The importance of range edges for an irruptive species during extreme weather events Brooke L. Bateman, Anna M. Pidgeon, Volker C. Radeloff, Andrew J. Allstadt, H. Resit Akçakaya, Wayne E. Thogmartin, et al. Landscape Ecology ISSN 0921-2973 Landscape Ecol DOI 10.1007/s10980-015-0212-6 1 23 Your article is protected by copyright and all rights are held exclusively by Springer Science +Business Media Dordrecht. This e-offprint is for personal use only and shall not be self- archived in electronic repositories. If you wish to self-archive your article, please use the accepted manuscript version for posting on your own website. You may further deposit the accepted manuscript version in any repository, provided it is only made publicly available 12 months after official publication or later and provided acknowledgement is given to the original source of publication and a link is inserted to the published article on Springer's website. The link must be accompanied by the following text: "The final publication is available at link.springer.com”. 1 23 Author's personal copy Landscape Ecol DOI 10.1007/s10980-015-0212-6 RESEARCH ARTICLE The importance of range edges for an irruptive species during extreme weather events Brooke L. Bateman . Anna M. Pidgeon . Volker C. Radeloff . Andrew J. Allstadt . H. Resit Akc¸akaya . Wayne E. Thogmartin . Stephen J. Vavrus . Patricia J. Heglund Received: 2 January 2014 / Accepted: 9 May 2015 Ó Springer Science+Business Media Dordrecht 2015 Abstract abundances in the core and edge regions to the Context Threats to wildlife species from extreme standardized precipitation evapotranspiration index, a events, such as droughts, are predicted to increase in measure of drought, in linear regressions. frequency and magnitude with climate change. Ex- Results We found that Dickcissel irruptions in the treme events can cause mortality and community-level northern range edges were related to drought condi- changes, but for some mobile species, movement tions in the range core, potentially a consequence of away from areas affected may be a viable option. birds being ‘pushed’ to the range edge when weather Objectives We examined the effect of extreme was unsuitable. Specifically, Dickcissels moved into weather on spatial patterns of abundance for an refuge sites containing a high proportion of cultivated irruptive grassland bird species, the Dickcissel (Spiza crops, with higher vegetation greenness, than those americana). areas they leave during drought years. Methods We calculated route-level annual abun- Conclusions In a changing climate where more fre- dances and abundance anomalies from 1980 to 2012 quent extreme weather may be more common, conser- from North American Breeding Bird Survey data, and vation strategies for weather-sensitive species may classified the Dickcissel’s range into core and edge require consideration of habitat in the edges of species’ regions using these abundances. We then compared ranges, even though non-core areas may be unoccupied in ‘normal’ years. Our results highlight the conservation Electronic supplementary material The online version of importance of range edges in providing refuge from this article (doi:10.1007/s10980-015-0212-6) contains sup- extreme events, such as drought, and climate change. plementary material, which is available to authorized users. B. L. Bateman (&) Á A. M. Pidgeon Á S. J. Vavrus V. C. Radeloff Á A. J. Allstadt Center for Climate Research, University of Wisconsin- SILVIS Lab, Department of Forest and Wildlife Ecology, Madison, Madison, WI, USA University of Wisconsin-Madison, Madison, WI, USA e-mail: [email protected] P. J. Heglund Upper Midwest Environmental Sciences Center, United H. Resit Akc¸akaya States Fish and Wildlife Service, La Crosse, WI, USA Department of Ecology and Evolution, Stony Brook University, Stony Brook, NY, USA W. E. Thogmartin Upper Midwest Environmental Sciences Center, United States Geological Survey, La Crosse, WI, USA 123 Author's personal copy Landscape Ecol Keywords Drought Á Extreme weather Á Grassland 2012b). Extreme weather can also cause changes in birds Á Range edge Á Range core Á Refuges abundance, and ultimately communities (Thibault and Brown 2008; Albright et al. 2010a, b). Whether these abundance changes reflect movement or mortality is difficult to determine because weather events can have Introduction different effects on different species, depending on their life history traits (Jiguet et al. 2006; Albright Numerous species across many taxa are responding to et al. 2011; Cormont et al. 2011). For highly mobile recent changes in climate, shifting their ranges species, such as most birds, movement away from towards the poles and higher altitudes (Thomas and threat during extreme events may be a viable