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# Climate change effects on tropical birds

Authors:
Author's personal copy
Review
The effects of climate change on tropical birds
Çag
˘an H. Sßekerciog
˘lu
a,b,
, Richard B. Primack
c
, Janice Wormworth
d
a
Department of Biology, University of Utah, 257 South, 1400 East, Salt Lake City, UT 84112-0840, USA
b
KuzeyDog
˘a Derneg
˘i, _
Istasyon Mah., 36200 Kars, Turkey
c
Biology Department, Boston University, Boston, MA 02215, USA
d
6-16 St. Neot Ave., Potts Point, NSW 2011, Australia
a r t i c l e i n f o
Article history:
Received in revised form 12 October 2011
Accepted 17 October 2011
Available online 22 February 2012
Keywords:
Avian ecology
Biodiversity hotspots
Climate change
Conservation
Deforestation
Endemism
Evolution
Global warming
Ornithology
REDD
Tropical biology
a b s t r a c t
Birds are among the most widely studied organisms on earth and represent an important indicator group
for learning about the effects of climate change – particularly in regard to the effects of climate change on
tropical ecosystems. In this review, we assess the potential impacts of climate change on tropical birds
and discuss the factors that affect species’ ability to adapt and survive the impending alterations in hab-
itat availability. Tropical mountain birds, species without access to higher elevations, coastal forest birds,
and restricted-range species are especially vulnerable. Some birds may be especially susceptible to
increased rainfall seasonality and to extreme weather events, such as heat waves, cold spells, and tropical
cyclones. Birds that experience limited temperature variation and have low basal metabolic rates will be
the most prone to the physiological effects of warming temperatures and heat waves. Mostly unknown
species’ interactions, indirect effects, and synergies of climate change with other threats, such as habitat
loss, emerging diseases, invasive species, and hunting will exacerbate the effects of climate change on
tropical birds. In some models habitat loss can increase bird extinctions caused by climate change by
50%. 3.5 °C surface warming by the year 2100 may result in 600–900 extinctions of land bird species,
89% of which occur in the tropics. Depending on the amount of future habitat loss, each degree of surface
warming could lead to approximately 100–500 additional bird extinctions. Protected areas will be more
important than ever, but they need to be designed with climate change in mind. Although 92% of
currently protected areas are likely to become climatically unsuitable in a century, for example only 7
or 8 priority species’ preferred climatic envelopes are projected to be entirely lost from the African
Important Bird Area network. Networks of protected areas need to incorporate extensive topographical
diversity, cover wide elevational ranges, have high connectivity, and integrate human-dominated
landscapes into conservation schemes. Most tropical bird species vulnerable to climate change are not
currently considered threatened with extinction, often due to lack of knowledge; systematically and
regularly gathering information on the ecology, and current and future distributions of these species is
an urgent priority. Locally based, long-term tropical bird monitoring and conservation programs based
on adaptive management are essential to help protect birds against climate change.
Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Geography, habitat and range shifts: which species will be most affected? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2.1. Montane species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.2. Species of tropical coastal and island ecosystems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.3. Birds in extensive lowland forests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.4. Birds in non-forest habitats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.5. Aquatic birds in the tropics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.6. Arid zone species. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.7. Birds in human-dominated landscapes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
0006-3207/$- see front matter Ó2012 Published by Elsevier Ltd. doi:10.1016/j.biocon.2011.10.019 Abbreviations: BMR, basal metabolic rate; IBA, Important Bird Area; IPCC, Intergovernmental Panel on Climate Change; NPP, net primary productivity. Corresponding author at: Department of Biology, University of Utah, 257 South, 1400 East, Salt Lake City, UT 84112-0840, USA. Tel.: +1 801 585 1052. E-mail address: c.s@utah.edu (Ç.H. Sßekerciog ˘lu). Biological Conservation 148 (2012) 1–18 Contents lists available at SciVerse ScienceDirect Biological Conservation j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / b i o c o n Author's personal copy 2.8. Projected impacts of range shifts on tropical birds. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.9. Manakins: a case study. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3. Evolution and adaptation: slow lives in a fast-paced new world . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3.1. How physiology and microclimate impact tropical bird species’ ability to adapt. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.2. Basal metabolic rate in tropical birds: implications for survival . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 4. Role of mobility and migration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 5. Interspecific interactions and indirect effects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 5.1. Ecosystem functions and services . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 6. Destructive synergies: climate change exacerbates other environmental stressors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 6.1. Habitat loss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 6.2. Hunting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 6.3. Invasive species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 6.4. Emerging diseases and shifting disease vectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 7. Seasonality and variability. