Conference PaperPDF Available

Using high-resolution aerial imagery to assess populations of wintering waterbirds

  • IfGDV Germany
4th International Conference on
Progress in Marine Conservation
in Europe 2015
Proceedings of the Conference
Stralsund, Germany, 14 - 18 September 2015
Henning von Nordheim
Katrin Wollny Goerke
Cover picture: Conference poster M. Putze, C. Pfützke, S. Gust, F. Graner, S. Bär)
Editors’ addresses:
Prof. Dr. Henning von Nordheim Federal Agency for Nature Conservation (BfN)
Marine Nature Conservation Department, Isle of Vilm
18581 Putbus, Germany
Katrin Wollny-Goerke meeresmedien
Kakenhaner Weg 170
22397 Hamburg, Germany
Scientific Supervision:
Prof. Dr. Henning von Nordheim Department II 5 „Marine Nature Conservation“
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Bonn, Germany 2016
Using high-resolution aerial imagery to assess populations of
wintering waterbirds
Timothy Coppack1, Alexander Weidauer2, Axel Schulz2, Görres Grenzdörffer3
1 
2 Institute of Applied Ecology GmbH (IfAÖ), Germany
3 University of Rostock, Germany
1 Introduction
Birds inhabit heterogeneous environments across a wide range of temporal and spatial scales.
Migratory waterbirds in particular are highly reactive to changes in climate, food availability and
the marine environment.
The Baltic Sea with its many protected areas holds large numbers of moulting and wintering
waterbirds. While some of the species are listed as “vulnerable” under Annex I of the EU Birds
Directive, e.g. Red-throated Diver (Gavia stellata), most of the waterfowl species listed under
Annex II are currently among those species showing the strongest overall population declines
(European Commission 2015). The Long-tailed Duck (Clangula hyemalis) has recently been
uplisted to “vulnerable” because of an apparent rapid decline detected in the wintering popu-
lation in the Baltic Sea since the 1990s (BirdLife International 2015, see also BelleBauM et al.
The Natura 2000 network, comprising Special Protection Areas (SPAs) under the EU Birds
Directive and Special Areas of Conservation (SACs) under the EU Habitats Directive, now
covers over 4 % of Europe’s seas (European Commission 2015). SPAs are designated ac-
cording to criteria such as “1 % of the population of listed vulnerable species” or “wetlands of
international importance for migratory waterfowl”. These criteria are currently based on obser-
vational census data collected during ship-based and aerial transect surveys (e.g. MarKOnes
et al. 2015).
Seasonal or monthly surveys of seabirds and waterbirds represent snapshots (random
samples) of local populations that form part of unknown meta-populations. The robustness
        
technique, the design and level of spatial coverage, and on the timing of the surveying effort re-
lative to the phenology of a given species. Observational methods introduce further uncertainty
to the resulting population estimates. Ships (sChWeMMer      
(KuleMeyer et al. 2011) disturb sensitive bird species and thus negatively affect detection rates.
Furthermore, theoretical models correcting for distance-related observer-bias generally assu-
me random distribution of individuals. This is evidently not the case in benthivorous sea ducks
that aggregate in response to the accessibility of their invertebrate food. A biased detection in
estimates with far-reaching consequences for conservation policy.
Recent developments in digital aerial imagery allow a less invasive and safer census of marine
wildlife, thereby solving major problems with previous survey methods (BuCKlanD et al. 2012,
Taylor et al. 2014, COPPaCK et al. 2015). Survey data resulting from orthogonal digital images
no longer need to be corrected for distance-related detection bias. The recent switch from ana-
acquisition, data processing and archiving require expensive equipment and experienced staff,
which currently sets limits to the affordable number of surveys per annual cycle. Thus, there is
an urgent need to consider trade-offs between image quality (resolution, signal-to-noise ratio)
In this pilot study, we carried out experimental trials based on gapless, vertical imagery of a
sub-sampling to determine the minimum coverage required for quantifying aggregations of
waterbird species relevant to marine conservation and spatial planning, i.e. Common Scoter
(Melanitta nigra), Common Eider (Somateria mollissima), and Long-tailed Duck.
2 Methods
The study area of 46.75 km² was situated in the Bay of Wismar, western Baltic Sea (SPA, UM
M-V 2006), and covered a water-depth gradient ranging from 3 m in the south to about 20 m
in the north. On March 12 2014, a complete survey of the area was performed in 4 h with a
  
included 33 parallel transects of 8.5 km length each oriented in north to south direction and
covering the entire study area. Digital images were collected and stored with a PhaseOne
dicularly into the hatch of the aircraft. The aircraft’s position was continuously logged by GPS
(Leica GPS1200), which automatically synchronized the release mechanism of the camera.
