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A study of the birds in central Bangkok (Thailand) in order to implement the basis of a long term monitoring

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par Camille Calicis
Université de Gembloux Agro Bio-Tech - Master Bioingenieur en gestion des forêts et des espaces naturels 2014
  

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VI.3.1. Limits regarding the study scope

Due to all of the constraints affecting our green patches sampling, the patches selected show trends only regarding public areas within the most urbanized part of Bangkok. Other green patches alike zoos, vacant lands, privates gardens or street trees haven't been taken into account although they can be considered as well as green patches and they include avifauna potential habitat. It is therefore important to ask ourselves the question of the chosen patches representativeness as they represent only a part of the green patches within the study area. Furthermore, as the field work depended on existing structures, the patches didn't range in area and land cover types and the representativeness of the patches panel can also be questioned.

VI.3.2. Limits concerning the bird data collected

A second important fact concerning bird counting is the difficulty of getting relevant abundance data. Indeed, it has never been difficult for an ornithologist to create a list of the bird species recorded. However, calculating species abundance is difficult considering such a mobile animal. Their mobility could lead us to believe that they could be everywhere although this is not the case.

It is true that birds are easily seen compared with other taxa but while counting multi bird species, many studies tend (us also) to assume them as similar. However, identifying the proximal factor of the urban bird diversity is relatively difficult as well as studying urbanizations gradients and biological response because they are far from being linear (MACDONNELL and HAHS, 2008). Indeed, many parameters affect the bird species differently according to one species eco-ethology: detectability, response to the environment changes, adaptation to human disturbances...It is therefore a limit to assume the anthropic effect or the habitats as equal in the overall patches while those factors have variable influences for each species. Statistical models for individual species would be best understood from the perspective of each species' natural history and habitat preferences but as we focused on the overall bird distribution and because the number of species was important, we chose not to proceed in this way (PEARSON, 1993).

Nevertheless, as the study was made in order to implement the basis for long-term monitoring, the data obtained will be compared to future data collected in a similar way. Therefore, while forgetting the bias brought by another observer, the abundance scores specified will allow future surveys to detect large scale changes in the abundance of individual species.

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Concerning the identification process, the fact that the field work was a first ornithological survey experience and, in a foreign country, and despite the great motivation put into the bird visual and sound identification, a professional birdwatcher would surely have seen more birds. Hence, the species identifications we made were accurate concerning the abundant species while the multiplication of visual encounters allowed us to be sure of the species recognition. On the other hand, non-abundant less detectable species can lead to identification mistakes.

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