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 7.1. Extreme weather events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 8. Discussion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 8.1. Future projections and models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 8.2. The need for more tropical research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 8.3. The value of protected areas for tropical birds: planning for future change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 8.4. Research and management. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 1. Introduction Climate change is increasingly recognized, along with habitat destruction, as one of the most serious and widespread threats to biological diversity (IPCC, 2007). As scientists search for the best biological indicators of human-induced climate change, birds offer two advantages: ﬁrst, they are the best-known class of organisms when it comes to climate research (Wormworth and Sßekerciog ˘lu, 2011), and second, millions of citizen-scientist birdwatchers track them across the globe, contributing to extensive datasets (Kinzelbach, 1995;www.ebird.org;www.worldbirds.org). For example, the arrival dates of migratory birds feature prominently in the long phenological records of Europe, in part thanks to natural- ists like Robert Marsham who began compiling ‘Indications of Spring’ in 1736 (Lehikoinen et al., 2004). As a well-studied, globally-distributed indicator group, birds’ are excellent bellwethers of climate change effects on biodiversity. Bird distributional shifts have already been linked to climate change (Gregory et al., 2009; Niven et al., 2009; Chen et al., 2011). Un- checked climate change, combined with habitat loss, may lead to the extinctions of hundreds of bird species (Sßekerciog ˘lu et al., 2008). Tropical bird species’ particular vulnerability to climate change is increasingly recognized (La Sorte and Jetz, 2010; Harris et al., 2011; Sodhi et al., 2011; Wormworth and Sßekerciog ˘lu, 2011). Most tropical birds are sedentary, endemic species isolated on tropical mountains (Janzen, 1967; Sßekerciog ˘lu et al., 2008) and lowland species without access to higher elevations (Loarie et al., 2009) are likely to face greater risk. However, there are few studies of climate change effects on the bird communities of entire tropical forest regions (Harris et al., 2011), and few tropical bird families have been assessed in their entirety (see the case study, section 2.9). Yet information on current and predicted climate change im- pacts on tropical birds could be used to evaluate the suitability of current conservation practices, such as the adequacy of existing protected area networks, and to suggest management strategies to prevent the future decline and extinction of these species. Many physiological, ecological, and biogeographical characteristics that make certain bird species more susceptible to climate change are also present in non-avian groups. Ongoing measures and manage- ment regimes to reduce climate change threats to bird communi- ties could also help species in other groups. With these in mind, we have conducted an extensive review of the literature on the effects of climate change on tropical birds. We searched the Web of Knowledge™ with the keywords climat AND chang AND bird and their variations. We focused on the studies on tropical birds and also read the relevant articles cited in and cit- ing these articles. In a few cases, where tropical examples were not available, we gave temperate examples of phenomena that should be watched for in tropical systems. Two of us (ÇHSßand JW) spent the past two years reviewing and summarizing the literature on climate change effects on birds for a recent book (Wormworth and Sßekerciog ˘lu, 2011). Our main goals are to outline the existing and potential effects of climate change on tropical bird communities, to examine why certain bird species are more susceptible to climate change, and to discuss how this information can be used to improve the conser- vation and management of birds and other taxa in the face of esca- lating climate change. 2. Geography, habitat and range shifts: which species will be most affected? This section outlines how certain geographical (e.g. mountains) and habitat (e.g. forests) features are likely to interact with climate change to affect tropical birds. It also discusses modeled results of range shifts due to climate change, and their consequences for birds. Despite the uncertainties in predicting precipitation changes in the tropics, multiple models based on the IPCC A2 Emissions Sce- nario predict tropical drying trends, ‘‘in relatively intense, localized regions at the margins of the convection zones’’ particularly in the Caribbean/Central America region and equatorial South America (Neelin et al., 2006). Although overall tropical drying trends com- prise a signiﬁcantly larger fraction of the average changes in rain- fall, some locations will experience more precipitation, including the equatorial Paciﬁc region of the convection zones, and increased Southeast Asian summer monsoon (Neelin et al., 2006). Temperature increase is the main driver of climate change- caused habitat loss at higher elevations, whereas precipitation changes are the main cause in lowlands (Enquist, 2002; Li et al., 2009). Because endemism is greater at higher elevations in the tropics (Enquist, 2002), temperature has a greater effect on tropical 2Ç.H. Sßekerciog ˘lu et al. / Biological Conservation 148 (2012) 1–18 Author's personal copy vertebrate ranges than does precipitation (McCain, 2009). Temper- ature, through its effects on evapotranspiration and NPP, also has a crucial effect on vegetation change in the tropics (Delire et al., 2008) and temperature increases are likely to have a greater impact in the loss of tropical endemics than are changes in precipitation. However, past changes in bird communities suggest that major changes in precipitation patterns, such as changes in the monsoon regime, may be more important than temperature changes, particularly if warming is limited to 2 °C (Tyrberg, 2010). 