Competition and Defence
The number of falcon pairs attempting to breed varied from one year to another. The variable size of a breeding population can produce a competition among pairs, especially where they faced with a shortage of suitable. In fact, nesting sites distances amo
- PDF / 556,959 Bytes
- 15 Pages / 439.37 x 666.142 pts Page_size
- 51 Downloads / 197 Views
Competition and Defence
3.1 Introduction The number of falcon pairs attempting to breed varied from one year to another (Cavé 1968; Wiklund 2001). This variation is due mainly to changes (1) in food supplies and, following Ricker’s equation, (2) in the number of individuals in the previous generation (Ricker 1954; Cavé 1968; Wiklund 2001). Of course, local weather conditions such as rainfalls and temperatures affect the density of breeding falcons but indirectly through prey abundances (Cavé 1968). In addition, the size of a breeding population at the start of the reproduction can produce a competition among pairs, especially where they faced with a shortage of suitable nesting sites (Cavé 1968; Wiklund and Village 1992; Rodríguez et al. 2007). Finally, distances among nests can vary in relation to the exploitation of favourable food patches (Cavé 1968). Abundances, availability, and spatial arrangements of food supplies produce an instantaneous plastic response of falcons supporting crucial decisions such as the choice of their breeding territories (Hanski et al. 1991; Wiklund and Larsson 1994). Overall when food supplies increase, falcons reduced their territory size, and, as consequence, there is an increase in the density of breeders and vice versa (Village 1989; Wiklund 2001). In favourable food years, the area suitable for breeding increases, and regularly used areas improve their quality (Wiklund 2001). Thus, food drives not only breeding densities but also the distribution of breeders (Court 1986; Wiklund 2001).
© Springer Nature Switzerland AG 2020 G. Leonardi, Behavioural Ecology of Western Palearctic Falcons, https://doi.org/10.1007/978-3-030-60541-4_3
95
96
3 Competition and Defence
3.2 Abundance and Population Dynamics On a global scale, geographical and climatical variables define the overall trend in the species’ distribution during both breeding and wintering seasons (Booms et al. 2009; Nantón 2011; Zellweger-Fischer et al. 2011; Sarà 2014; Sutton and Puschendorf 2020). On the other hand, local density and distribution of breeders depend on food supply that also affected overwinter survival of individuals (mainly males; Reichholf 1977; Newton 1988; Village 1989; Wiklund 2001). A falcon population can grow through an increase in breeding density and/or an expansion of breeding distribution (i.e. using new or secondary nest sites; Village 1983; Crick and Ratcliffe 1995). This assumption presupposes that abundance depends on peculiar habitat and nest-site requirements of each species (Newton 1988; Nantón 2011). For example, a long-term historical analysis demonstrates that more than 60% of nest sites used by gyrfalcons are the same in the last two centuries (Johansen and Østlyngen 2011). Similarly, peregrine falcons historical occupancy can be traced back for over 100 or even 200 years up to 350 years (Ferguson-Lees 1957). These ‘traditional’ sites are re-occupied also after very long time such as after the pesticide crisis (Andreasen 2008). However in several regions, the distribution of
Data Loading...
