A Rocha Portugal Observatory Report 2009-2010

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26 A Rocha Portugal Observatory Report 2009-2010 Figure 3 Maximum number of Kentish Plovers recorded in the Alvor Estuary on fortnightly wader counts. The number is the highest observed number of Kentish Plovers on any given wader count in April, May or June. The linear regression line is plotted indicating a decline. Supporting data Before the current methodology was adopted in 2004 A Rocha carried out numerous surveys on Kentish Plover. From 1991 to 1999 surveys of Kentish Plover were carried out in six of the years with estimates of the number of breeding pairs ranging from 45 to over 200. However, almost every survey used a different methodology with different amounts of time spent in observation, therefore any comparisons with data gathered before 2004 must be made with caution. A Rocha has also conducted fortnightly wader counts over the study period and going back to 1999. Figure 3 reports the maximum number of Kentish Plover observed on any one wader count in the months of April, May or June. Results from months before or after these three have been excluded to avoid including the influx of individuals stopping in the estuary while on migration. Figure 3 indicates that wader counts show a slight decline in the number of individual Kentish Plovers seen during the breeding season (linear regression: y=-0.395x + 34.65), from 1999 to 2010. The highest numbers range from 20 to 48, indicating a great variation in the number of individuals; some years have double the number counted in other years , with the linear regression having a low r-squared value (r 2 =0.07, d.f.=10, p=0.67).
Discussion A Rocha Portugal Observatory Report 2009-2010 27 Salinas The importance of salinas has changed through the period this study encompasses. For all observed sites 2010 had lower numbers of individuals and fewer sitting birds, except for the Western Marsh Salinas which showed slight increases for both. Importantly, due to changes in land access, not all of the salt pans could be accessed in 2010, which means the latest figure may be a slight underestimate compared with previous years. The other salt pans, at Odiaxere, showed similar declines to all the other sites. This increase in Kentish Plover on the Western Marsh Salinas is potentially made up of individuals from Western Marsh itself. In 2010 the sluice gate controlling the water levels in the Western Marsh was open allowing water to flow in and out with changes in the tide level of the neighbouring estuary. The result of the sluice gate being open is that high tides caused water levels to be higher in the marsh than in previous year. This may have caused Kentish Plover to nest on the neighbouring Salinas. A previous study by Rufino, et al., (1984) looking at the use of salinas by waders at Ria Formosa, also in southern Portugal, found that over 89% of Kentish Plover roosted in the salinas, and when feeding 61% were in the salinas compared to 39% in the Ria. This study therefore complements their findings in emphasising the importance of salinas for waders, and extends their importance for breeding in addition to roosting and feeding. Sand dunes A possible reason for the dunes having very low numbers of Kentish Plover may be due to the extensive disturbance that they have suffered. During the end of 2009 and up until April 2010 dredging was carried out in the Alvor Estuary which resulted in the dredged sand being placed on the Meia Praia and Alvor dunes before being transported to beaches. This obviously caused major disturbance and change to the topography and vegetation of the dunes. In the summer the beaches neighbouring the dunes are very popular with tourists, with people regularly walking through the dunes and walking their dogs which are most often not on a lead. This obviously causes major disturbance for the Kentish Plover. In 2005 signboards were used to try to reduce the number of people walking through the dunes and encourage people to have dogs on leads (Sousa, et.al, 2007). Calculating territories The measure AHT was found to positively correlate with the number of sitting birds in 2010. When combining results from all years the number of AHTs correlated with all the measures (number of individuals, sitting birds and juveniles). This suggests that AHT successfully incorporates the results as the number of territories would be expected to increase with individuals, sitting birds and juveniles. It is not necessarily surprising that the correlations are not always significant for a single year due to their only being five values which often results in ties in the ranking making p-values impossible to predict accurately. Additionally, calculating the number of territories can sometimes be difficult given that many of the birds are seen very close together over numerous visits. This can make it hard to determine how many territories have been seen. Therefore the decline in the number of AHTs must be interpreted cautiously. However, it is promising that 2010 had a much higher number of individuals counted than 2005. The results suggest that the Kentish Plover population in the Alvor Estuary is very variable in the number of individuals, although this variation is not seen in the number of juveniles or sitting birds, which probably
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