2.1. Montane species Tropical mountain species are among birds most vulnerable to climate change (Sßekerciog ˘lu et al., 2008; Wormworth and Sßeker- ciog ˘lu, 2011). Extinction risk increases as birds’ elevational ranges narrow (Fig. 1). In addition, a given elevational range translates into a much smaller area of occupancy at the top of a mountain compared to its base; for example, the top and bottom one-meter bands of a hundred-meter tall square pyramid differ in area by two orders of magnitude. Where warming temperatures reduce many montane species ranges’ by forcing them to shift upslope, some species may be driven to local (or global) extinction, particularly species endemic to tropical highlands (Shoo et al., 2005a; Colwell et al., 2008; Gasner et al., 2010; La Sorte and Jetz, 2010;Figs. 2 and 3). Conversely, bird species with access to intact habitats span- ning a wide elevational range are expected to be less affected by climate change (Anciaes and Peterson, 2009). Despite the impor- tance to estimates of tropical birds extinctions, few data exist on the potential extent and magnitude of current and future shifts in tropical birds’ elevational limits in response to climate change (Bohning-Gaese and Lemoine, 2004; Laurance et al., 2011; Shoo et al., 2006; e.g. Figs. 2 and 3). Yet, studies of ‘disappearing cli- mates’ further emphasize the threats to birds of tropical moun- tains. Areas with disappearing climates are expected to be concentrated at the poleward regions of continents, but also in tropical mountain regions, including areas that correspond to bio- diversity hotspots (Williams et al., 2007). In this regard, tropical mountain cloud forests deserve special mention for the dispropor- tionately high and concentrated biodiversity they host. For exam- ple, widespread epiphytes provide birds with food and nesting materials. However, these plants occupy ﬁne-grained climate niches on tree trunks, crooks and branches, and epiphyte mortality can occur under even slight climatic change, with cascading effects on cloud forest communities. With warming, many cloud forests can be expected to experience reduced cloud cover, less water capture and drier ecosystems (WTMA, 2008; Karmalkar et al., 2008) as current climate conditions shift upslope. In the IPCC report, Fischlin et al. (2007) emphasized that tropical mountain cloud forests are among the tropical forest regions where endemics are at ‘‘disproportionately high risk of extinction’’. Elevational distribution is often used as a proxy for population size. However, in the Wet Tropics of Queensland, highland bird populations (e.g. Fig. 2) may decline even more quickly than sug- gested by warming-induced range contractions (Shoo et al., 2005b). For most bird populations, their abundance is unlikely to be distributed uniformly across their ranges and across different elevations. Although climate-change induced alterations in abun- dance patterns have important conservation implications, these changes have not been well studied (Shoo et al., 2005b). Also little understood are potential increases in net primary productivity that may partially ameliorate some of projected impacts of global warming on the biodiversity of tropical highlands (Williams et al., 2010). Hotter lowland zones tend to isolate the populations of upland tropical birds, which are often sedentary (Janzen, 1967). Tropical montane endemics like Venezuela’s endangered scissor- tailed hummingbird (Hylonympha macrocerca) or regal sunbird (Nectarinia regia) of East Africa (Fig. 3) have limited capacity to shift their ranges across such unsuitable habitat to other mountain ranges, which could make such birds particularly vulnerable to extinction from climate change. Yet, because tropical mountains tend to have low human populations and more intact habitat rel- ative to tropical lowlands, most tropical montane bird species, like golden bowerbirds (Prionodura newtoniana), have been considered to be of least conservation concern – but now face the looming threat of climate change (Sßekerciog ˘lu et al., 2008; Shoo et al., 2005a;Fig. 2). Due to limited data, climate change is only recently being incorporated into the assessments of extinction likelihood (BirdLife International, 2008), but it is increasingly realized that 0 10 20 30 40 50 60 70 80 2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 3.8 Log of elevational range Landbrid species currently at risk of extinction (%) Fig. 1. The relationship between bird extinction risk and elevational range (r 2 = 0.97, p< 0.0001). The x-axis is the log 10 of each species’ elevational range rounded up to the nearest hundred meters (upper elevational limit – lower elevational limit). For example, the point corresponding to 2 (=log of 100 m) on the x-axis means that of the 79 bird species that have elevational ranges that are 6100 m, 72% are threatened or near threatened with extinction. Reprinted with permission from Sßekerciog ˘lu et al. (2008). Climate change, elevational range shifts, and bird extinctions. Conservation Biology 22, 140–150. Fig. 2. Predicted area of golden bowerbird habitat in a number of future climate change scenarios including a range of changes in rainfall and from one to three degrees of warming. Reprinted with permission from Elsevier, David W. Hilbert and CSIRO. Hilbert et al. (2004) Golden bowerbird (Prionodura newtonia) habitat in past, present and future climates: predicted extinction of a vertebrate in tropical highlands due to global warming. Biological Conservation 116, 367–377. Ç.H. Sßekerciog ˘lu et al. / Biological Conservation 148 (2012) 1–18 3 Author's personal copy in the long term, ‘‘it may be the most serious threat of all’’ (BirdLife International, 2008; Hilton-Taylor et al., 2009). 2.2. Species of tropical coastal and island ecosystems Effects of climate change on tropical coastal forests, such as mangrove forests, are even less known. Tropical coastal ecosys- tems are disappearing at a rapid rate and are highly sensitive to both climate change and concomitant sea level rise (Waycott et al., 2009). The loss of these coastal habitats should concern us greatly because they provide key ecosystem functions and services (Sßekerciog ˘lu, 2010a), such as reducing the damage caused by tsunamis. Tropical forests and bird communities on oceanic islands are especially vulnerable to climate change. More than any other hab- itat, these communities have already suffered greatly from intro- duced invasive species and exploitation (BirdLife International, 2011). Island ecosystems have been drastically modiﬁed, and most still experience ongoing habitat loss. This includes the loss of land area due to rising sea levels resulting from global climate change (Kingsford et al., 2009). Coastal ﬂooding is likely to reduce the ex- tent of coastal wetlands on small islands, and increases in the num- ber of extreme events, including a