20 Jan 2017
Kentish Plover (Charadrius alexandrinus) in north-western Iberia before and after the Prestige oil spill

BRANTA — María Vidal Malde

Kentish Plover (Charadrius alexandrinus) in north-western Iberia before and after the Prestige oil spill

Institution: University of Santiago de Compostela, Spain

Supervisors: Jesús Domínguez Conde

Details: PhD, 2014


Subject Keywords:waders, pollution, oil-spill, Prestige, recovery
Species Keywords: Kentish Plover, Charadrius alexandrinus


Kentish Plover (Charadrius alexandrinus) is the only wader nesting on the Atlantic coast beaches of N Iberia. In the stretch of the Spanish coastline between Portugal and France, the breeding population is very small and located exclusively in Galicia. The Galician population, consists mostly of resident birds, which select sparsely-vegetated beaches for foraging, roosting, nesting and rearing young. The lifestyle of this population makes them especially vulnerable to oil-spill pollution.

Until the 1990s, there were major gaps in knowledge about the reproductive biology, conservation status, distribution and population trend of Kentish Plovers in NW Iberia, as well as the implications for them of oil spills. So, the main goal of this work focused on the study and evaluation of these parameters in relation to the occurrence of a major oil spill, like the produced one by the break-up and sinking of the tanker Prestige off the Galician coast in 2002.

Essential to the proper evaluation and assessment of recovery from the impact of a spill event on a population, species or community, is continuous up-dating of knowledge over a long period of time, including years before the spill. Thus, this thesis covers the results of the study and monitoring of the Galician population of Kentish Plovers from 1996 to the present.

The role of researchers

In Chapter 1, we describe an experimental study to evaluate the effect of researchers on Kentish Plover nesting success on the main breeding beach in Galicia. The results showed no negative effects of our presence in the vicinity of the nest. Daily survival rate during the incubation period was higher in disturbed nests, which could be interpreted as a positive effect of monitoring activity explained by the high sensitivity of nest predators and their avoidance of research activities. However, the high rate of nest losses in both visited and non-visited nests, the large numbers of humans on the beach and the difficulty of identifying causes of mortality, could mask the effect of researchers on Kentish Plover nest success.

Status and population trend

In Chapter 3 we assess the Galician Kentish Plover population trend from 1988, with the aim to elucidate potential Prestige effects on abundance and distribution. Data showed a population decline up to 2004 followed by a moderate increase until 2010. These changes were substantial both with regard to population size and habitat use, with an increase in the number of birds and breeding locations and changes in distribution along the entire Galician Coast.

The redistribution of plovers along the Galician coast seemed to be related to the level of exposure of the beaches to the Prestige pollution, so birds from heavily impacted areas were displaced to better breeding habitats. This impact persists to the present time in that the distribution of the birds has not recovered to pre-spill conditions.

Increasing bird numbers from 2005 agree with results observed in the analysis of the genetic structure of Kentish Plovers in Iberian Peninsula (Chapter 2). So, in view of doubts around the Spanish and Portuguese population trends, our results do not support the recent decline hypothesis because there is evidence of population expansion for Atlantic coast population. At the regional level, population growth was attributed to the combination of three main factors: successful management strategies undertaken at many of the Galician Kentish Plover breeding beaches after the Prestige oil spill, changes occurring in the spatial distribution of the breeding pairs and immigration of birds from other sites.

Re-sighting of marked birds confirmed the dispersal of individuals between the Galician and Portuguese Coasts. This dispersal seems responsible for the high gene-flow observed across Iberia (Chapter 2). However, taking into account the extremely low hatching success and high site-fidelity of the Galician population, dispersal would be asymmetric. We hypothesise that the Kentish Plover population along the Galician coast represents a sink that would decline in the absence of immigration from other population(s). Moreover, this sink hypothesis could explain the extinction of the Cantabrian population that may have depended on the immigration of plovers from Galician beaches. This Cantabrian population disappeared in the late 1970s when the Galician population was estimated at less than 47 pairs.

The Prestige oil-spill, first signs

Oiled Kentish Plover adults were detected a few days after the oil-spill reached the coast. In Chapter 4 we evaluate the level of the oiling of plumage, taking account of the characteristics of the nesting beaches and the progress of the season. The affected parts were primarily the abdomen and to a lesser extent, the breast.

Heavily oiled birds were observed on non-estuarine beaches, which are the most exposed to the arrival of the fuel. However, the distance from the beach to the initial oil spill did not explain the distribution of affected adults. Oiled birds were highly dispersed throughout the Galician coast, probably due to the great extent of the spill and the strategy for managing the Prestige which meant that it sailed a considerable distance between the initial accident, when it started leaking oil, and the time it sank.

