Extreme variations in spring temperature affect ecosystem regulating services provided by birds during migration

Abstract

Abstract. Extreme weather is becoming more pronounced, making phenological patterns less predictable. Among the potential consequences, extreme weather may alter relationships of migratory birds with their seasonal food resources and thus impact valuable ecosystem regulating services (e.g., bird predation of herbivorous insects). Our goal was to quantify the effect of an extremely warm spring on these relationships in a U.S Midwest oak savanna. Average regional temperatures in the spring of 2009 coupled with record highs in 2010 (88C warmer) were the basis of a natural experiment for addressing our goal. In both springs we documented tree flowering and leaf-out phenology, related these to arrival and foraging behavior of the three most abundant migratory wood-warbler species (Parulidae), and quantified the effects of migratory bird foraging on insect density, size, and herbivory using a branch exclosure experiment. In 2009, the dominant tree species at our study site, eastern black oak (Quercus velutina), flowered in mid-May and the wood warblers foraged heavily in the savanna during this time. Branches from which birds were excluded exhibited a trend toward higher insect density, larger Lepidopterans, and greater flower damage than control branches. In 2010, tree phenology was four weeks earlier than in 2009 and the wood warblers were nearly absent from the savanna (83% fewer), likely because peak food availability preceded their arrival in mid-May. Insect density was 83% greater in 2009 than 2010. However, in 2010, 81% of sampled leaves exhibited substantial damage (.25% of leaf-area removed) compared with 27% of leaves in 2009, presumably due to a lack of herbivorous insect regulation by birds. Our results suggest that the extremely warm spring of 2010 altered linkages between migratory birds and their invertebrate prey that are typical during years of average weather, which likely affected habitat use and the delivery of ecosystem regulating services.

Wintering in Europe instead of Africa enhances juvenile survival in a long-distance migrant

“…Nevertheless, if such an evolutionary gap exists, the plastic nature of bird migration (Able & Belthoff, 1998;Alerstam et al, 2003;Pulido & Berthold, 2010) is expected to lead to a decrease in long-distance migratory behaviour, as has been reported extensively in recent years (Ambrosini et al, 2016;Gordo et al, 2007;Newton, 2008;Pav on-Jord an et al, 2015;Ramo et al, 2015). Migratory shift, unless mitigated by density-dependent effects (Musilov a, Musil, Zouhar, & Romportl, 2015), may have a profound impact on migrants' population ecology with implications for abandoned and newly utilized ecosystems (Uno & Power, 2015;Wood & Pidgeon, 2015). However, caution should be taken when drawing such conclusions based on our case study as the results deal only with first-year juveniles and the data, despite their high quality and resolution, came from a rather modest number of individuals (especially for EUW storks).…”

Holding steady: Little change in intensity or timing of bird migration over the Gulf of Mexico

“…We predict the magnitude of phenological change increases with increasing latitude across North America during spring movements. Yet, while adjustments to stopover duration can be made, the growing divide between resource availability and migration initiation may stretch the limit of this phenotypic plasticity (Schmaljohann & Both, 2017), resulting in insufficient adjustments and possibly trophic mismatches (Strode, 2015;Wood & Pidgeon, 2015). Numerous studies of plot-level phenology demonstrate that variation in phenology of individual plant species is impactful for migrant phenology (Strode, 2009;Wood, Pidgeon, Liu, & Mladenoff, 2012).…”

Fuel loads acquired at a stopover site influence the pace of intercontinental migration in a boreal songbird

“…Migration is still the least studied period of the annual cycle of most migratory birds despite accumulating evidence suggesting that it is a critical period that can impact population dynamics 5, 48, 69, 76 (but see ref. 77).…”