2006).
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352 Nathalie Baumann and Friederike Kasten
Figure 18.1 AmaleVanellus vanellus on the Rotkreuz roof, around March 2007
when the breeding season starts. The sparse vegetation of this roof comprises
moss, lichens, Sedum polster and very few herbs growing on bare gravel (2007,
N. Baumann).
In 2008, as a result of the problems caused by the 2007 drought and to
prevent a repetition of them, a rainwater irrigation system was installed and a
9m
2pond was constructed on each of the seven roofs to irrigate the vegetation,
provide water for the adult birds and the chicks and to create conditions that
would attract a large population of insects, for example, Chironomids and
other dipterans.
Vegetation
As suggested by K¨
ohler (2006), it is possible to create a relatively diverse
flora on extensive green roofs in inner cities as well as in rural areas. He
also suggests that plant diversity can be even higher if varied micro-climates
(especially sunny and shady areas) are created, initial plantings are enhanced
and a minimal amount of irrigation and maintenance is provided.
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Urban Habitats for Ground-Nesting Birds and Plants 353
From the start of the study, the roofs supported various vegetation types,
whichrangedfrommossesandlichensongraveltoSedum spp, Dianthus
carthusianorum, grass species and moss on lava–pumice substrate. The land-
scape and vegetation design of four of the seven roofs could be improved by
increasing the vertical and horizontal structure of the vegetation and, there-
fore, the invertebrate biomass. It was, therefore, decided to test three methods
of doing so; first, by applying a hay mulch (dried or fresh and applied in
layers); second, sowing seed (a mixture of indigenous meadow plants specially
formulated for green roofs); and third, the laying of turves. All the three
techniques were applied to 4–6 cm of ‘ricoter’, which is a Swiss roof topsoil
substrate made from recycled material.
Rotkreuz roof (building of the companies: 3M and Sidler
Transport AG)
For the last decade, V. vanellus has been seen on the 40-year-old flat roof
(approximately 12,000 m2) of a building occupied by 3M and Sidler Transport
AG in the industrial zone of Rotkreuz (Canton Zoug) and close to the
A4 motorway. The protective waterproofing layer is of gravel without any
landscaping. Over the years, mosses, lichens, herbs and grasses established
spontaneously as a result of localized damp conditions. In February 2007, we
laid 15 circles (19.6 m2)and6semi-circles(9.8m
2)of4–6cmthick‘ricoter’
to all of the roofs in the study; see Figure 18.2. On eight circles and two
semi-circles, we added 2-cm-thick turves; see Figure 18.3. The rest of the
ricoter ‘patches’ were sown with a small quantity of seed of Swiss indigenous
plants (annual and perennial herbs) with a high potential of water retention.
In June and July 2007, we added a layer of hay comprising alternate 3-cm deep
layers of freshly cut and dry hay to each of the five different turf circles. One
layer of 3-cm deep dry hay was applied to each of the four semi-circles; see
Figure 18.3 and 18.4.
Results
Use of the enhanced Rotkreuz roof by Vanellus vanellus
V. vanellus have returned to the Rotkreuz roof annually for about a decade,
and have produced about one to four clutches per year. The chicks hatched
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354 Nathalie Baumann and Friederike Kasten
Figure 18.2 Installation of circular patches of turf (2.5 cm deep) on the top of 4 cm
of ‘ricoter’, a Swiss compost recycling product developed for establishing rooftop
vegetation. The original ‘substrate’ on this roof was medium-sized gravel (2007,
N. Baumann).
successfully; in 2006 and 2007, they survived for 4–7 days – normally chicks
can only survive for 3–4 days on the remains of their egg yolk and without
finding food from elsewhere; if they do not do so, they die of starvation. In
2008, the chicks survived about 13 days – after that, only a few corpses were
found; it is assumed that the rest of the chicks were predated upon by raptors
or corvids (see Table 18.1).
Up to 2007, a minimum of 50 migrating individuals of V. vanellus were
frequently seen in autumn on the agricultural field, roosting in groups in front
of the building. Since June 2008, about 15 to 25 migrating individuals have
been observed while roosting on the roof.
