A Rocha Portugal Observatory Report 2009-2010

24 A Rocha Portugal Observatory Report 2009-2010
Heleno (2004). The length of time spent at each site was equal for each visit and across all the years as also
prescribed in Hayden & Heleno’s methodology (2004; 2005).
The number of breeding pairs was estimated by counting the number of territories which were apparently
being defended. An apparently held territory (AHT) was counted if a bird was sitting on a nest, the presence
of chicks, more than three occurrences of territorial behaviour at the same location across different dates,
or two occurrences of territorial behaviour with supporting non territorial behaviour (Hayden & Heleno,
2005).
Wader counts were conducted every fortnight on the Ria de Alvor estuary at high tide. These surveys cover
both the western marsh and western marsh salinas. These counts have been carried out from 1999 to 2010
by staff and volunteers at A Rocha. The maximum count utilised within this report is taken from surveys
carried out in April, May or June to coincide with the Kentish plover breeding period.
Results
The number of apparently held territories declined throughout the period from 53 in 2004, 43 in 2005 and
finally 30 in 2010. Similarly the number of birds seen sitting and the number of juveniles also declined. The
number of adult individuals shows greater variation from 344 in 2004 to 84 in 2005 (Figure 1). The 2010
figure (178 adult individuals) was between the numbers found in the two previous studies.
Figure 1 The total numbers across the last five visits of individuals (adults), juveniles, apparently held
territories and sitting birds. The last five visits are used so that all the years are comparable.
There is a significant difference in number of individual Kentish Plover over the years between the different
sites studied (Figure 2). In all four measures (number of individuals, sitting birds, juveniles and AHTs) the
Western Marsh showed greater abundance than the other sites, however it also showed the greatest
decrease from 2004 to 2010. The Western Marsh Salinas have generally shown the least decline over this
period, and actually showed an increase or the same result in three of the measures.
In 2010 the number of sitting birds in each site correlated significantly with the number of AHTs
(Spearman’s rank, rs= 1.6, d.f=3, p