Each photo contained 10328 by 7760 pixels and covered an image footprint of 200 x 150 m
at 2 cm ground sample distance (GSD), i.e. each pixel represents an area of 2 cm × 2 cm at
   -
ween consecutive photos. Image overlap between neighbouring transects lay at around 20 %.
The survey took place under suitable weather conditions (wind speed < 5 m / s, sea state < 3,
visibility > 5 km).
GIS environment for further editing, taking the overlapping areas and areas affected by glare
into account (cf. steFFen 2014, COPPaCK et al. 2015). The remaining image strips were visually
screened with a purpose-programmed viewer software by a single trained person. Each detec-
The region of interest was grouped into cells with 38 rows and 49 columns in an east-to-west
statistical parameters over the variation of sampling experiments with a given effort (for ex-
ample 50 %, 33 %, 25 %, 12 %, etc.). An effort of 25 % (1/4), for example, provides 4 variants
for sampling the region of interest and yields 4 average density values, an effort of 12,5 % (1/8)
yields 8 values, and so forth. These spectra of densities over effort were compared with the
accurate density values determined at 100 % coverage (i.e. for Common Scoter 93 indiv./km²,
for Common Eider 80 indiv./km², for Long-tailed Duck 43 indiv./km², cf. Figure 1).
In this experiment, we only varied coverage and did not test the outcomes of different sampling
3 Results
Figure 1 shows the relationship between simulated survey effort and estimated densities for
the three duck species Common Scoter, Common Eider, and Long-tailed Duck. A stepwise
reduction of sampling effort (spatial coverage) led to an increase of the variation of calculated
densities. The increase of variation was evident in all species below 50 % (1/2) of total covera-
ge. This effect of sampling effort on the survey outcome was independent of the orientation of
Figure 1:
Top: Grid maps of three sea duck species (Common Eider, Long-tailed Duck, Common Scoter) based on gapless
aerial photos taken on March 12 2014 in the German Baltic Sea (Bay of Wismar).
on), which simulated different proportions of spatial coverage from 100 % (1/1) to 10 % (1/10). The dotted horizon-
tal lines show the average densities found at 100 % coverage. The graphs show that sampling efforts below 25 %
may result in systematic under- and over-estimations of population density by factors > 2.
4 Discussion
determined and spatially distinct population of wintering waterbirds. A simulated reduction of
such that population densities were either overestimated or underestimated with decreasing
survey effort. This result emphasises the importance of adjusting areal coverage to the expec-
ted frequency distribution of birds before commissioning dedicated aerial surveys. The effect
of areal coverage on the quantitative outcome of a survey is predicted to be especially strong
when the species of interest is non-randomly distributed, like in our case.
Our study has major implications for the future design and implementation of aerial digital
surveys for assessing populations of wintering waterbirds in protected areas. Reducing spatial
coverage for economic reasons and following a traditional transect design (continuous series
of images collected along widely spaced trajectories) increases the chance that a SPA or ag-
gregation of birds is chronically undersampled. Through concentrating and equally spacing
 
values and overall probability densities into account, the relative quantity of images, survey
time and costs could be reduced, while the statistical power and biological meaning of the
surveys would increase.
The minimum technical and methodological requirements for carrying out digital aerial surveys
are subject to ongoing basic research. A sound conceptual framework based on further empiri-
cal trials, e.g. by comparing simultaneous ship-based and aerial observations, will be decisive
for the calibration of observational and camera-based survey techniques in order to evaluate
the backlog of existing data and population estimations.
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Full-text available
The European Red List of Birds builds on two earlier assessments of the population status of all species at European level: the 'Birds in Europe' volumes. The main objective was to assess the status of all European bird species, for the first time using data reported by EU Member States under Article 12 of the EU Birds Directive, together with comparable data reported by NGOs and other collaborating experts from the rest of Europe. For every bird species native to Europe, apart from national population and trend information, the following data were compiled in the form of species factsheets: species' taxonomic classification, map of distribution in Europe, ecology and habitat preferences, major threats, conservation measures and key literature references. At the European regional level, 13% of bird species (67 species) were assessed as threatened, with 2% (10 species) Critically Endangered, 3% (18 species) Endangered, and 7% (39 species) Vulnerable. A further 6% (32 species) were assessed as Near Threatened (Figure 3a). Within the EU 27, 18% of bird species (82 species) were threatened, with 2% (11 species) Critically Endangered, 4% (16 species) Endangered, and 12% (55 species) Vulnerable, and a further 6% (26 species) were Near Threatened. The results of the work contribute to regional conservation planning through provision of an up-to-date dataset reporting the status of European birds, identification of the major threats to these birds, and proposals of mitigating measures and conservation actions to address them.