Improvement of the vegetation on Rotkreuz roof with three
different methods
As described previously, in 2007 three vegetation methods, namely turf, seed
and hay, were applied for the improvement of the vegetation on a roof in
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Urban Habitats for Ground-Nesting Birds and Plants 355
Figure 18.3 Map of the Rotkreuz roof – the former gravel roof was revaluated with
a greening consisting of 15 circles and 6 semi-circles of vegetated surfaces. After two
vegetation seasons and despite a dry, hot spring in 2007, an interesting succession
of plants has developed since (Baumann).
Rotkreuz. As a result of the hot dry spring, by June 2007 (the end of the
V. vanellus breeding season) 90% of the vegetation and the substrate were dry,
despite being irrigated. Consequently, the vegetation was sparse and provided
little food and shelter for invertebrates, including insects and spiders. The
2008 survey showed a very good and beautiful layering of vegetation from near
the ground to 60 –80 cm high – typical meadow stratification. On assessment
using the Braun-Blanquet (Dierschke, 1994) method, it was found that
the vegetation cover of the patches was 90 –100% (30% grass species); see
Figure 18.5. Some plant species on these circular patches were as follows:
●Salvia pratensis (Meadow Clary)
●Campanula rotundifolia (Harebell)
●Stachys recta (Stiff Hedgenettle)
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356 Nathalie Baumann and Friederike Kasten
Figure 18.4 View of the roof in Rotkreuz just after the completion of the
vegetation improvement works (2007, N. Baumann).
●Holcus lanatus (Yorkshire Fog)
●Lolium multiflorum (Italian Ryegras)
●Arenatherum elatium (Tall Oatgrass)
Discussion
Vanellus vanellus on the Rotkreuz roof
Ground-nesting bird species such as C. dubius and V. vanellus are under
strong anthropogenic pressure in Switzerland, and to a lesser degree in other
European countries. Increasing urbanization has led to the continuing loss and
fragmentation of their breeding habitat (swamps, wetlands and grassland).
However, they have shown, time and again, that they can adapt to the changes
and to the urban landscape. V. vanellus, for example, chooses intensively
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Urban Habitats for Ground-Nesting Birds and Plants 357
Table 18.1 Overview of all roof sites from 2005 to 2008 – in the first row, the three
breeding seasons on the Rotkreuz roof are illustrated. The dark grey fields state that
in those years no observations were made, which is because we did not know the
sites by that time.
2005 2006 2007 2008
Adult birds
Nest found
Chicks hatched (all clutches)
Chicks fledged
Chicks age (relative days number)
Chicks found dead
Replacement clutches
Adult birds
Nest found
Chicks hatched (all clutches)
Chicks fledged
Chicks age (relative days number)
Chicks found dead
Replacement clutches
Adult birds
Nest found
Chicks hatched (all clutches)
Chicks fledged
Chicks age (relative days number)
Chicks found dead
Replacement clutches
Adult birds
Nest found
Chicks hatched (all clutches)
Chicks fledged
Chicks age (relative days number)
Chicks found dead
Replacement clutches
Roof sites:
Rotkreuz
Shoppyland
OBI
Steinhausen
Emmen
Hünenberg
Flughafen
Zürich Kloten
(ZH)
“Natural” Reference site
Choller
6(8) 6 # 0 05? 1 ? 8? ? ? ? 22 109 0 5 614
63954001 8 4 4 0 4 0 0 2 7 3 0 1
46; 13
4 (6)
5
3? ?
260
0 0031100104230700 21203000
4 ? 2 2 1 4 0 5 ? 0 2 3 0 7 1 4 (6) 2 9 0 10 1 2
4 (6) 2 7 3 40; 6 3 1
4442403
3 (4)
3 (4) 2 4 (?) 0 ?? 4 2
85 0411 4 0 4 5 1 4 0 4 311 135 (6)137 (8)15
managed areas of agricultural land and in recent years it has begun to utilize
flat vegetated roofs.