possible increase in the number of intense tropical cyclones, could degrade tropical forests that are often small in extent, and may be slow to regenerate (Mimura et al., 2007). Many threatened tropical island endemics such as the critically endangered mangrove ﬁnch (Camarhynchus helio- bates) on the Galapagos Islands, endangered Abbott’s booby (Papa- sula abbotti) on Christmas Island, and critically endangered Cozumel thrasher (Toxostoma guttatum) of Mexico now face the additional threat of climate change. Tropical seabirds reliant on coastal zones and islands are also vulnerable, particularly during the breeding season (e.g. Ancona et al., 2011). Tropical seabirds of Australia’s Great Barrier Reef are vulnerable not just to warming events that affect their foraging success (Peck et al., 2004; Erwin and Congdon, 2007), but also to sea level rise that could inundate the low-lying coral cays which host their breeding colonies. Most cays are less than three metres above the high water mark, and low-lying cays, which are pre- ferred by most seabirds, could be ﬂooded in the future during storm surges or even at high tide (Hulsman & Devney, 2010). 2.3. Birds in extensive lowland forests For species in extensive low-lying areas such as the Amazon and Congo basins, where topographical diversity is lacking, climate change poses an additional challenge. As climate warms, many types of vegetation and dependent organisms – including fruit trees and insects that many birds depend on – may be expected to shift their distributions to track their preferred microclimates. Broadly speaking, this would entail dispersal toward the poles or to higher altitudes (Gregory et al., 2009; Janzen, 1967; Niven et al., 2009; Pounds et al., 1999; Shoo et al., 2006). Where upslope shifts are made possible due to the proximity of mountains, this may require relatively short dispersal distances for vegetation and dependent species. Yet in extensive ﬂat areas, where mountains are few and far between, such as the Amazon basin and the Congo basin, plant and animal communities may need to move far greater distances to track their climate preferences (Anciaes and Peterson, 2009; Loa- rie et al., 2009; Menon et al., 2009; Peterson et al., 2002, 2001; Sßekerciog ˘lu et al., 2008). Poor dispersers, such as birds of the forest interior (e.g., endangered Congo peafowl, Afropavo congensis and vulnerable rufous twistwing, Cnipodectes superrufus), may not be able to make these range shifts. Furthermore, tropical lowland com- munities may experience net biotic attrition, as a result of the spe- cies moving to higher elevations not being replaced by other species (Colwell et al., 2008). 2.4. Birds in non-forest habitats Although relevant studies of tropical birds have mainly focused on forest species (e.g. Pounds et al., 1999; Shoo et al., 2005a), thou- sands of tropical bird species inhabit diverse open habitats such as savanna, cerrado, grasslands, karoo, scrub, deserts, and human- dominated areas. Recently, Marini et al. (2009) modeled the ex- pected effects of climate change on the distributions of 26 wide- spread bird species of the cerrado. This ecosystem has the largest extent of tropical savanna worldwide, and 44% of its approximately 10,000 plant species are endemic. Projected range size contractions of up to 80% will affect various savanna (e.g. near threatened coal- crested ﬁnch, Charitospiza eucosma) and grassland (e.g. vulnerable lesser nothura, Nothura minor) species, and species with smaller ranges (Marini et al., 2009). Range shifts of 175–200 km towards southeastern Brazil are predicted, but the dispersal of species could be thwarted because that region has high levels of human popula- tion and development (Marini et al., 2009). Extensive deforestation of the Brazilian Atlantic forest further exacerbates the effects of cli- mate change (Loiselle et al., 2010). 2.5. Aquatic birds in the tropics Climatic models have focused mainly on terrestrial species. However, the diversity patterns of aquatic birds such as waders, ducks, and geese differ from those of terrestrial bird species (Ramirez-Bastida et al., 2008). Coastal regions, which often have high bird diversity, will be affected by rising sea levels. Yet, Fig. 3. Modeled future range of regal sunbird (Nectarinia regia). Reprinted with permission from BirdLife International (2008) Groundbreaking work will help Africa’s biodiversity combat climate change. URL: http://www.birdlife.org/news/news/2008/07/rwanda_meeting.html. 4Ç.H. Sßekerciog ˘lu et al. / Biological Conservation 148 (2012) 1–18 Author's personal copy because coastal wetlands are often bounded by agriculture and set- tlements, opportunities for range shifts are limited. These wetlands include Florida’s Everglades and its globally important colonies of roseate spoonbills (Platalea ajaja), wood storks (Mycteria ameri- cana), and other waterbirds. Vast coastal swamps in northern Australia are also at risk, including Kakadu, which harbors more than 280 bird species. Only marginally above sea level, these trop- ical wetlands have already proven to be vulnerable to salt water incursion. Yet this region’s sea level rise is currently occurring at four times the global average rate. Exacerbated by tropical storms, sea level rise could cause these highly productive wetland areas to be transformed into salt pans, greatly degrading their potential to host bird populations (Traill et al., 2010; Garnett and Brook, 2011). On the other hand, salt-tolerant coastal marshes are likely to ex- pand and this could beneﬁt the species that prefer these wetlands. Birds of peat swamp forests are also of concern. Of all forest types, peat swamp forests are the most vulnerable to ﬁres, partic- ularly during droughts and El Niño years (Posa et al., 2011). These ﬁres can take months to extinguish. They also exacerbate climate change by causing the release of massive amounts of carbon stored in these peat forests, adding to the global greenhouse gas burden. Unfortunately, no global analyses have been undertaken to model the expected changes in tropical wetland/coastal habitats in response to climate change scenarios. Additional factors such as hunting, disease, and habitat loss further threaten tropical wet- land species (Traill et al., 2009, 2010). Given their dependence on water, tropical aquatic birds will be particularly vulnerable to cli- mate change. 