Conference Paper
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Die naturschutzfachliche Bewertung menschlicher Aktivitäten auf See erfordert eine zunehmend verlässliche Datengrundlage. Die Umsetzung von Windparkprojekten im Offshore-Bereich der deutschen Nord- und Ostsee muss laut Vorgaben der Genehmigungsbehörde von großflächigen Erfassungen von Seevögeln und Meeressäugern begleitet werden, um potenzielle Auswirkungen (Habitatverlust, Bestandseinbußen) auf diese Schutzgüter bewerten zu können. Bestandteil der methodischen Richtlinien waren bisher visuelle Zählungen mittels Kleinflugzeug. Die hierbei zur Artbestimmung notwendige niedrige Flughöhe kann jedoch bei störungsempfindlichen Vogelarten zur weiträumigen Flucht vor dem Flugzeug und damit zu Schwierigkeiten bei der Erfassung führen. Im Bereich bestehender Windparks ergeben sich zudem erhebliche Sicherheitsrisiken für den Menschen. Einen Ausweg bietet die Erfassung der Meeresoberfläche aus deutlich größerer Flughöhe mit hochauflösenden, digitalen Kameras. Vor dem Hintergrund der zu erfüllenden Monitoringaufgabe wurde eigens ein Luftbildsystem konfektioniert, welches aus einer Flughöhe von > 400 m orthogonale, georeferenzierte Bilddatensätze generiert. Zwei Mittelformatkameras vom Typ IXA180 PhaseOne auf einer Stabilisationsplattform der Firma GGS Speyer liefern bei einer Brennweite von 110 mm eine abgedeckte Streifenbreite von ca. 400 m bei einer Bodenauflösung von 2 cm. Durch das visuelle Screening der aufbereiteten georeferenzierten Luftbilder mithilfe speziell entwickelter Softwareanwendungen wird jedem biologischen Signal eine Position im GIS zugeteilt, was eine Zuordnung zu vordefinierten Betrachtungsbereichen (z. B. Rasterzellen) bei geostatistischen Auswertungen erleichtert. Zudem wird ein Ausmessen von biologischen Objekten möglich, was bei der Artbestimmung zusätzliche Indizien liefert.
Full-text available
Abundance of Long-tailed Ducks Clangula hyemalis wintering in the Pomeranian Bay was monitored between 1988 and 2014, using both ship-based and aerial surveys and cor-recting for distance dependent detection. Aerial surveys were conducted using an im-proved transect division and a double observer design to estimate detection probability near the transect line. As the latter probability was considerably below 1, we applied an additional correction factor for observer efficiency. After correcting for observer effi-ciency in aerial surveys, the two methodological approaches yielded similar densities, though an apparent underestimation in aerial surveys warrants further cross-validation. Density estimates from both platforms were merged for further analysis. After reaching peak levels in 1992 and 1993, Long-tailed Duck winter densities in the Pomeranian Bay declined by 82% until 2010. This decline was part of an overall decline in numbers throughout the Baltic Sea. An apparent increase since 2010, which was likely due to local ice-induced movements, indicates that habitats in the study area may still support high densities today.
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Abstract Marine aerial surveys are designed to maximize the potential for detecting target species. Collecting data on different taxa from the same platform is economically advantageous but normally comes at the cost of compromising optimal taxon-specific scanning patterns and survey parameters, in particular altitude. Here, we describe simultaneous visual and photographic sampling methods as a proof of concept for detecting large whales and turtles from a single aircraft, despite very different sighting cues. Data were collected for fishing gear, fish, sharks, turtles, seals, dolphins, and whales using two observers and automated vertical photography. The photographic method documented an area directly beneath the aircraft that would otherwise have been obscured from observers. Preliminary density estimates were calculated for five species for which there were sufficient sample sizes from both methods after an initial year of data collection. The photographic method yielded significantly higher mean density estimates for loggerhead turtles, ocean sunfish, and blue sharks (p 0.05), two of the largest species included in the analysis, which are relatively easy to detect by both methods. Although postflight manual processing of photographic data was extensive, this sampling method comes at no additional in-flight effort and obtains high-quality digital documentation of sightings on the trackline. Future directions for this project include automating photographic sighting detections, expanding the area covered by photography, and performing morphometric measurement assessments.
