Effects of Age and Culling on Movements and Dispersal Rates of Yellow-Legged Gulls (Larus michahellis) from a Western Mediterranean Colony

Abstract

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High philopatry rates of Yellow-legged Gulls in the southeastern part of the Bay of Biscay

“…By contrast, other smaller gulls, such as the Black-legged Kittiwake (Rissa trydactyla), were shown to have much smaller local recruitment rates, ranging between 35 and < 10% (Porter and Coulson 1987;Coulson and Coulson 2008;McKnight et al 2019). Estimates for the Herring Gull (Larus argentatus) have also reported considerably low local recruitment rates (< 40%) (Chabrzyk and Coulson 1976;Parsons and Duncan 1978), though in this case the cull of breeding birds could have promoted philopatry rates values abnormally high (Bosch et al 2000(Bosch et al , 2019. The effect of external factors like culling programs on recruitment is important, and the values from some colonies may not be extrapolated to other colonies since this would lead false premises in demographic models (Brooks and Lebreton 2001).…”

“…If we call this last concept 'local' recruitment, it can be then stated as a synonym of philopatry. The local recruitment among close-by wellestablished colonies has been one of the least known aspects on seabird biology (Gaston 2004), though the body of studies dealing with this subject is increasing (Bosch et al 2019;Davis et al 2019;McKnight et al 2019). The analysis of local recruitment rates in colonial seabirds is called to play a very relevant role in our comprehension of the dynamics and demographic factors driving seabird populations (Spear et al 1998;Cam et al 2002;Payo-Payo et al 2015).…”

“…In such a scenario, gulls would be expected to show high local recruitment rates, as they would tend to show a high degree of philopatry to those colonies where they find cues indicating good conditions (Gaston 2004). Previous research with the species has assessed local recruitment rates under scenarios where culling programs were active (Bosch et al 2000(Bosch et al , 2019 or using reference estimates from other gull species of similar ecology (Brooks and Lebreton 2001), but where, again, the colonies were subject of culling (Chabrzyk and Coulson 1976;Parsons and Duncan 1978). Therefore, there is still a gap of knowledge on this topic.…”

Immigration allows population persistence and maintains genetic diversity despite an attempted experimental extinction

“…Our current study highlights the role of immigration in maintaining genetic diversity and allowing population persistence in the face of even extreme and lengthy demographic pressures, further supporting the importance of patch connectivity for both demographic and genetic resilience. Although other studies have demonstrated the ability of immigration to counter high local mortality in populations, including from lethal culling of managed populations [ 69 , 70 ], our study represents an extreme case of severe population reduction (all observed adults removed from the population) occurring long term (over eight consecutive generations), and represents a particularly strong test of the ability of immigration to maintain local populations.…”