Thomas K. Gottschalk

Thirty years of analysing and modelling avian habitat relationships using satellite imagery data: a review

The application of remote sensing and Geographic Information Systems (GIS) technologies provides powerful tools when used to investigate wildlife and its habitat for an analysis or modelling approach. In this context, birds have been of great and progressive value as biological and environmental indicators. In order to learn about the common approaches used—its methods, processing steps, trends, advantages and challenges—over 120 representative publications of the last 30 years that made use of satellite images for avian applications have been reviewed. The reviewed studies have shown that GIS‐based analyses of satellite and bird data have been well established for efficient ecosystem descriptions and species modelling within a large range of scales and habitats. In order to improve the quality of inference and for comparative analyses, it is recommended that further studies are documented in detail. Also, in order to verify and improve the obtained results, additional ground data on the main structure of the vegetation relevant to the bird species in question are usually necessary. Satellite‐based remote sensing applications in ornithology could be used increasingly for assisting in habitat evaluation, habitat modelling and monitoring programmes and in achieving overall wildlife conservation and management objectives effectively. This is especially true for remote regions of the world that are difficult to access where few habitat studies have been undertaken to date but whose study is urgently needed.

Impact of agricultural subsidies on biodiversity at the landscape level

Agricultural management is a major factor driving the change of faunal richness in anthropogenic landscapes. Thus, there is an urgent need to develop tools that allow decision-makers to understand better intended and unintended effects of agricultural policy measures on biodiversity. Here we demonstrate the potential of such a tool by combining a socio-economic model with the biodiversity model GEPARD to forecast the response of bird and carabid species richness to two scenarios of agricultural subsidies: (1) subsidies based on production levels and prices and (2) direct income support that is independent of production levels. We focussed on farmland of the Lahn-Dill area, Germany, as an example of European regions with low intensity farming. GEPARD predicts faunal richness and is based on multi-scaled resource-selection functions. Under both scenarios the area of predicted losses in species richness of birds and carabids was larger than the area of predicted gains in species richness. However, the area with predicted losses of avian richness was smaller under the direct income support scenario than under the production-based subsidy scenario, whereas the area with predicted losses of carabid species richness was smaller under the production-based subsidy scenario than under the direct income support. Yet locally, richness gains of up to four species were predicted for carabids under both scenarios. We conclude that the sometimes contrasting and heterogeneous responses of birds and carabids at different localities suggest the need for spatially targeted subsidy schemes. With the help of the GIS-based approach presented in this study, prediction maps on potential changes in local and regional species richness can be easily generated.

New insights into the consequences of post-windthrow salvage logging revealed by functional structure of saproxylic beetles assemblages.

Windstorms, bark beetle outbreaks and fires are important natural disturbances in coniferous forests worldwide. Wind-thrown trees promote biodiversity and restoration within production forests, but also cause large economic losses due to bark beetle infestation and accelerated fungal decomposition. Such damaged trees are often removed by salvage logging, which leads to decreased biodiversity and thus increasingly evokes discussions between economists and ecologists about appropriate strategies. To reveal the reasons behind species loss after salvage logging, we used a functional approach based on four habitat-related ecological traits and focused on saproxylic beetles. We predicted that salvage logging would decrease functional diversity (measured as effect sizes of mean pairwise distances using null models) as well as mean values of beetle body size, wood diameter niche and canopy cover niche, but would increase decay stage niche. As expected, salvage logging caused a decrease in species richness, but led to an increase in functional diversity by altering the species composition from habitat-filtered assemblages toward random assemblages. Even though salvage logging removes tree trunks, the most negative effects were found for small and heliophilous species and for species specialized on wood of small diameter. Our results suggested that salvage logging disrupts the natural assembly process on windthrown trees and that negative ecological impacts are caused more by microclimate alteration of the dead-wood objects than by loss of resource amount. These insights underline the power of functional approaches to detect ecosystem responses to anthropogenic disturbance and form a basis for management decisions in conservation. To mitigate negative effects on saproxylic beetle diversity after windthrows, we recommend preserving single windthrown trees or at least their tops with exposed branches during salvage logging. Such an extension of the green-tree retention approach to windthrown trees will preserve natural succession and associated communities of disturbed spruce forests.

Increased energy maize production reduces farmland bird diversity

Producing energy crops as an alternative to fossil fuels in order to reduce CO2 emissions will lead to large‐scale changes in agricultural landscapes. Here, we quantify the potential impact of an increase in maize fields on the diversity of farmland birds by means of high resolution (25 × 25 m) land‐use scenarios. We generated scenarios in which the area of maize production in Germany increases from presently 2.6 to 2.9, 3.6 and 4.3 million ha, corresponding to the energy crop production targets of the German Renewable Energy Act for the years 2020, 2035 and 2050. To test the mitigating potential of conservation measures, each scenario was generated in a standard version and a landscape protection version, with the latter excluding valuable farmland areas from being converted into maize fields. Nine species of farmland birds belonging to the governmental indicator scheme for sustainable land‐use in Germany were modelled for the six nation‐wide scenarios. The models predicted that only the Northern Lapwing and the Little Owl might profit from extended maize production. Despite this, the total number of breeding pairs of the indicator species was predicted to decline by about 0.4 million breeding pairs in the most intensive scenario. Protection of valuable farmland did not mitigate these negative effects in the models. Our findings suggest that increased production of energy crops conflicts with conservation of biological diversity.