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1. Aerial seabird surveys are often conducted so that changes in abundance may be monitored. For example, large-scale offshore wind farms are proposed for UK waters, and surveys are currently being conducted to quantify numbers and distribution ahead of construction. 2. Technological advances mean that strip transect surveys may now be conducted, using digital methods. We address survey design and data analysis issues for such digital surveys, contrasting them with visual aerial line transect surveys. 3. We also explore the relative performances of the methods for estimating the size of a large aggregation of common scoters in Carmarthen Bay, Wales. We found that abundance estimates from two digital methods were closely comparable, while estimates from visual aerial surveys were appreciably lower. 4. Synthesis and applications. Efficient survey methods to quantify abundance and distribution of seabirds are needed, to assess change arising from climate change, or developments such as the construction of large-scale offshore wind farms. The traditional survey methods are visual surveys conducted along transects from ships or aircraft. Digital video and stills surveys can be conducted from aircraft flying sufficiently high to avoid disturbance, while still being able to detect and identify seabirds. Given the rapid technological developments, we expect digital surveys largely to replace visual surveys for seabirds in offshore regions.
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Most anthropogenic influences on marine ecosystems, except for river- or terrestrial-borne pollution, involve some sort of vessel activity. Increasing anthropogenic activities mean that many countries are being forced to develop spatial planning schemes, while at the same time implementing conservation sites for sensitive species at sea. The effects of ship traffic on seabirds sensitive to human disturbance are currently too poorly understood to allow for the development of proper planning and conservation guidelines. We therefore used aerial surveys and experimental disturbance to elucidate the effects of passing ships on the distribution patterns, habitat loss, and species-specific flight reactions of birds, as well as the potential for habituation. Loons (Gavia spp.) showed clear avoidance of areas with high shipping intensity. Flush distances of four sea duck species differed significantly, with the longest distances recorded for Common Scoters (Melanitta nigra) and the shortest for Common Eiders (Somateria mollissima). Flush distance was positively related to flock size. Among all the sea duck species studied, the duration of temporary habitat loss was longest for Common Scoters. We found indications of habituation in sea ducks within areas of channeled traffic. However, it is questionable if habituation to free-ranging ships is likely to occur, because of their unpredictable nature. We therefore recommend that spatial planning should aim to channel ship traffic wherever possible to avoid further habitat fragmentation and to allow for habituation, at least in some species. Information on the effects of shipping on other seabird species and during different periods of the year is urgently needed, together with information on the effects of different types of boats, including recreational and fishing vessels.
The State of Nature in the European Union -Report on the status of and trends for habitat types and species covered by the Birds and Habitats Directives for the 2007-2012 period as required under Article 17 of the Habitats Directive and Article 12 of the Birds Directive
  • European Commission
eurOPean COMMissiOn (2015). The State of Nature in the European Union -Report on the status of and trends for habitat types and species covered by the Birds and Habitats Directives for the 2007-2012 period as required under Article 17 of the Habitats Directive and Article 12 of the Birds Directive. Report from the Commission to the Council and the European Parliament, Brussels.
Managementplan für das FFH-Gebiet DE 1934-302 Wismarbucht (gleichzeitig teilweise Vogelschutzgebiet DE 2034- 401 gemäß Vogelschutz-Richtlinie) Referat Landschaftsplanung
UM M-V (Umweltministerium Mecklenburg-Vorpommern) (2006). Managementplan für das FFH-Gebiet DE 1934-302 Wismarbucht (gleichzeitig teilweise Vogelschutzgebiet DE 2034- 401 gemäß Vogelschutz-Richtlinie). Referat Landschaftsplanung, Management der Natura 2000 Gebiete, Schwerin.
  • C Kulemeyer
  • Schulz
  • Weidauer
  • K Schleicher
  • T Foy
  • Coppck
KuleMeyer, C., sChulZ, a., WeiDauer, a., röhrBein, v., sChleiCher, K., FOy, t., grenZDörFFer, g., COPPCK, t. (2011). Georeferenzierte Digitalfotograie zur objektiven und reproduzierbaren Quantiizierung von Rastvögeln auf See. Vogelwarte 49: 105-110.
sChWeMMer h., garthe s
  • Markones N
  • K Borkenhagen
MarKOnes n., guse, n., BOrKenhagen, K., sChWeMMer h., garthe s. (2015). Seevogel-Monitoring 2014 in der deutschen AWZ von Nord-und Ostsee. Bericht für das Bundesamt für Naturschutz, Vilm.