acta oecologica 34 (2008) 1–8 available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/actoec Original article Site fidelity in the Canary Islands stonechat Saxicola dacotiae in relation to spatial and temporal patterns of habitat suitability Juan Carlos Illeraa,*, Mario Dı´azb aIsland Ecology and Evolutionary Research Group, IPNA, CSIC, 38206 La Laguna, Tenerife, Canary Islands, Spain bInstituto de Recursos Naturales, Centro de Ciencias Medioambientales, CSIC, C/ Serrano 115 bis, E-28006 Madrid, Spain article info abstract Article history: We investigate the degree of territory faithfulness of the Canary Islands stonechat Saxicola Published online 13 February 2008 dacotiae, an endemic bird species of the semi-arid island of Fuerteventura (Canary Islands, Spain), and the spatial and temporal variability of habitat traits related to its breeding suc- Keywords: cess over its whole distribution range. Between 1998 and 2003 we monitored the spatial lo- Arid ecology cation of individually marked birds to determine whether they were site faithful. We also Canary Islands stonechat analysed the spatial and temporal variability of the abiotic (rainfall) and biotic (food avail- Fuerteventura ability, abundance of avian predators and competitors, and nest predation) factors that Habitat quality may influence breeding success in this species. Canary Islands stonechats were strongly Site faithfulness site faithful. Out of 106 individuals, 86 (81.0%) were re-sighted during the whole study pe- Saxicola dacotiae riod, and most re-sightings (76; 88.4%) were in the territory where they were initially Semiarid habitat caught. Dispersal events were rare both within (1%) and between (6%) consecutive years, Spatial homogeneity and detectability of colour-ringed birds was as high as 87%. No significant spatial variation of abiotic and biotic factors affecting success was found at a range of spatial scales. Low spatial variance in the habitat characteristics determining reproductive success could have favoured site fidelity in this species, as costs associated with changing site would not be compensated for by significant increases in survival or breeding prospects in new territories. Strict protection of the areas already occupied by this ‘‘Endangered’’ narrow range endemic bird would be the most effective way of preserving it, due to its strict hab- itat and microhabitat requirements and its strong site fidelity. ª 2008 Elsevier Masson SAS. All rights reserved. 1. Introduction ecological factors such as morphological design, abundance and quality of food, availability of breeding sites or presence Mobile individuals must decide where to live. The frequency of competitors, predators and parasites (Cody, 1985; Stephens with which this decision has to be made can vary from once and Krebs, 1986; Wiens, 1989; Newton, 1998). only to repeatedly over the lifetime of an individual. The deci- Birds are highly mobile organisms. Nevertheless, individ- sion of where to live will be constrained by evolutionary or uals that show site fidelity by returning to their breeding or * Corresponding author. Tel.: þ34 922 260190x277; fax: þ34 922 260135. E-mail address: [email protected] (J.C. Illera). 1146-609X/$ – see front matter ª 2008 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.actao.2008.01.003 2 acta oecologica 34 (2008) 1–8 wintering territories year after year have been recorded in many species of migratory birds (e.g. Cuadrado et al., 1995; 2. Material and methods Latta and Faaborg, 2001; Pyle et al., 2001; Hoover, 2003). Site fi- delity is predicted to be maintained by various benefits includ- 2.1. Species and study area ing pairing with a familiar partner (Schieck and Hannon, 1989), or because familiarity with an area can improve the The Canary Islands stonechat is a small passerine endemic to ability of individuals to escape predators, to forage success- the Fuerteventura Island. It breeds across the entire island fully, or to identify better nesting sites (Greenwood and where suitable habitat occurs, favouring ravines and slopes Harvey, 1982; Shields, 1984; Stamps, 1995; Schjørring et al., covered by boulders and shrubs and avoiding sandy areas 2000). Furthermore, site faithful individuals may benefit and recent lava flows. Habitat and microhabitat selection de- from the presence of familiar neighbours, as the costs of terri- pend on food (arthropod) availability and presence of perches torial defence (time spent singing or fighting) has been shown and suitable nest sites (Illera, 2001). Canary Island stonechats to increase when neighbours change (Falls and McNicholl, are strictly sedentary. Individuals pair up and establish terri- 1979; Ydenberg et al., 1988; Eason and Hannon, 1994). tories and then defend them against conspecific intruders In spite of these advantages, if fitness benefits obtained on year round (Illera, 2004a). Territory shapes are irregular, and the current breeding site are low (i.e., low reproductive suc- sizes can vary among breeding seasons but rarely exceed an cess), then individuals are predicted to change breeding