Comparison of distance sampling and territory mapping methods for birds in four different habitats

Distance sampling (DS) and territory mapping (TM) are globally applied bird survey techniques. However, specifically designed studies comparing results of both methods in different habitats in the framework of a scientific experiment have rarely been conducted. To provide a more generalized guidance for the field surveyor, here we evaluated estimates of bird abundances and number of bird species in four different habitats (broad-leaved forest, coniferous forest, open woodland and farmland) in central Germany. Abundances were estimated in parallel by TM and DS in 2006 and 2008, following standard protocols. Detection probability differed significantly among habitats and species. Density estimates by DS were in total 24% lower than those estimated by standardized TM. While the number of bird species detected with both methods was approximately the same, the estimated abundances of 15 bird species showed significant differences. Increasing the number from two to four and five registrations to count a territory by using TM decreased the density on average about 28 and 42%, respectively. Using standardized TM resulted in an overestimation of abundances of species showing a high detection probability. In contrast, DS estimated very high densities for species that had a very low detection probability. In fact, a highly negative correlation was found between the density estimated by DS and the detection probability. Using standardized TM and setting a fixed number of registrations before a location qualifies for a bird territory cannot compensate for the large differences in species detectability. Instead, the number of registrations required to count a territory should be adjusted to differences in detection probabilities and seasonal activity. From our results we can recommend a mean of four registrations if eight visits were conducted to count a territory. However, the lack of any statistically-based quality assessment reduces the serious usability of TM for estimating densities for science-based management application, whereas, the clear advantage of DS is that it provides error estimates and considers differences in species detectability.ZusammenfassungDistance Sampling (DS) und Revierkartierung gehören zu den verbreitetsten Erfassungsmethoden von Vogelbeständen weltweit. Bisher gibt es kaum Studien bei denen im Rahmen eines wissenschaftlichen Experiments beide Methoden parallel durchgeführt und die Ergebnisse verglichen wurden. Ziel der im Jahr 2006 und 2008 im Hohen Vogelsberg, Hessen durchgeführten Untersuchung war es deshalb, jeweils die Artenanzahl und die Abundanzen von Vögeln sowohl mit DS als auch mit der Revierkartierung in vier unterschiedlichen Lebensräumen (Laubwald, Nadelwald, Halboffenland und Offenland) standardisiert zu erfassen und zu vergleichen. Die Erfassungswahrscheinlichkeit unterschied sich deutlich zwischen den Lebensräumen und zwischen den Vogelarten. Die Dichten, die mit Hilfe von DS erfasst wurden, fielen im Durchschnitt um 24% niedriger aus im Vergleich zu den mit der Revierkartierung ermittelten Dichten. Während die Anzahl der ermittelten Arten bei beiden Methoden in etwa gleich war, zeigten die Abundanzen von 15 Arten signifikante Unterschiede. Bei der standardisierten Revierkartierung wurde ein Revier nur dann gezählt, wenn mindestens zwei Registrierungen der Art erfolgten. Steigert man die Anzahl der notwendigen Mindestregistrierungen auf vier bzw. fünf reduzierte sich die Dichte im Durchschnitt um 28% bzw. 42%. Die standardisierte Revierkartierung führte zu einer Überschätzung der Bestände von Vogelarten mit einer hohen Erfassungswahrscheinlichkeit. Im Gegensatz hierzu wurden mit DS sehr hohe Dichten für Arten mit geringer Erfassungswahrscheinlichkeit ermittelt. Dies verdeutlicht die festgestellte negative Korrelation zwischen Dichte und Erfassungswahrscheinlichkeit. Die Verwendung der Revierkartierung mit einer fixen Anzahl von Mindestregistrierungen zur Zählung eines Reviers wird den unterschiedlichen Erfassungswahrscheinlichkeiten zwischen den verschiedenen Vogelarten nicht gerecht. Daher empfiehlt sich ein artspezifisches Vorgehen unter Berücksichtigung der Erfassungswahrscheinlichkeit und der saisonalen Aktivität. Unsere Ergebnisse zeigen, das zur Wertung eines Reviers im Durchschnitt vier Registrierungen eines Vogels bei acht Begehungen notwendig sind, um realistischere Abundanzen zu erhalten. Das Fehlen jeglicher statistischer Angaben zur Bestimmung der Erfassungsgüte bei der Revierkartierung reduziert deren Eignung, um wissenschaftlich fundierte Aussagen zu erhalten. DS bietet dagegen den großen Vorteil, dass es zu jeder berechneten Abundanz Konfidenzintervalle und den jeweiligen Fehler liefert.

