EN LA ZONA RURAL EXISTEN 10 PUESTOS DE SALUD ATENDIDOS

These analyses demonstrate that life-history traits, migration, phenology and resource use are associated with long-term population trends in UK passerines. Resource use, both habitat and diet, together with average 1st clutch laying period were strong predictors of population trends, suggesting that species able to utilise a wide range of resources and alter their phenology may be better buffered against environmental change, particularly in seasonal habitats (Both et al., 2010). Phenology and phenological flexibility was particularly important for migrants. Resident species are exposed to local climate conditions throughout the year, while long-distance migrants encounter conditions in their breeding range only after returning from over-wintering grounds. Thus the former have more, as well as better, cues to match their phenology to the changing environment (Végvári et al., 2009), which is supported by earlier laying dates in resident and partial migrants species (Jenni & Kéry, 2003; Rubolini et al. 2007).

The potential for migrant species to change breeding periods will be influenced by their ability to shift their migration timing appropriately. In most long-distant migrants, the spring arrival date is dictated by an endogenous rhythm based, in most cases, on changes in photoperiod (Dawson, 2008) though it has been suggested that climatic conditions on their journey to the breeding grounds may also impact species’ ability to adjust their phenology (Moussus et al., 2010). The fact that mean arrival date was the most important contributor to the best-fitted model for migrant species suggests that this timing is critical. However, long- distance migrants will have fewer relevant environmental cues than resident or short-distant migrant species (Møller et al., 2008). Thus, phenological responses through changes in laying dates will be greatly constrained by the onset of their spring migration and ultimately arrival date (Lehikoinen et al., 2004). However, it seems that even with these intrinsic limitations, migrants are still able to modify their breeding phenology to somehow buffer for the limited

54 breeding period, as migrants with longer laying periods and advanced arrival dates were less likely to have declining populations.

The positive association between longer reproductive periods and population trends complement those of Møller et al. (2008, 2010), Végvári et al. (2009) and Van Turnhout et al. (2010) who demonstrated that advanced laying date allows species to respond better to climatic change (particularly warming of spring temperatures). They found that long-distance migrants advance spring migration-date the least and that species laying larger clutches showed the greatest advance in the timing of spring migration. A longer laying period may allow re-laying in the event of brood failure or allow for an extra clutch under good conditions. Previous studies have highlighted complex interactions between phenological and life-history traits (Jenni & Kéry, 2003; Rubolini et al., 2007; Moussus et al., 2010). Species which can shift their phenology to match optimal food availability will be more likely to invest their efforts into producing one single, larger brood. In contrast, species unable to track changes in their environment may show phenological flexibility, but may try to compensate by having multiple clutches (Crick et al., 1993; Visser et al., 2003). However, in both cases the ability of species to respond appropriately may be restricted by an intrinsic limitation on clutch size increases (Winkler et al., 2002). As a final point, it has also been suggested (Visser, 2008) that species will be selected for adaptability to changes in photoperiod that may allow migrant species to reduce their migration distances and therefore winter in areas closer to their breeding grounds where they could better assess changes in environmental conditions there, and ultimately change the timing of their phenological events to allow them to respond accordingly.

Besides the key role of phenological flexibility buffering against declines, we also confirmed that specialized habitat and diet requirements may render species more vulnerable to declines (Both et al., 2004; Jiguet et al., 2007, 2009). Of all the traits we evaluated, both habitat preference and diet type showed the strongest association with population trends. In terms of habitat

55 characteristics, wetland species generally showed stable or increasing population trends which may be associated with increased protection from disturbance and the creation of wetland reserves as a result of both British and European legislation (Ramsar Convention Secretariat, 2006). Generalist species and upland species appear to fare better than farmland, woodland or urban species. Previous studies have suggested that agricultural intensification, loss of hedgerows, increasing use of chemical products (fertilizers and pesticides) and changes in crop and ploughing systems have negative impacts on survival and fitness of farmland species during the wintering period, influencing species pre-breeding conditions (Chamberlain et al., 2000; Gregory et al., 2005; Wilson et al., 2009). Though the food resources may be more stable and readily available in agricultural habitats, particularly with the establishment of environmental stewardship schemes, the negative impacts of agricultural intensification may outweigh the positive effects of these new management measures (i.e. the introduction of wild bird seed mixture), particularly in the case of resident species (Natural England, 2008). The fact that farmland species are more vulnerable may indicate that their habitat quality is decreasing globally through fragmentation and land use change (Devictor et al., 2008). Population declines in woodland species are related to both woodland maturity and reduction in active management (Amar et al., 2006) and climatic changes such as changes in winter temperature (Leech & Crick, 2007). In addition, since most of the woodland species in our study are specialist or invertebrate/insect eating species (11 out of 14) and migrant (8 out of 14), their decreasing population trends may also be explained by the increased mismatch between key reproductive period and the peak of food supply (Leech & Crick, 2007), particularly for migratory species. As explained above, threats to wild birds and biodiversity are currently monitored using population changes in indicator species from different breeding habitats (cf Gregory et al. 2009). Our finding that migration behaviour, habitat use and phenological flexibility have interactive effects on the ability of species to adapt to environmental change suggests that impacts on biodiversity may be better monitored using separate indicators for migrants and resident species.

56 It was predicted that additional life-history traits would be associated with species population trends. As indicated, species that reproduce more slowly may be expected to take longer to adapt to environmental changes, and thus be more likely to decline (Sandvik & Erisktad, 2008). Resident and partial migrant species had larger productivity than migrant species, which may indicate trade- offs between migration and reproduction. Specific-species traits may result in complex and potentially opposing responses to environmental conditions across the annual cycle which will need to be fully understood in order to be able to determine their ultimate effect on population trends (Jenni & Kéry, 2003).

Previous studies have linked broad features of range structure or resource use to inter-specific variation in ecological responses to environmental change (Møller et al., 2008, 2010; Végvári et al., 2009; Van Turnhout et al., 2010). These results not only confirm this but also highlight the importance of phenological characteristics and their interaction with other species traits (Moussus et al., 2010). These results also underscore the need for a multifaceted approach to understanding the mechanisms governing the differential impacts of environmental changes on species and show the relevance of interactions between phenology, habitat and resource-use characteristics when developing indicators.

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Chapter 3 : Environmental drivers of current avian community