Gnome Projector Slides

Issues to census birds 2. Difficulties in extrapolating results. The Peruvian Cortarrama the Illescas Peninsula as an example. Issues to census birds

Irma Franke

Figura 1. Cortarrama Peruana, Phytotoma raimondii

is important to know how many individuals of a species inhabiting the Peruvian territory or a certain region?

know the total size of the population of a species throughout the Peruvian territory or in a certain region is not an easy task and is important only for some species and in certain circumstances. It is more common to calculate the relative density of some species in a given area muestreal, allowing comparisons between areas and monitor changes over time.

Usually

it comes to knowing the total population of a particular region or management purposes to monitor changes that occur naturally or by human influences. Knowing the total population is especially important for species of restricted distribution and conservation purposes.

Difficulties in extrapolating density estimates obtained in areas muestreales?

The ideal method to determine the size of the population is the total counts. However, this method can be applied a small number of species. This difficulty has been to use methods that are to determine the relative density of an appropriate number of areas muestreales and extrapolate the relative density obtained from the total area occupied by the species.

There are several methods for calculating the relative density muestreales areas, which have their own difficulties each. But a very serious problem on which it is important to stress when it comes to estimating the total size of the population of a species is the size of the area which are to extrapolate the results, also called area of \u200b\u200boccupancy.

How to determine the actual area occupied by a species? One approach used is to consider the extension of the typical habitat of the species seem easy task especially if it is a bird with great specificity for a given habitat and extent of habitat can be estimated using aerial photographs for example.

As in most cases it is clear that many species occupy only part of the habitat that could potentially use their area of \u200b\u200boccupation, another possibility is frequently considered to estimate one or more areas known muestreales the percentage extension of habitat actually occupied by the species.

The Cortarrama Peruvian , Phytotoma raimondii, in Illescas Peninsula as an example.

An example of the problem can be illustrated in relation to the Peruvian Cortarrama , Phytotoma raimondii (Figure 1). This endangered bird endemic Peruvian exclusively inhabits the dry forests of northwestern Peru. Its known distribution in this environment is very punctual ( Flanagan et al. 2009), and their specific requirements in the dry forest are poorly known (Flanagan and More 2003, More 2002, Flanagan & Millen 2008). For very few known populations of the Cortarrama censuses have been made and fewer still defined the area they occupy.

A population of this species was found in the foothills Illescas in the department of Piura. Illescas Peninsula is one of Peru's largest part Sechura desert. Its surface is characterized by the presence of a natural depression that is about 20 m below sea level and the presence on its western edge of the Cerro Illescas, of 500 m elevation. Much of the surface of the peninsula is dry forest patches of varying length and condition. These patches of dry forest were sampled en.junio 2006 and February 2007 (Golder Associates Peru SA 2007). The samples included both occasions distributed patches of dry forest throughout the peninsula (Figure 2). In June 2006 there were 18 individuals in 11 points (Figure 3) and February 2007 there were 27 individuals in 5 points. The Cortarrama was absent from the rest of the patches. All patches where the bird was recorded were located in the foothills of the Cerro Illescas forming a belt on the basis of its eastern slope, with a concentration of greater density to the south of this area (Map 3).

Figure 2. Dry forest patches sampled in June 2006
Illescas

Figure 3 Peruvian Cortarrama distribution in Illescas in June 2006

Figure 4. Peruvian Cortarrama distribution in Illescas in June 2006 (red) and February 2007 (green)

The questions we ask are:

1. If it is determined using aerial photographs the total area of \u200b\u200bdry forest Illescas Peninsula and the extent of the area occupied by the Peruvian Cortarrama could obtain the percentage of dry forest in the area occupied by this bird. Would be valid to apply this proportion to other areas of dry forest?

2. If to correct this possible error in percentage of area occupied similar calculations to perform the test in other areas with similar samples and promediáramos the values \u200b\u200bobtained for the proportion of dry forest area occupied by the Cortarrama, we could apply this percentage averaged a total area of \u200b\u200bdry forest with a degree of certainty of approaching the actual area of \u200b\u200boccupation of this bird?

is clear that the distribution of Cortarrama Illescas Peninsula in the distribution is not random but due to some factor in the sector where that is currently unknown and is most probably related to local conditions habitat. Only More detailed studies on this species can clarify their specific habitat requirements.

3. If we obtain the relative density of the Cortarrama in the area it occupies in Illescas Peninsula and some of the few other areas where this species is known, would be valid to extrapolate this value or average value to the entire forest area existing dry?

The error in such extrapolations can be very thick and represent an overestimation or underestimation too large in area of \u200b\u200boccupancy and total population size of birds with small populations and so little known. References




Flanagan, JNM, Engblom, G., Franke, I. Valqui, T. & Angulo, F. 2009. Distribution of the Peruvian Plantcutter Phytotoma raimondii (Passeriformes: Cotingidae). Rev. peru. biol. 16 (2): 175-182

Flanagan, JNM, and Moore, A. 2003. Ecology and conservation of Peruvian Cortarrama (Phytotoma raimondii) in the sparse dry forest of northwestern Peru. In: Proceedings of First International Dry Forest (6-9 Nov. 2003). Universidad de Piura, Peru.

Flanagan, JNM, & B. Millen 2008. First records of nest and egg Phytotoma Peruvian Plantcutter raimondii, by OD Boggs. Bulletin of the British Ornithologists' Club, 128: 271.

Golder Associates Peru SA 2007. Environmental Impact Study, Bayóvar Phosphate Project, Piura, Peru. Prepared for Compania Minera SAC May Miski More

, A. 2002. 'Floristic Composition and Structure raimondii Phytotoma Habitat (Taczanowski, 1883). "Cortarrama Peruana" Dry Forest in Talara.'. Thesis for the degree of Biologist. School of Biology.