Climatic dipoles drive two principal modes of North American boreal bird irruption

Abstract

Pine Siskins exemplify normally boreal seed-eating birds that can be sparse or absent across entire regions of North America in one year and then appear in large numbers the next. These dramatic avian "irruptions" are thought to stem from intermittent but broadly synchronous seed production (masting) in one year and meager seed crops in the next. A prevalent hypothesis is that widespread masting in the boreal forest at high latitudes is driven primarily by favorable climate during the two to three consecutive years required to initiate and mature seed crops in most conifers. Seed production is expensive for trees and is much reduced in the years following masting, driving boreal birds to search elsewhere for food and overwintering habitat. Despite this plausible logic, prior efforts to discover climate-irruption relationships have been inconclusive. Here, analysis of more than 2 million Pine Siskin observations from Project FeederWatch, a citizen science program, reveals two principal irruption modes (North-South and WestEast), both of which are correlated with climate variability. The North-South irruption mode is, in part, influenced by winter harshness, but the predominant climate drivers of both modes manifest in the warm season as continental-scale pairs of oppositely signed precipitation and temperature anomalies (i.e., dipoles). The climate dipoles juxtapose favorable and unfavorable conditions for seed production and wintering habitat, motivating a push-pull paradigm to explain irruptions of Pine Siskins and possibly other boreal bird populations in North America.avian irruption | boreal birds | climate variability | migration | masting

The response of migratory populations to phenological change: a Migratory Flow Network modelling approach

“…Jacoby et al 2012). The MFN is a mathematical expression of the push-pull paradigm of migration (Strong et al 2015) and expresses the idea that animals move between regions at a rate proportional to the difference in the pressure at the source ('push') and the pressure at the destination ('pull') divided by the resistance to movement. Pressure is in turn negatively or inversely related to attractiveness.…”

Climate teleconnections synchronizePicea glaucamasting and fire disturbance: Evidence for a fire‐related form of environmental prediction

“…As these climate patterns affect all phenomena simultaneously and force them to fluctuate in synchrony (Liebhold, Koenig, & Bjørnstad, ), direct and indirect interactions between organisms and their physical environment emerge (Forchhammer & Post, ). So for instance, teleconnections affect both natural disturbance regimes (Mariani et al, ; Shabbar & Skinner, ) and yearly to decadal fluctuations in large‐scale reproduction pulses in seed‐masting species (Ascoli, Vacchiano, et al, ; Chechina & Hamann, ; Strong, Zuckerberg, Betancourt, & Koenig, ; Williamson & Ickes, ). In‐phase fluctuations of seed pulses and disturbance have important consequences for the regeneration dynamics of masting species.…”

Opportunities and challenges for big data ornithology

“…For example, estimates of bird occurrence or abundance (eBird) or of migration intensity (WSR) can be used to address how bird populations are affected by extreme weather events (e.g., heat waves, droughts, tornadoes, and hurricanes; Albright et al 2010aAlbright et al , 2010b or human-caused natural disasters (e.g., oil spills or wildfires). One example that represents the real-time potential of these efforts is a study that examined the climatic drivers of Pine Siskin (Spinus pinus) irruptive migration in North America (Strong et al 2015). This study used 2 million Pine Siskin observations from the Project FeederWatch citizen science program (https://feederwatch.org/), which monitors the occurrence and abundance of wintering birds at supplemental feeders in North America, to assess how irruptions were correlated with climatic variability.…”