site area of 250 m in radius (around 20 ha; Illera, 2004a). The breed- in favour of sites where fitness prospects may be better. ing period extends from December to April (Illera and Dı´az, Many studies have found that low breeding success decreases 2006). In wet years, pairs breed over more extended periods site fidelity and that individuals tend to return to sites where and lay two clutches, whereas in dry years they breed only they have bred successfully (Beletsky and Orians, 1991; once or not at all. The number of fledglings is mostly deter- Switzer, 1997a; Blums et al., 2002; Hoover, 2003). The most ac- mined by nest predation and breeding effort (which is posi- cepted behavioural rule for site fidelity is that individuals tively related to rainfall; Illera and Dı´az, 2006). should choose to stay in their territories if the previous breed- The Canary Islands are a volcanic archipelago located in ing attempt was successful (‘‘win-stay’’) or to switch to a new the north-eastern Atlantic Ocean, 100 km west of mainland nest site if their reproductive success was low (‘‘lose-switch’’; Africa. It comprises seven main islands and several islets Switzer, 1993; Schmidt, 2001, 2004). that emerged during different eruptive episodes from the Mio- Apart from previous experience, the decision to stay or cene to the present (Carracedo and Day, 2002). Fuerteventura leave a site will be influenced by the costs associated with is the island closest to the mainland, the oldest (c. 22 million moving to, and settling into, unfamiliar territories (Switzer, years old; Carracedo and Day, 2002), and the second largest 2 1993; Jakob et al., 2001; Yoder et al., 2004), and on whether (1659.71 km ; Fig. 1). Its topography is mostly low and flat the benefits of moving compensate for these costs. Neverthe- (c. 200 m a.s.l.), with a maximum elevation of only 807 m. less, the costs and benefits of this trade-off in relation to envi- The climate is semi-arid. Rainfall (143 mm/year on average) is ronmental heterogeneity have, so far, rarely been explicitly strongly seasonal, with most rain falling during the autumn/ addressed (Switzer, 1997b). Most empirical studies on the winter months. Monthly rainfall records were obtained from site fidelity of birds have been carried out on migratory species four weather stations located close to the field sites (Fig. 1). with wide distribution ranges (references above). High spatial Mean monthly temperatures varied between 19 C in January variability in the quality of unoccupied territories is taken for and 21 C in August (Marzol-Jae´n, 1984). The vegetation is granted for these species, and such variance can compensate dominated by sparse and xerophytic shrubland (Rodrı´guez for moving and settling costs. However, this may not be the et al., 2000). case for sedentary species with narrow ranges. Strong site fi- delity may be maintained in these species if spatial variability 2.2. Ringing and monitoring of Canary Islands in habitat characteristics associated to fitness is low, even in stonechats the face of high temporal variability in breeding success and territory quality (Switzer, 1993). We ringed and monitored birds from December 1998 until We monitored the spatial location of individually marked March 2002 in 17 localities randomly distributed over the Canary Islands stonechats, Saxicola dacotiae, a bird species northern, central and southern parts of the island (Fig. 1). Birds endemic to the semi-arid island of Fuerteventura (Canary were caught with clap-nets placed below foraging perches us- Islands, Spain), from 1998 to 2003. Apart from documenting ing Tenebrio molitor larvae as bait. Each individual was ringed whether birds were faithful to their territories, the goal of with a unique combination of an aluminium ring (Spanish this study was to analyse the spatial and temporal variabil- Environmental Ministry) and two colour rings. Ringed birds ity of the abiotic (rainfall) and biotic (food availability, abun- were released at the point of capture which was located to dance of avian predators and competitors, and nest the nearest meter using a Global Positioning System. predation) factors that determine the among-year variability We monitored birds each month using observations made in breeding success of this species (Illera and Dı´az, 2006). along 1-km line transects and random visits made throughout Low spatial variability in these factors over the distribution the island. Transects were performed either in the morning area of the species is predicted to be associated with site (from 08:00 until 12:00) or during the afternoon (from 16:00 un- faithfulness, whereas high spatial variability would pre- til 19:00), avoiding rainy, very windy and cloudy days. We clude it if breeding success or habitat quality varies in chose the transect approach because it is a suitable method time (Switzer, 1993). for detecting birds in open landscapes such as those of acta oecologica 34 (2008) 1–8 3 30 km LANZAROTE LA PALMA 29ºN TENERIFE LA GOMERA FUERTEVENTURA 28ºN N GRAN EL HIERRO CANARIA 18ºW 17ºW 16ºW 15ºW 14ºW Fig.