response, Lennon 1999; Parmesan and Yohe 2003; Root et al. even in the case of species that normally exhibit high 2003; Hitch and Leberg 2007; Chen et al. 2011). site fidelity (Martin et al. 2007). Movement may be an However, short-term processes such as climate vari- especially effective response for slowly evolving ability or extreme weather events are likely to have extreme events, such as droughts. Highly mobile bird immediate consequences for organisms (Thompson species could thus have an advantage during extreme et al. 2013). These short-term climate and weather conditions because they can move away from ad- conditions can have a strong influence on overall versely affected areas. population persistence (Gutschick and BassiriRad Individuals that do move in response to extremes 2003; Bateman et al. 2012b; Thompson et al. 2013) must decide not just when but also where to go (Dean and affect species’ population dynamics and spatial et al. 2009). The ‘push–pull’ hypothesis, originally distribution (Parmesan et al. 2000; Jentsch et al. 2007; developed to explain human migration (Fuguitt 1959), Jentsch and Beierkuhnlein 2008). However, the effects provides a useful framework to conceptualize the of extreme weather on species at broad scales are not responses of mobile species to extreme weather. well understood. How these events influence species Movement of a species outside of its core range could occurrence and persistence throughout the landscape be caused either by ‘push’ factors, with individuals is of particular concern for conservation planners. dispersing in response to poor conditions within their Climate change projections forecast increasing core range, or by ‘pull’ factors that attract individuals mean temperatures, and also a more variable climate into areas of better conditions, or by both. In migratory causing an increase in the frequency and magnitude of birds, the processes involved in the ‘push–pull’ extreme weather events (Ra¨isa¨nen 2002; Salinger hypothesis can be seen during molt-migration, a 2005; Jentsch et al. 2007; Rummukainen 2012; phenomenon in which birds molt at a location in Goodess 2013). This heightened variability may between their breeding and wintering range. This is include multi-year droughts, increased regional vari- where poor weather conditions causing low produc- ability in weather patterns, and short-term extreme tivity on the breeding grounds appear to ‘push’ birds weather events such as weeklong heat waves, single- out, leading to a staged migration as birds are ‘pulled’ day high rainfall events, and spring cold snaps (IPCC to areas with better productivity (Barry et al. 2009; 2007; Kunkel et al. 2008; Rahmstorf and Coumou Fox and Walsh 2012). Movement of species that 2011; Coumou and Rahmstorf 2012; IPCC 2012). require resources or habitats that are especially Insights into both the role of changes in climate (e.g. dependent on suitable weather conditions, such as long-term means) and of that of short-term variability seasonal or semi-permanent water sources, may (e.g., extreme weather) can provide a more complete respond more to ‘push’ pressures by moving away picture of how climate change affects bird species. from sub-optimal conditions. Such ‘push’ pressures For North America, a strong increase in the have been suggested as a mechanism for post-spring- frequency and severity of widespread droughts is migratory movement in relation to weather and predicted (Wehner et al. 2011; Dai 2013). Species extreme events in songbirds (Albright et al. 2010b) responses to such extreme events may occur locally, and waterfowl (Smith 1970; van Wijk et al. 2012). where changes may be reflected in adult survival or When ‘push’ pressures occur, birds may be pushed reproductive success or even cause population-level across large areas, especially when the pressures extirpations (Cormont et al. 2011; Bateman et al. themselves are widespread. Alternatively, species may 123 Author's personal copy Landscape Ecol concentrate in areas of higher-quality habitat within a 1930s, Dickcissel irruptions in the northern range edge matrix of lower quality habitat. For example, Snail (e.g. southern Wisconsin) coincided with the dustbowl Kites (Rostrhamus sociabilis) concentrate in ‘refuge’ drought years (Taber 1947), and Dickcissels simulta- areas that have better water conditions than the neously became scarce in the range core (i.e., Kansas) surroundings (Martin et al. 2007). To best conserve where this species is commonly abundant during non- species facing extreme weather events, it is necessary drought periods (Wooster 1935). In 1964, a Dickcissel to identify conditions ‘pushing’ species, and, more irruption in Wisconsin included an increase in density importantly, to identify the refuge sites