2.6. Arid zone species Arid zone species, such as desert cisticola (Cisticola aridulus), are assumed to be resilient to high temperatures and low humidity. However, these species are already exposed to extreme conditions and are often dependent on seasonal rains, as well as on aquatic habitats such as riparian forests, seasonal and permanent water- holes, lakes, and rivers (Schneider and Griesser, 2009). We have limited knowledge of how future changes in temperature may af- fect rainfall patterns, and how further increases in already high temperatures and/or changes in rainfall regimes may affect the availability of other sources of water and food. The disappearance of water sources is likely to be devastating for these ‘‘oasis’’ com- munities, and the added stress of higher temperatures and possibly scarcer rainfall could test the tolerances of even these seemingly hardy species. Even small temperature increases can greatly increase the amount of birds’ evaporative water loss. Hotter weather due to climate change is expected to test the ability of desert birds to sustain their water balance, and climate change is expected to lead to more frequent episodes of catastrophic mortal- ity by the 2080s. Modeling suggests that small desert birds will require 150–200% more water during the hottest period of the day to survive predicted increases in maximum daily temperature (McKechnie and Erasmus, 2006; McKechnie and Wolf, 2010). 2.7. Birds in human-dominated landscapes Ecologists tend to focus their studies on relatively intact ecosys- tems, but this limits our ability to predict climate change impacts on human-dominated ecosystems (Felton et al., 2009). Because human-dominated lands make up a large and growing subset of tropical ecosystems, it would be worthwhile to gather more data about birds that are impacted by human activity. Some human activities and human-dominated areas can be modiﬁed to allow birds to survive, and research may identify the changes needed to foster this. For example, some forest birds, such as silver-throated tanagers (Tangara icterocephala), orange-billed nightingale-thrushes (Catharus aurantiirostris), and white-throated thrushes (Turdus assimilis) persist in the agricultural landscapes of southern Costa Rica by either adapting to coffee plantations or by focusing their activities on remnant trees, riparian strips, and small forest fragments (Sßekerciog ˘lu et al., 2007). As human-dominated ecosystems increasingly surround intact ecosystems, improving the conservation capacity of human-dominated tropical country- side will be critical. This will include increases in landscape connec- tivity and other improvements that optimize the potential for species to carry out range shifts in response to climate change. 2.8. Projected impacts of range shifts on tropical birds Modeled shifts in species’ ranges in the Neotropics indicate that those in the tropical parts of the Mexican and Andean mountains, and in the biodiversity hotspot of Central America could be the most affected by climate change (Lawler et al., 2009). In 80% of cli- mate change scenarios, these regions are expected to lose 25–38% of their endemic species (Lawler et al., 2009). The Brazilian Atlantic forests and the southern and western boundaries of the Brazilian cerrado are also likely to experience high species turnover. Hun- dreds of restricted-range species are expected to be at the risk of extinction as a result of climate change (Lawler et al., 2009). Cli- mate change is likely to exacerbate the conservation status of this region’s already threatened bird species, such as the endangered horned guan (Oreophasis derbianus) in the cloud forests of Mexico and Guatemala, endangered Cochabamba mountain-ﬁnch (Comp- sospiza garleppi) in the Bolivian Andes, vulnerable red-fronted par- rotlet (Touit costaricensis) in Costa Rica and Panama, critically endangered kinglet calyptura (Calyptura cristata) in the Brazilian Atlantic forest, and also critically endangered blue-eyed ground- dove (Columbina cyanopis) in the Brazilian cerrado. In sub-Saharan Africa, bird species projected to undergo the greatest range con- tractions inhabit the temperate areas of the Cape (e.g., the vulner- able Knysna warbler, Bradypterus sylvaticus in South Africa), the Horn of Africa (e.g., the endangered Warsangli linnet, Carduelis johannis in Somalia), East Africa (e.g., the endangered Sharpe’s longclaw, Macronyx sharpie in Kenya), and montane (e.g., the vul- nerable Usambara eagle-owl, Bubo vosseleri in Tanzania) and semi-arid (e.g., the critically endangered Liben lark, Heteromirafra sidamoensis, in Ethiopia) habitats (Huntley et al., 2006). Although Afrotropical birds associated primarily with equatorial and moist tropical forest habitats are expected to experience relatively less change in their distributions (Huntley et al., 2006), species in extensive, ﬂat lowlands, such as the Congo basin, will need to move much greater distances than species in mountainous areas (Loarie et al., 2009). In Southeast Asia, some tropical forest bird species have appar- ently already begun to shift their ranges in response to increased temperatures. Peh (2007) used data from ﬁeld guides to show that 94 common resident species of Southeast Asian forests, such as the little forktail (Enicurus scouleri), brown bush warbler (Bradypterus luteoventris), and russet sparrow (Passer rutilans), shifted the upper, lower or both boundaries of their distributions to higher altitudes from 1971 to 1999. Tropical montane birds in Peru also appear to be shifting ups- lope in response to warming (Forero-Medina et al., 2011). In the Cerros del Sira, the elevational limits of birds from the same spe- cies vary from peak to peak, implying that birds’ range margins are unlikely to be a simple response to temperature. Yet these bird species show a consistent upslope range shifts in response to warming from 1969 to 2010. Nevertheless, their shifts lag behind warming, and this may reﬂect an indirect response to temperature via gradual alteration of their food supplies, habitat, or other inter- actions (see Section 5). Ç.H. Sßekerciog ˘lu et al. / Biological Conservation 148 (2012) 1–18 5 Author's personal copy Where ecosystems migrate in response to temperature change, the availability of habitats and resources for bird species may be disrupted as well. Different types of birds will have varying rates of success in