As the breeding season advanced, there was a decrease in the amount of oiling on plumage of the plovers, probably as a result of the partial moult of contour feathers as well as the cleaning of oil due to the action of water and preening. Nevertheless, there was slight inter-monthly variation in the degree of oiling, suggesting that oil persisted on the substrate.

Therefore the oil spill did not apparently cause direct mortality to plovers but plumage oiling of breeding adults indicated that the eggs might be contaminated.

The Prestige oil spill, sublethal effects

In Chapter 5 we analyze the levels of polycyclic aromatic hydrocarbons (PAHs) in Kentish Plover eggs from NW Iberia, and try to elucidate any spatial or temporal patterns. Results suggest that the occurrence of PAHs in eggs is extensive, despite the high metabolic capacity of the birds. There were no spatial differences in the total PAH levels, probably due to the high dispersal of fuel related with the strategy used for managing the Prestige from the initial accident to the time of its sinking. However, PAH levels showed significant trends with year, with a decline in the first years and a substantial increase in 2007. In 2007, an important change was observed, not only in total PAH concentration, but also in the pattern of PAH accumulation. High molecular weight PAHs, indicative of a pyrogenic source of contamination, showed a substantial increase. We related this fact with the extensive forest fires that occurred in Galicia during summer 2006, with high incidence in coastal areas.

Our study provides information on the background levels of PAHs in coastal birds after a large oil spill and quantitatively shows the importance of other contamination sources. Therefore other sources of pollution related to major wildfires and other natural sources of PAHs in the coastal environment can maintain high levels of these pollutants, which may have consequences for the fitness of plovers including adult survival.

In Chapter 6 we analyzed long-term data (1996-2011) on NW Iberian Kentish Plover breeding success, egg structure, female condition and breeding effort to ascertain the existence of sublethal effects of Prestige oil on reproductive performance and length of time of reproductive disruption.

Combined pre- and post-spill data showed that plover egg structure and breeding performance changed over time. Eggshell thickness and egg volume showed variations after the spill event, we found females in poor condition and recorded nest abandonment. Data showed a change in the pattern of intraclutch egg-size with a trend towards homogenization in the years after the spill.

In our population, breeding success is restricted by the high rate of predation, so we consider both hatching success and fledging success to be invalid parameters for evaluating the effects of oil exposure. Our results showed no pre- post-Prestige differences in hatching success and showed a high fledging success in the years following the spill event. The latter observation can be easily explained by the wardening efforts of nests and chicks made from 2003 to 2006 at the main breeding beaches. In contrast, egg fertility constitutes a valuable parameter that is highly related to the spill event, as oil can be responsible for embryo mortality. We found differences between periods, with lower fertility just after the oil spill. However, the low hatching success could be underestimated because a high percentage of nests are depredated before this can be measured. Lastly, nest desertion occurred at low levels only in the post-Prestige periods. Thus, we hypothesize that desertion was related to poor female condition, without precluding the influence of other factors, such as disturbance, which, in many cases, could interact with poor body condition to influence a bird’s decision to desert a nest.

We show that oil spill contamination has long-term complex consequences that may not be evident in terms of productivity in populations under high levels of early predation and may even lead to misleading interpretations. We encourage greater efforts to perform long-term assessments of the environmental impact of contamination episodes with an emphasis on species under conservation management protocols.

Published Papers

Vidal, M. & Domínguez, J. Did the Prestige oil spill compromise bird reproductive performance? Evidences from long-term data on the Kentish Plover (Charadrius alexandrinus) in NW Iberian Peninsula. Biological Conservation, in press.

Vidal, M., Hernández, M., Luis, A. & Domínguez, J. 2014. Lack of genetic structure in Kentish Plover (Charadrius alexandrinus) from the Iberian coast. What’s wrong with the endangered northwestern population? Bird Conservation International doi:10.1017/S0959270914000239.

Vidal, M. & Domínguez, J. 2013. Long-term population trend of breeding Kentish Plovers (Charadrius alexandrinus) in Northwestern Spain affected by a major oil spill. Bird Conservation International, 2: 386-397.

Vidal, M. & Domínguez, J. 2011. Spatial and temporal patterns of polycyclic aromatic hydrocarbons (PAHs) in eggs of a coastal bird from northwestern Iberia after a major oil spill. Science of the Total Environment, 409: 2668-2673.

Domínguez, J. & Vidal, M. 2009. Factors affecting plumage oiling levels in a Kentish Plover Charadrius alexandrinus population after a major oil spill. Acta Ornithologica, 44: 119-126.

Domínguez, J. & Vidal, M. 2003. Influencia del investigador en el éxito reproductivo del Chorlitejo patinegro Charadrius alexandrinus. Ardeola, 50: 15-19.

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