The impact of tree crops and temperature on the timing of frugivorous bird migration
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GLOBAL CHANGE ECOLOGY – ORIGINAL RESEARCH
The impact of tree crops and temperature on the timing of frugivorous bird migration Anna‑Maria Kanerva1 · Tatu Hokkanen2 · Aleksi Lehikoinen3 · Kai Norrdahl1 · Jukka Suhonen1 Received: 23 September 2019 / Accepted: 30 July 2020 © The Author(s) 2020
Abstract Migration has evolved to tackle temporal changes in availability of resources. Climate change has been shown to affect the migration dates of species, which raises the question of whether the variation in the timing of migration is climate or resource dependent? The relative importance of temperature and availability of food as drivers of migration behaviour during both spring and autumn seasons has been poorly studied. Here, we investigated these patterns in frugivorous and granivorous birds (hereafter frugivorous) that are assumed to postpone their autumn migration when there is plenty of food available, which may also advance upcoming spring migration. On the other hand, especially spring migration dates have been negatively connected with increasing temperatures. We tested whether the autumn and spring migration dates of eleven common frugivorous birds depended on the crop size of trees or ambient temperatures using 29 years of data in Finland. The increased crop sizes of trees delayed autumn migration dates; whereas, autumn temperature did not show a significant connection. We also observed a temporal trend towards later departure. Increasing temperature and crop sizes advanced spring arrival dates. Our results support the hypothesis that the timing of autumn migration in the frugivorous birds depends on the availability of food and is weakly connected with the variation in temperature. Importantly, crop size can have carry-over effects and affect the timing of spring arrival possibly because birds have overwintered closer to the breeding grounds after an abundant crop year. Keywords Interaction between birds and trees · Frugivorous birds · Granivorous birds · Migratory behaviour · Mutualism · Species interactions · Tree crop size
Introduction Each year, a large number of animals conduct migration journeys due to temporal changes in resources (Dingle 1996). In the boreal zone, the seeds of several tree species are an important but fluctuating food resource for migrating and wintering birds (Haila et al. 1986; Newton 2008; Meller et al. 2016). The year-to-year variation in food availability Communicated by David M. Watson. * Jukka Suhonen [email protected] 1
Department of Biology, University of Turku, 20014 Turku, Finland
2
Natural resources/Forest management, Natural Resources Institute Finland, PO Box 2, 00791 Helsinki, Finland
3
The Helsinki Lab of Ornithology, The Finnish Museum of Natural History, University of Helsinki, PO Box 17, 00014 Helsinki, Finland
affects the migration behaviour of some migratory species, such as frugivorous and granivorous (hereafter frugivorous) birds at northern latitudes (Haila et al. 1986; Fox et al. 2009; Lindén et al. 2011; Suhonen and Jokimäki 2015; Suhonen et al
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