coping with these changes. Success may depend on whether birds’ preferred food sources successfully track climate change and shift to these new vegetation zones or, alternatively, how well the bird species adapt to new vegetation and food sources. The important concern for conservation planners is thus not only how to protect tropical birds now, but also how to deter- mine the rate at which birds and associated tropical ecosystems will migrate over time so that future habitats can also be protected. Loarie et al. (2009) calculated an index of the velocity required for ecological communities to keep up with climate change (Fig. 4). Although this velocity is not uniform across habitats and regions, in general terms, 92% of protected areas are likely to become cli- matically unsuitable in a century, especially in grasslands, savan- nas, deserts, and mangroves (Loarie et al., 2009). Nevertheless, an analysis of African Important Bird Areas (IBA) indicates that all but 7–8 priority species’ will retain some of their preferred climatic envelopes in the IBA network, showing the importance of carefully designed protected area networks (Hole et al., 2009). Protected areas will remain vital, but will need to be enlarged based on future range shift projections. Under climate change, protected area planning must consider not only the current habitat needs of a given species or community, but also the areas that could accommodate future needs as temperatures warm. Ideally, habitat corridors should be used to provide high connectivity between protected areas, but this will require better integration of human-dominated landscapes into conservation schemes. Equally important, protected areas must assess potential barriers to migration, both natural – rivers, oceans, and unsuitable soils – and human-made, including settlements, farmlands, and coastal fortiﬁcations. The problem of extensive protected areas losing bird populations due to climate change (Mac Nally et al., 2009) makes it essential to integrate human-dominated landscapes into conservation areas. 2.9. Manakins: a case study The family Pipridae (manakins) is endemic to the Neotropical region. The roughly 45 species in this family are limited to various forest habitats and nearby second growth. Ranging from lowlands to montane forest, manakins prefer relatively humid conditions, even in drier areas, where they are limited to gallery forest (Snow, 2004). Because these species are restricted to Neotropical forest habitats, consist of dozens of species with varied geographic distri- butions and ecological preferences, and have wide-ranging eleva- tional distributions, manakins provide an ideal opportunity to model climate change effects on the distribution of a tropical bird family. Anciaes and Peterson (2009) used ecological niche model- ing (Peterson et al., 2001) to model manakins’ ecological niches, based on these birds’ present distributions and climatic prefer- ences. They then combined these models with climatic projections for the mid-21st century. The results indicate that manakin species limited to the lowland habitats of the Amazon basin and cerrado (e.g. the helmeted manakin, Antilophia galeata) will be the most af- fected. That is, these species would need to move relatively greater distances to track their environmental niches. These species are ex- pected to lose 80% of their habitable area; moreover 20% of the cer- rado manakin species are expected to go extinct. In other ecoregions dominated by mountains, predicted loss of potential area (16–50%) and expected extinctions (0–5%) are much lower. This demonstrates the importance of topographic diversity in buf- fering against forced range shifts due to climate change. The researchers also predicted that manakin distributions will become more fragmented, highlighting the conservation challenge climate change will pose for many tropical bird groups. 3. Evolution and adaptation: slow lives in a fast-paced new world This section focuses on the aspects of tropical bird species’ life histories and ecologies that may affect their capacity to adapt to Fig. 4. The velocity of temperature change globally. (a) Temporal gradients calculated from 2000–2100 across three emissions scenarios (A2, A1B and B1). (b) Temporal gradients calculated from 2000–2050 and 2050–2100 across three emissions scenarios. Trends plotted here are the average of the global land surface. (c) A global map of climate velocity calculated using the 2050–2100 Special Report on Emissions Scenarios (SRES) A1B emissions scenario temporal gradient. This is the instantaneous local velocity along Earth’s surface needed to maintain constant temperatures at a location, and has a global mean of 0.42 km year ÿ1 . For example, in a dark red area, vegetation would need to shift 10 km year ÿ1 to keep up with climate change. Reprinted with permission from Loarie et al. (2009) The velocity of climate change. Nature 462, 1052–1055. 6Ç.H. Sßekerciog ˘lu et al. / Biological Conservation 148 (2012) 1–18 Author's personal copy climate change. Climate change also has evolutionary conse- quences (Bonaccorso et al., 2006). For some species, adaptive re- sponses such as phenotypic plasticity, learning, and maternal effects, along with migration rates, are unlikely to be sufﬁcient to keep pace with climate change, and the rate of microevolution will be the primary determinant of their ability to adapt to climate change (Visser, 2008). Yet most vertebrates will be unable to evolve rapidly enough to adapt to anthropogenic climate change, exacerbated by extensive habitat loss (Njabo and Sorenson, 2009); bird species will be lost at a far higher rate than the rate of the evolution of new species. On actual and ecological islands, geographic isolation and long- term environmental stability are among the features that promote endemism and speciation, yet these same features make island species especially vulnerable to environmental change (Fordham and Brook, 2010). Tropical mountain areas, for example, have been the centers of speciation and endemism due to their isolation (Voelker et al., 2010) and long-term habitat stability (Fjeldsa and Lovett, 1997; Graham et al., 2006). In Africa, Pliocene climate change has driven the speciation of African forest birds like the Cameroon mountain greenbul (Andropadus montanus) by causing lowland forest retraction and rapid isolation of montane