Investigating patterns and processes of demographic variation: environmental correlates of pre‐breeding survival in red‐billed choughs Pyrrhocorax pyrrhocorax

Abstract

Summary 1.Quantifying the pattern of temporal and spatial variation in demography, and identifying the factors that cause this variation, are essential steps towards understanding the structure and dynamics of any population. 2. One critical but understudied demographic rate is pre-breeding survival. We used long-term colour-ringing data to quantify temporal (among-year) and spatial (among-nest site) variation in pre-breeding survival in red-billed choughs ( Pyrrhocorax pyrrhocorax ) inhabiting Islay, Scotland, and identified environmental correlates of this variation. 3. Random-effects capture-mark-recapture models demonstrated substantial temporal and spatial process variance in first-year survival; survival from fledging to age 1 year varied markedly among choughs fledged in different years and fledged from different nest sites. Spatial variance exceeded temporal variance across choughs fledged from well-studied nest sites. 4. The best-supported models of temporal variation suggested that first-year survival was higher in years following high tipulid larvae abundance and when weather conditions favoured increased invertebrate productivity and/or availability to foraging choughs. These variables explained up to 80% of estimated temporal process variance. 5. The best-supported models of spatial variation suggested that first-year survival was higher in choughs fledged from nest sites that were further from exposed coasts and closer to flocking areas, and surrounded by better habitat and higher chough density. These variables explained up to 40% of estimated spatial process variance. 6. Importantly, spatio-temporal models indicated interactive effects of weather, tipulid abundance, local habitat and local chough density on first-year survival, suggesting that detrimental effects of poor weather and low tipulid abundance may be reduced in choughs fledged from nest sites surrounded by better foraging habitat and lower chough density. 7. These analyses demonstrate substantial temporal and small-scale spatial variation in pre-breeding survival, a key demographic rate, and indicate that this variation may reflect interactive effects of weather, prey abundance, habitat and geography. These patterns illustrate the value of holistic models of demographic variation, and indicate environmental factors that may limit the growth rate of Islay's protected chough population.

Pronounced genetic structure and low genetic diversity in European red-billed chough (Pyrrhocorax pyrrhocorax) populations

“…Only six ringed individuals have been observed to disperse between Islay and Colonsay in over twenty years (although Colonsay was probably colonised from Islay in the late 1960s, Reid et al 2003Reid et al , 2008. Nevertheless, field observations show that choughs do occasionally disperse over long distances.…”

“…This work has identified intrinsic and extrinsic constraints on population growth rate (e.g. Blanco et al 1998a;Kerbiriou et al 2006;Reid et al 2004Reid et al , 2006Reid et al , 2008, and highlighted the key role of human impacts in the chough's decline, involving historic persecution (Monaghan 1988;Carter et al 2003), contemporary tourism pressure (Kerbiriou et al 2009) and agricultural land-use change (Blanco et al 1998b;Whitehead et al 2005;Kerbiriou et al 2006).…”

“…Colour-ring resightings also indicate that choughs in northwestern Europe are typically sedentary and philopatric as long-distance dispersal between populations is very rarely observed (Carter et al 2003;Reid et al 2003Reid et al , 2008Moore 2008). Nevertheless, occasional long-distance movements are observed, most notably between North Wales and the Isle of Man during 1997Man during -2004Moore 2006Moore , 2008.…”

Using diet to assess the sensitivity of northern and upland birds to climate change

“…The fact that this relationship remained significant despite these caveats, and the lack of accounting for other processes known to affect upland birds (Pearce-Higgins et al 2009a), suggests that it is worthy of further investigation. The negative correlation between ring ouzel population change and summer temperature (Beale et al 2006), and limiting effects of tipulid abundance on the survival of first-year chough Pyrrhocora pyrrhocorax, another tipulid specialist, supports this contention (Reid et al 2008). Detailed work replicating the approach of Pearce-Higgins et al (2010) on a wider range of species -particularly, dunlin Calidris alpina, whimbrel, ring ouzel and snow bunting, which are all declining -should therefore be conducted to test whether this correlation is causative.…”

Early development, recruitment and life history trajectory in long-lived birds

“…Similarly, Cam et al (2003) found evidence of long-term consequences of the length of the rearing period on reproductive success after recruitment in Kittiwakes. Reid et al (2003Reid et al ( , 2008 also found evidence of a relationship between early cohort conditions and future breeding success in Choughs (Pyrrhocorax pyrrhocorax), or between natal location and adult survival. In other words, there is substantial heterogeneity in results according to the species, study design and methods used to collect or analyze data.…”