Environmental Instability as a Motor for Dispersal: A Case Study from a Growing Population of Glossy Ibis

Abstract

Dispersal is a life-history trait directly affecting population dynamics and species range shifts and thus playing a prominent role in the response to climate change. Nonetheless, the relationship between extreme climatic events and dispersal has received little attention in birds. Here we focused on climatic, demographic and individual factors affecting the dispersal propensity of a major glossy ibis population. We performed a capture-resighting analysis on individuals born and observed at Doñana (South-West Spain) over fourteen years. We applied a multiple analytical approach to show that single-site capture-resighting estimates were a reliable index of dispersal propensity from the area. We focused on the emigration of Doñana-born individuals sporadically (transients) and regularly (residents) frequenting their natal area. Droughts during two out of 14 study years caused higher apparent dispersal rates, explaining most of the annual variation in these rates. The age structure of Doñana-born individuals resighted simultaneously locally and in Morocco in one week over the 2010 autumn confirmed that the 2005 drought boosted permanent emigration. As numbers increased steadily during non-drought years since the formation of the colony in 1996 to several thousand pairs, philopatry increased gradually, while transients probability appeared to be related to average breeding success. Age, sex, density, quality of foraging habitat and breeding success in the previous season were not found to directly affect apparent dispersal. Nonetheless, autumn sex ratio gradually switched from male (≈0.68) to female-skewed (≈0.44) by the end of the study period, suggesting that males and females respond differently to high densities reached in recent years. This study demonstrates the importance of extreme climatic events as a powerful motor for spread of species in expansion. Also, it suggests different factors drive emigration of individuals according to their amount of experience in the area (e.g. transients vs residents).

Dispersal and migration of a specialist waterbird: where do Eurasian Spoonbills (Platalea leucorodia) come to Hungary from?

“…Taken together, these movements may help juveniles, immatures and sub-adults to decide where to breed in the future (Pigniczki & Végvári 2015). Such behaviour was suspected also in immature Gannets (Morus bassanus) (Votier et al 2011) and Glossy Ibises (Plegadis falcinellus) (Santoro et al 2013).…”

Immigration enhances fast growth of a newly-established source population

“…After being extinct in Doñana for many decades, in 1996 seven breeding pairs of glossy ibis settled in a pond-system (50 ha) known as "Lucio de la FAO" (FAO hereon) (Santoro et al 2010(Santoro et al , 2013). Strong population growth followed, with more than 7,000 breeding pairs estimated in 2011 in the whole of Doñana.…”

“…Over the last 20 yr, other smaller breeding colonies have established in East (1993) andNortheast Spain (1996) (Mañez and Rendón-Martos 2009), in the Camargue, France (2006) (Kayser et al 2009), Argelia (1998 (Boucheker et al 2009), Southwest (1994, and North (2011) Morocco (Amezian et al 2012). Additionally, irregular breeding has occurred in Portugal (Noivo and Jara 2007), Italy (Brichetti 1986, Grussu 2004, and some other areas in Spain, France (Marion and Marion 2011) and Morocco, especially since 2005 when a severe drought prevented breeding in Doñana (Santoro et al 2013; details in Table S1). …”

“…Furthermore, from 1998 onwards ~10 000 chicks have been visually sexed according to tarsus shape (Figuerola et al 2006) with an error probability (range 0.01-0.2) dependent on year and ringer (see Santoro et al 2013 for details). Until 2002, the Natural Processes Monitoring Team of the EBD-CSIC made an accurate estimate of both population size and productivity by conducting exhaustive counts of nests and fledglings during banding operations, combined with counts from vantage points (details in Mañez and Rendón-Martos 2009).…”

“…Parameters were modeled separately in sequential steps to limit both the influence of the modeling order and limit the number of models (details in Appendix S2; see also Grosbois and Tavecchia 2003). According to previous analyses (Santoro et al 2013) both Visual Sexing and Correctness were fixed as depending on the cohort. As a general rule, throughout the model simplification process we retained the structure of models in which AIC c (Akaike Information Criterion corrected for small sample sizes) was at least two units lower than others.…”