forests (Njabo and Sorenson, 2009; Voelker et al., 2010). Ongoing climate change will further isolate tropical montane forests. However, species’ ecological niches are unlikely to evolve sub- stantially during the decadal time-scales over which climate change is expected to take place (see references in Anciaes and Pet- erson, 2009), especially for organisms with long generation times (e.g. seabirds, parrots, cassowaries). Compared to birds in temper- ate regions, many tropical bird species experience less seasonality and more stable temperature and humidity regimes. These condi- tions favor birds with ‘‘slower’’ lives, that is, those with ‘‘k-se- lected’’ life histories characterized by smaller clutch sizes (Jetz et al., 2008a), lower productivity, and longer life spans (Wiersma et al., 2007). Consequently, tropical bird species with less demo- graphic ﬂexibility than their temperate counterparts are unlikely to evolve as quickly in response to rapid climatic change. More- over, recent research suggests that high-elevation birds have life- history strategies similar to those of low-latitude birds (Tieleman, 2009). This raises further concern about tropical high-elevation species with particularly slow life histories (see above). Not only are high-elevation birds particularly susceptible to climate change, but most high-elevation endemic bird species are found in the tropics. As long-lived homeotherms, many tropical birds’ population growth rates should be less affected by climate change induced variability in their demographic rates (e.g. survival, reproduction, or growth) than those of short-lived species like insects (Morris et al., 2008). Furthermore, research has shown that tropical popu- lations, through their long-term persistence during periods of cli- mate change, have accumulated more genetic variability relative to populations in more temperate areas (and likely at higher eleva- tions in the tropics). Populations of the latter groups have been fre- quently eliminated during colder periods, or have gone through more population bottlenecks, and thus possess reduced genetic variability (Hewitt, 1996). Although tropical birds are longer-lived, on average, than their temperate relatives (Wiersma et al., 2007), the advantage of longer lifespans is likely to be negated by other factors that make tropical birds more vulnerable, such as smaller clutch sizes (Jetz et al., 2008a), more sedentary habits (Sßekerciog ˘lu, 2007), and lower tol- erance of climatic variability (Seavy, 2006; Weathers, 1997). Not all effects of climate change are negative, and changes in temperature and precipitation regimes will beneﬁt some species. How a bird’s life history will respond to climate change may be unexpected and hard to predict, as shown by male northern mockingbirds (Mimus polyglottos). This non-tropical species dem- onstrates more elaborate sexual displays with increased climatic variability (Botero et al., 2009). Warmer temperatures may alter birds’ reproductive strategies, countering some negative demo- graphic effects of climate change, and enabling some species to expand to new areas (Jarvinen, 1994), but this is yet to be demon- strated in the tropics. Conversely, ‘‘r-selected’’ bird species with short generation times, large clutches, multiple broods, and the ability to re-nest after losing an entire clutch, are also more likely to recover from adult, juvenile, and nest mortality caused by extreme weather and other climate change effects (Angert et al., 2011). Generalist species that can use a wide range of habitats and/or feed on differ- ent kinds of food are less threatened with extinction (Sßekerciog ˘lu, 2011). These species are expected to be more likely to adapt to or even beneﬁt from climate change, often at the expense of special- ists. Overall, many traits that reduce birds’ likelihood of extinction to other threats are also likely to prove advantageous in coping with climate change (Wormworth and Sßekerciog ˘lu, 2011). Nevertheless, climate change will not beneﬁt many species. Be- cause individualistic responses are likely, climate change could bring about the formation of novel communities and even lead to community disassembly, especially in diverse tropical communi- ties with a wide range of life histories. 3.1. How physiology and microclimate impact tropical bird species’ ability to adapt Current understanding of interspeciﬁc variation in physiological traits is limited and needs further study. However, we can make some general observations about how these factors will inﬂuence tropical bird species’ ability to adapt to climate change (Bernardo et al., 2007). In comparison to ectotherms, endothermic birds are more likely to be indirectly affected by climate change via its im- pacts on vegetation in their communities, rather than via direct ef- fects on physiology (Aragon et al., 2010). Nevertheless, an increasing number of studies hint at the vital role birds’ physiolog- ical responses to climate change will play (McKechnie, 2008; McNab, 2009). Birds living in hotter and drier habitats (e.g. Somali bee-eater, Merops revoilii) often show physiological adaptations, such as re- duced thermal conductance (Weathers, 1997), lower evaporative water loss (Weathers and Greene, 1998), and higher heat tolerance, exempliﬁed by variable seedeaters (Sporophila aurita;Weathers et al., 2001). Open habitat sunbirds in Uganda (e.g. scarlet-chested Sunbird, Nectarinia senegalensis) have reduced thermal conduc- tance, better insulation and greater ability to tolerate ﬂuctuating temperatures than do forest sunbirds (Seavy, 2006). Lowland and open-country bird species that have adapted to higher tempera- tures are likely to tolerate temperature increases better than high- land species and species of the forest interior (Weathers, 1997). Furthermore, climate change can favor open-country species’ pen- etration into climatically-compromised forest remnants (Laurance, 2004). One theory is that while birds that are thermal specialists perform at a high level but within a narrow band of body temper- atures, thermal generalists can perform at a low level across a wide range of temperatures and maintain a lower body temperature during heat stress (Boyles et al., 2011). Changes in temperature and humidity will also have indirect ef- fects on avian activity and behavior. If birds avoid sites with unfa- vorable climates, this could