A comparison of stopover behaviour of two subspecies of the bluethroat Luscinia svecica in northern Iberia during the autumn migration period

Doi: http://dx.doi.org/10.13157/arla.58.2.2011.251

Authors: Juan ARIZAGA, Agustín MENDIBURU, Daniel ALONSO, Juan F. CUADRADO, Jose I. JAUREGI and Juan M. SÁNCHEZ

Published: Volume 58(2), December 2011. Pages 251-266.

Language: English

Keywords: Cormack-Jolly-Seber models, fuel deposition rate, fuel load, stopover duration, tidal marsh and Txingudi

Summary:

Iberia offers one of the last opportunities four migrants to refuel before crossing the Sahara. It is also a destination for populations that overwinter within the circum-Mediterranean region. Our aim was to analyse whether two bluethroat subspecies that stop over in northern Iberia and face different migration distances, show different stopover behaviour in terms of periods of passage, fuel management and stopover duration. The subspecies were Luscinia svecica namnetum, which overwinters within the circum-Mediterranean region; and L. s. cyanecula, some of which migrate to tropical Africa. Overall, we obtained 265 captures, involving 208 distinct bluethroats and 56 recaptures, at the Txingudi marshlands in northern Iberia, during the autumn migration periods of 2007 and 2008. Passage periods did not differ between both subspecies, nor did fuel load (body mass: 15.0 g; fat: 1.0), mass depositionrate (0.07 g/day) and stopover duration (15.3 days). However, late L. s. cyanecula showed higher fuel loads than early individuals, so these birds could potentially cover longer distances without needing to refuel. Mean fat score was low for both subspecies which, together with the very low rate of fuel accumulation, supports the hypothesis that Iberia is crossed in consecutive short steps. Long-distance L. s. cyanecula migrants could acquire the high fuel loads needed to migrate to tropical Africa in southern Iberia or north-western Africa.

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