In 2008, the chicks of V. vanellus that hatched on the roof survived almost
13 days. Compared to 4 days in the previous years, the survival period
increased by three times. This shows that the improvement in the species
composition and structure of the vegetation and the good weather conditions
(wet and humid) during the summer of 2007 produced a relatively high insect
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358 Nathalie Baumann and Friederike Kasten
Figure 18.5 In July 2008, students from our department classified the plants and
their cover percentage on the Rotkreuz roof during their environment analytics
project week (from Chr. Groeflin (2008) with permission).
biomass – based on the assumption that the chicks were able to find food
sources elsewhere on the roof. However, because of the observation distance,
it was not possible to find out what they were eating. Autopsies of the stomach
content of chicks carried out by the Institute of Veterinary Bacteriology,
University of Zurich, failed to find any traces of insects in their guts. However,
the few corpses that were found were of 3- to 4-day-old chicks, which may
not have foraged but survived for a short time on the remains of the egg yolks.
It is impossible to draw conclusions from the autopsies because it is not clear
that the dead chicks starved to death. We assume that the other chicks, whose
bodies we could not find, were able to survive for 13 days because they found
some food.
An interesting observation was the use of the ponds by the adults and the
chicks. On land where chicks are rarely seen drinking at temporary pools or
small ponds they apparently need and use water on the roofs for drinking,
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Urban Habitats for Ground-Nesting Birds and Plants 359
for cooling and maybe for finding some invertebrates (for example, midge
larvae, Tubifex, etc.). This is a new parameter in our research considerations
and we hope to make more conclusive observations in 2009. There is little
data about the need for water, either on the ground or on roofs. Kooiker
(2000) mentioned that V. vanellus colonies have had a good breeding success
in habitats with no or only short vegetation and the absence of water bodies
such as small ponds, pools, ditches and damp mud surfaces.
The factors that control the survival of V. vanellus chicks and their relative
importance remain unknown. We assume that these factors are likely to
include weather conditions, limited vegetation cover and, therefore, a low
biomass of plants and invertebrates. The adult birds were observed wanting
to leave the roof – the parent birds were seen flying up and down trying to
encourage the chicks to move to another more suitable foraging site, which is
impossible for them to do from a roof top. This behaviour is similar to ground
observations by Kooiker and Buckow (1997), who found that adult V. vanellus
with chicks change sites if the vegetation becomes too high and/or if there is
insufficient food.
V. vanellus are remarkably faithful to a breeding site; consequently, if they
start to breed on a flat , they will return despite being unsuccessful in rearing
the first and subsequent broods. Another important observation is that groups
of 15–25 birds use the Rotkreuz roof from June to September as a roosting
site on their migration south – it is the only roof site where we have seen this
behaviour.
Establishment of vegetation on the Rotkreuz roof
In summary, the techniques used are valuable in establishing or enhancing
grassland vegetation on roofs. There was no displacement despite strong
winds. The thickness of the turf or hay layer plays a determinant role in the
establishment of the vegetation. In addition, hay has a positive effect on
the development of vegetation, particularly during hot weather in springtime.
The transportation of hay to roofs is slightly complex, but not impossible
(Tausendpfund, 2008).
In 2008, after only two growing seasons of the improved habitats exercise,
90–100% plant cover had been established using the hay method, which is a
great success, considering the harsh conditions on a roof. Unfortunately, in
2007, April and May were dry and hot months; consequently about 90% of
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360 Nathalie Baumann and Friederike Kasten
the established vegetation dried out just at the time the birds were breeding
and the chicks hatching. As a result of the wet summer in 2007, the vegetation
recovered well and plant growth improved in 2008 with a good vegetation
biomass with some faunal food source (insects, spiders and other small
animals), which is particularly important for young precocial birds.
The usefulness of applying or establishing vegetation on roofs with fresh
or dry hay is not well known. In this process, grass is used together with
ripe seeds from surrounding areas in order to create a meadow-like roof.
It has been proved from use at ground level that this method offers a very
good alternative to the use of commercial seed mixes. The method is also
beneficial in providing a nucleus of invertebrate species, which is important
for the development of the roof-meadow as a natural habitat. The success of
the natural seeding mostly depends on the species, composition of the hay and
on the time when it was cut and applied. In addition, displacement of the hay
from the roof by the wind or even the reverse – the transfer, by wind, of seed
from the surrounding area onto the roof – may play a role in the composition
of the roof vegetation.
The fresh hay method appears to be a good method of establishing rooftop
vegetation. When applied on a layer of 3–4 cm thickness, the plant species
grow well. The mulch also acts as a humus basis, retaining water and providing
a habitat for insects, which is important on roofs in hot and dry season.