Efficient Placement of Nest Boxes for the Little Owl (Athene noctua)

Abstract The use of artificial nest boxes to bolster populations of endangered cavity-nesting birds has increased significantly, but spatial variation of nest-box occupancy rates and breeding success within a nest-box population has been little studied. In a case study with 798 Little Owl (Athene noctua) nest boxes established in central Germany, we analyzed the dependence of occupancy rate and breeding success on the characteristics of the surrounding habitat. The analysis focused on two aspects of general concern for nest-box management: (1) whether nest boxes were occupied for breeding or were left unoccupied, and (2) whether Little Owls had different reproductive rates, depending on the location of nest boxes. A high resolution (1 × 1 m) land-use map was used to analyze species-habitat relationships, and Generalized Linear Mixed Models were used to predict suitable nest-box locations. During the period from 2004 to 2006, 544 (68%) of the nest boxes were never occupied, 144 (18%) housed birds with low breeding success and only 108 (14%) housed pairs that produced more than 2.35 nestlings annually, a reproductive rate thought necessary for population stability. Nest boxes were more likely to be occupied if they were located near orchards, at lower altitude, and in areas of higher densities of fields and less forest. Higher breeding success was associated with fallow fields and field margins, and with greater distance to roads and forests. Our results suggested that the efficiency of this nest-box program could be substantially increased if unoccupied nest boxes were relocated to sites where occupancy is more likely, and if unproductive nest boxes were relocated to locations that would enhance breeding success.

A GIS-based model of Serengeti grassland bird species

In this study we assess possible benefits of using satellite sensor data in large-scale landscape ecology. The study was conducted on the Serengeti Plains, Tanzania, combining (1) records from a bird survey, (2) local measurements of vegetation structure and precipitation, and (3) a habitat map derived from a Landsat satellite image classification. The question of whether ground-based or satellite data explained more of the species-environment relationships was explored by means of multivariate regression. On average across all 62 bird species recorded, the combination of satellite-based and ground-based data improved explained variance (R2 = 0.26), as compared to satellite sensor data, or ground-based data alone (R2 = 0.18 and 0.21, respectively). In spite of this low level of explained variance in the regressions, a classification of bird species according to utilised parameter space yielded reasonable results. Satellite image data seem to be suited to this kind of investigation.

The Problems of Recording Bird Numbers in the Breeding Season as Pairs

Abstract As more and more species become threatened, the need to assess population sizes accurately in order to facilitate effective management actions increases. There is an extensive literature on counting birds, but no consensus on the most appropriate units in which to record the results. To stimulate discussion on the use of “number of pairs” for estimating bird population size we review some of the main problems and difficulties. Some counts, especially of seabirds, give total numbers, whereas breeding season counts of songbirds often record territories or, less frequently, numbers of nests. The use of different units complicates comparisons, for example between non-breeding and breeding populations. In many populations there are non-breeding individuals (including immatures, helpers or those who have failed to secure a mate or a territory) that may be hard to distinguish from those that are breeding. Some of the last may even be more conspicuous than paired birds. The proportion of such, for most species, is unknown. In some species, males may attract more than one female. But detailed knowledge of demography is lacking for many species, especially in the tropics. Nest counts can also present problems as some species may make more than one nest. On the other hand, all individuals alive in the breeding season may potentially contribute to future generations and thus, for most purposes, it is preferable to record the number of all individual birds. Wherever known, estimation of the proportion of birds breeding could be added, and we suggest that a global database of such information would be valuable.

Habitat preferences and status of an elusive forest species: the Oberländer's Ground-Thrush Zoothera oberlaenderi in Uganda

For a large number of threatened bird species, no information on habitat requirements or population estimates are available. We show for one of the least-studied African birds, the Oberländers Ground-Thrush Zoothera oberlaenderi, how a first assessment of its habitat preferences and population size can be done if a short-term census is combined with a GIS-based species–habitat analysis. Between 9 February and 14 March 2008, we made intensive field surveys, using point counts and mist-netting in Semliki and Bwindi Impenetrable National Parks (BINP), two forests in Uganda from which there are previous records. While the species was not recorded in Semliki, eight were heard singing in BINP. We made the first analysis of this species’ habitat preferences by analysing all records of the species with variables extracted from GIS layers for the BINP. It preferred dense forest types, close to rivers and at elevations of 1 500–1 935 m. Using detailed habitat information we calculated 30 km2 of suitable habitat (out of the 331 km2 in BINP), which could hold an estimated minimum of 36–45 males. Because there is on-going forest degradation and deforestation within its potential distributional range in Uganda and the Democratic Republic of the Congo, and because the population in Uganda appears so small, there is a need to reconsider the IUCN Red List category of the Oberländers Ground-Thrush, which is currently Near Threatened.