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Información detallada del proyecto
22 Mayo 2012
Rapid assessment of bird diversity and abundance in riparian habitats in the Panama Canal Watershed: effects of land uses
Proyecto escrito por el Dr. Gregorio Magno Toral y revisado por la Dra. Sunshine A. Van Bael.
Abstract
The decline of forest bird populations with the increase of forest loss to agriculture and other human land uses in the American tropics has been documented by several long-term studies. However, different types of land uses hold profoundly different consequences for bird diversity.
Effective monitoring of species distributions and abundances is necessary in order to assess the relative importance of different sites, the effectiveness of management activities and population trends. In this regard, rapid assessments can generate high quality data sets to inform conservation policy for understudied and relatively unknown tropical areas.
The objective of my research project is to carry out a rapid assessment of the riparian avian community in the Panama Canal Watershed to explore how bird diversity and abundance are related to land uses including revegetation treatments. This research project fits into a broader study called the Agua Salud Project, which seeks to understand and quantify the diverse set of ecological, social, and economic services provided by tropical forests in the Panama Canal Watershed. The field site includes the Agua Salud Watershed and the headwaters of several adjacent rivers. One of the main objectives of the Agua Salud Project is to quantify the effect of different land uses on biodiversity values. However, there is a lack of information regarding bird species using riparian habitats. My research project seeks to fill this gap.
Research proposal
Introduction
Conservation requires effective monitoring of species distributions and abundances in order to assess the relative importance of different sites, the effectiveness of management activities and population trends (Mace and Baillie 2007; Marsh and Trenham 2008). In this regard, rapid assessments can generate high quality data sets to inform conservation policy for understudied and relatively unknown tropical areas (O'Dea et al. 2004).
An enormous global research effort has focused on understanding the dynamics of riparian zones (i.e., the biotic communities living on the shores of streams, rivers and lakes) (Naiman et al. 2000). Riparian areas are among the most important biosphere’s ecological systems for maintaining the vitality of the landscape and its rivers (Naiman and Décamps 1997). The decline of forest bird populations with the increase of forest loss to agriculture in the American tropics has been documented by several long-term studies (e.g. Sekercioglu et al. 2002; Sigel et al. 2006). However, different types of land uses hold profoundly different consequences for bird diversity (Van Bael et al. 2007). To reverse the effects of clearing of tropical rainforests, revegetation is advocated to assist in arresting declines in biodiversity (e.g. Goosem and Tucker 1995; Bennett et al. 2000); however there has been little research on the effects of revegetation on wildlife (Tucker 2000; Munro et al. 2007, Freeman et al. 2009). Southern Central America provides an ideal opportunity for assessing drivers of change in local species richness (Condit et al. 2002), especially in lowland tropical forests in central Panama, near the Panama Canal (Rompre et al. 2007).
The objective of our research project is to carry out a rapid assessment of the riparian avian community in one area of the Panama Canal Watershed to explore how bird diversity and abundance in rivers/streams are related to land uses including revegetation treatments. This assessment will serve as a starting point, with the idea of seeking further funding to expand to other parts of the Panama Canal Watershed.
This research project fits into a broader study called the Agua Salud Project (http://www.ctfs.si.edu/aguasalud/), which is directed by Dr. Jefferson S. Hall and seeks to understand and quantify the diverse set of ecological, social, and economic services provided by tropical forests in the Panama Canal Watershed. The field site includes the Agua Salud Watershed and the headwaters of several adjacent rivers. The region encompasses both protected mature forests and a wide variety of land uses including pasture, invasive grass (Saccharum spontaneum – canal grass) and three revegetation treatments following pasture: native-species plantation, native second growth, teak plantation, and a native species plantation following S. spontaneum.
One of the main objectives of the Agua Salud Project is to quantify the effect of different land uses on biodiversity values. Dr. Van Bael’s research team has already carried out bird surveys in the area focused on terrestrial habitats. However, there is a lack of information regarding bird species using riparian habitats. My research project seeks to fill this gap comparing bird diversity and abundance in the rivers/streams in Soberania National Park (natural habitat) versus Agua Salud Project sites.