Because the trials only started in 2007, we are not yet able to present (in this
chapter) the comprehensive results of all the main areas of our research.
Perspectives: green roofs, a suitable breeding habitat?
It is not yet possible to determine whether a sustainable habitat can be created
on roofs using these new techniques or whether it is better to create and
manage new habitats on the ground. Nevertheless, it is important to create
and enhance habitats on the ground but it is not always possible to do so.
In such cases, grassland and other habitats can be created on extensive flat
roofs to compensate for or supplement habitats on the ground by providing,
amongst other things, opportunities for breeding areas for ground-nesting
birds. To do this will involve the development of further and better procedures
for the development of rooftop vegetation. In the following years, we intend
to examine many or all of these issues.
In summary, the improvements in the layout of the roof vegetation allow
us to respond rapidly to changing weather conditions, which is an influential
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Urban Habitats for Ground-Nesting Birds and Plants 361
parameter in determining the successful establishment of the plant and animal
biomass. The weather conditions from April to July 2008 were almost perfect.
We assume that more broods will be observed and that the chicks will survive
longer – at a new green roof site (not described in this chapter); three chicks
even fledged successfully. On the first day after the young birds had fledged,
we were only able to find one of the three – it was seen with its parents in an
agricultural field near the roof site. After 3 more days, we were unable to find
either the remaining young bird or the adult birds. We assume that the first
two of the three young birds were caught by a ground-living predator that
frequently hunts in peri-urban areas. The same fate may have been suffered
by the third young bird. However, none of the corpses of the three young
birds were found, consequently; it is equally plausible to assume that one or a
combination of the young birds flew away. With this ‘milestone’ we can prove,
for the first time, that sufficient food for the chicks of ground-nesting birds
can be provided in roof vegetation if the conditions on the roof are suitable
and good. That means that the vegetation and some areas on the roof can
store water and keep the substrate humid – we consider that this is the key,
finding enough substrate to enable invertebrates to undergo their life cycles at
an optimum rate. The roofs can be improved as breeding habitats for birds by
the creation of humid areas using irrigation during the summer months and
on dry, hot days in order to attract sufficient insects.
The 2009 season is likely to be interesting; as a result of the experiences and
observations during the previous years, we will be able to concentrate on and
give greater attention to the effects of the improvements on plant and animal
biomass and their impact on hatching of the eggs and survival of the chicks.
Acknowledgements
We are grateful to the Federal Office for the Environment (FOEN), to all the
different partners (substrate producers, companies, building owners, commu-
nity and canton offices, etc.), and private persons who joined, participated and
supported us in this project and made it possible for us to realize the project
successfully.
References
Baumann, N. (2006) Ground-nesting birds on green roofs in Switzerland: preliminary
observations. Urban Habitats, 4(1), 37–50, ISSN 1541 –7115.
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Brenneisen, S. (2003) ¨
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gen – Bedeutung f¨
ur den Arten- und Naturschutz und die Stadtentwicklungsplanung.
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at Basel. Basel, Switzerland.
Clergeau, P., Croci, S., Jokim¨
aki, J., Kaisanlahit-Jokim¨
aki, M.-L. & Dinetti, M.
(2006) Avifauna homogenisation by urbanisation: analysis at different European
latitudes. Biological Conservation, 127, 336–344.
Dierschke, H. (1994) Pflanzensoziologie: Grundlagen und Methoden. Ulmer, Stuttgart.
K¨
ohler, M. (2006) Green roofs and biodiversity: long-term vegetation research on two
extensive green roofs in Berlin. Urban Habitats, 4(1), 3 –26, ISSN 1541-7115.
Kooiker, G. (2000) Kiebitzbrutpl¨
atze in Mitteleuropa: Entscheidungen in schwieriger
Situation. Der Falke, 47, 338–341.
Kooiker, G. & Buckow, C.V. (1997) Der Kiebitz: Flugk¨
unstler im Offen Land.Aula
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[retrieved 30 May 2008].
Tausendpfund, D. (2008) Dachbegr¨
unung mit Heumulchverfahren. G’plus, 11, 34 –35.
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Queries in Chapter 18
Q1. We have shortened the Running head. Please confirm if it is fine.