Methodology
Bird surveys
In order to compare bird species richness and abundance in riparian habitats among the different land uses, we will sample birds using fixed-radius point counts (25 m radius) to record all visual signs of birds. The survey points will be located in the banks of the streams and/or rivers within each of the 14 transects that were already defined in a preliminary study carried out by the scientific staff of the Agua Salud Project. Hydrologists currently working in the Agua Salud Project will give advice on the appropriate locations of the survey points to make then comparable among different habitats. Within transects, survey points will be separated by at least 100 m to minimize the risk of counting the same individual twice. Ten minutes will be spent at each point, allowing for the identification of all birds present while minimizing the likelihood of double-counting individuals arriving or moving during the survey period (O'Dea et al. 2004).
There are two transects each in these habitats:
1) Old forest (Soberania National Park)
2) Secondary regenerating forest
3) Cattle Pasture
4) Invasive Canal Grass area
5) Live fences around Cattle Pastures (no riparian habitat here)
6) Native tree species reforestation plantations
7) Exotic tree species (teak) plantations
We will also use the MacKinnon lists (ML) technique (MacKinnon & Phillips, 1993) since it was originally developed for rapid assessment of avian species richness in tropical environments (Bibby et al. 2000; MacKinnon and Phillips, 1993). Authors have recommended the adoption of this straightforward technique for examining the impacts of habitat modification and habitat disturbance on bird communities in the tropics (Fjeldsa, 1999; Trainor, 2002). The ML samples are suggested to be independent of the amount of time needed to collect them, the spatial extent over which they are collected and observer experience of the focal avifauna (MacLeod et al. 2011). The ML method consists of listing all individuals encountered in chronological order of detection. This master list is then broken down into lists or samples of 10 species. Each list thus provides a sample of the species community at the study site. The ML method can then be used to derive abundance indices of individual species by calculating the proportion of samples in which each species occurs (Bibby et al. 2000; MacKinnon and Phillips 1993).
Using the Mackinnon list method in conjunction with point counts has been recommended, as this may provide robust rapid-survey data, including both an accurate assessment of species richness as well as compositional and relative abundance data that can be directly related to environmental variables (O'Dea et al. 2004).
Bird species recorded in the point counts will be also recorded in MacKinnon lists to ensure maximum sampling using the MacKinnon list methodology (O'Dea et al. 2004). As suggested by Herzog et al. (2002), birds encountered during, between, and after point counts will be recorded in MacKinnon lists, since these additional data can be used to ensure a more accurate assessment of the magnitude of species richness in an area. Descriptions will be taken of any bird not immediately identified but that was seen sufficiently well for identification. These individuals will be subsequently identified using standard reference works (MacLeod et al. 2011).
Environmental variables
The composition of riparian wildlife communities is influenced by stream size and habitat characteristics associated with forest successional stage (Naiman et al. 2000). Thus, to associate habitat features with bird counts, we will sample stream/river characteristics including vegetation. We will measure the width and depth of the stream/river. We will sample vegetation using slightly modified methods of James and Shugart (1970). We will collect data on the vegetation characteristics within the 25 m radius circle at each census point. We will estimate canopy cover and structure at 5 subpoints within the circle; the center and at approximately 12 m N, S, E and W of the center subpoint. To estimate canopy cover we will take readings with a hand-held concave densiometer at each of the 5 subpoints. To estimate canopy structure (depth), at each of the 5 subpoints we will record the height of the lowest and highest canopy vegetation immediately above the subpoint. The difference in the highest and lowest vegetation heights will be used to estimate canopy depth at the 5 subpoints within each circle (Van Bael et al. 2007)
Statistical analyses
Simple species accumulation curves will be generated and compared for data collected using survey points and ML for each habitat. A plateau in the species accumulation is defined here as the point where the rate of species accumulation over a 10-sample interval falls below 0.10 (O’Dea et al. 2004). According to Herzog et al. (2002) the Chao 2 (Chao, 1987) species richness estimator will also be calculated for these data:
SChao = Sobs + F21/ 2F2
where Sobs is the number of species observed, F 1 is the number of species with exactly one individual and F 2 is the number of species with exactly two individuals. Curves generated indicate whether sufficient sampling effort has been undertaken to capture the total species richness of the habitat in question. They also indicate whether differences exist in the expected total species richness of these habitats.
We will use multiple regression models (general linear models) to determine whether bird diversity was related to vegetation variables.
Expected results
This research project will be, to the best of our knowledge, the first study reporting information about the effect of different land uses on avian diversity and abundance in the riparian habitats of the Panama Canal Watershed. This information will help to choose whether to focus conservation actions to protect the populations of this group of species. Furthermore, since the Agua Salud Project is a long-term project, the results obtained will be useful as a first reference to be compared to the results of future surveys in the area.
References
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