reduce important activities such as feeding and breeding displays (Walsberg, 1993). Many tropical for- est species, such as silver-throated tanagers (Tangara icterocephala) in Costa Rica, spend a lot of time in the cool and humid forest interior, but they display and forage in exposed areas, such as song perches and fruiting canopy trees. Intensive radio-tracking Ç.H. Sßekerciog ˘lu et al. / Biological Conservation 148 (2012) 1–18 7 Author's personal copy combined with constant monitoring of habitat temperature and humidity revealed that these birds track temperature and humid- ity differences as small as 0.8 °C and 4.2%, respectively (Sßekerciog ˘lu et al., 2007). Physiological limitations also shape habitat selection. In tropical forests, holes or hollows in trees are critical resources for many birds because they provide safe nesting cavities and microclimatic refugia from higher outside temperatures (Isaac et al., 2008). Cav- ity-nesting behavior has recently been shown to be a critical factor in determining avian clutch size, illustrating the importance of cav- ities (Jetz et al., 2008a). As global temperatures increase, tree hol- lows are expected to become more important to birds than ever (Isaac et al., 2008). However, the large, older trees most likely to have these cavities are often those ﬁrst logged in tropical forests; even in protected forests, dead trees that provide hollows are often collected for ﬁrewood. Increasing scarcity of such older trees, com- bined with temperature-sensitive species’ growing need for tree hollows, suggest that cavity-nesters such as woodpeckers, owls, and parrots will face more competition for the remaining hollows. They may need to compete for these resources not only with other birds, but also with cavity-dwelling mammals (Isaac et al., 2008). In Monteverde, Costa Rica, climate change has already enabled keel-billed toucans (Ramphastos sulfuratus), cavity-nesting nest predators, to expand their range into the highlands, where they now compete with the montane forest specialist resplendent quet- zals (Pharomachrus mocinno) for nest holes, as well as preying on quetzal nests (Pounds et al., 1999). 3.2. Basal metabolic rate in tropical birds: implications for survival Basal metabolic rate (BMR), the standard measure of the energy cost of maintenance, has been called ‘‘the obligatory cost of living for endotherms’’ (Barcelo et al., 2009). Although knowledge of BMR is critically important to determine birds’ physiological tolerance to climate change, data on BMR and how it varies among tropical birds is limited. BMR is not a ﬁxed, taxon-speciﬁc trait, but has high phenotypic ﬂexibility (McKechnie, 2008). Compared to ectotherms, birds have more physiological ﬂexibility to respond to temperature changes, but the degree of ﬂexibility also varies greatly among bird species (McKechnie, 2008). BMR is especially ﬂexible in migratory birds (McNab, 2009), and this fact suggests that sedentary tropical birds that live in habitats with low climatic variability are likely to have less ﬂexible BMRs. This inference is supported by an analysis of 71 bird species’ re- sponses to the 2003–2004 heat wave in France (Jiguet et al., 2006). Whereas bird species with the widest thermal range (e.g. carrion crow, Corvus corone) were least affected, birds with the nar- rowest thermal range (e.g. rook, Corvus frugilegus) suffered signiﬁ- cant population declines (Jiguet et al., 2006). The study concluded that a bird species’ thermal range is a reliable predictor of its resil- ience to extreme temperatures. This suggests that thousands of tropical forest bird species that currently experience limited tem- perature variation will be among the most susceptible birds to the physiological effects of warming climates and heat waves. Sim- ilar studies are needed in the tropics. Where the frequency of such heat waves increases, selection pressure will mount and will favor birds that can cope, with thermal generalists likely having an advantage (Boyles et al., 2011). Birds of lower trophic levels, such as frugivores and granivores, tend to have higher BMRs than those at higher trophic levels, such as insectivores (Sabat et al., 2009). Migratory bird species, which experience a wider range of temperatures, also have higher BMRs (McNab, 2009). On the other hand, non-passerines, ﬂightless birds, island birds, and tropical birds tend to have lower BMRs (McNab, 2009; Wiersma et al., 2007). Because higher BMR enables the use of a wider range of thermal environments, increases dispersal ability, and improves adaptability to climate change (Bernardo et al., 2007), birds with lower BMR (e.g., dusky antbird, Cercomacra tyrannina or wedge-billed woodcreeper, Glyphorhynchus spirurus) are at a disadvantage. Most studies of birds’ responses to climate change focus on migratory, mainland passerines of temperate hab- itats. This limited focus suggests that our understanding of birds’ metabolic capacity to adapt to climate change could be overly opti- mistic and unrealistic for most of the world’s sedentary, tropical bird species. The speed and magnitude of a bird’s BMR response may also de- pend on the prevailing temperature of its environment (McKech- nie, 2008). Tropical montane birds that experience lower temperatures (e.g. Papuan mountain-pigeon, Gymnophaps albertis- ii) are likely to show slower responses to future climate change than lowland species. Yet, BMR responses may be critical: even risk-taking and predator avoidance behavior have been shown to be inﬂuenced by BMR (Moller, 2009). BMR variability’s importance as a shaper of birds’ responses to climate change demonstrates why studies of tropical birds’ physiological responses to climate change constitute an urgent research priority. 4. Role of mobility and migration Due to their high mobility, birds are better able to disperse in response to climate change than many other organisms. However, even seemingly rapid distribution shifts may not be sufﬁcient to track climate change (Devictor et al., 2008). Most tropical bird spe- cies and their habitats will not be able to shift fast enough or far enough to track their preferred climate envelopes, particularly in ﬂat, lowland areas (Loarie et al., 2009). Long-distance migratory bird species that have high mobility are expected to suffer fewer extinctions from climate change than sed- entary species (Sßekerciog ˘lu et al., 2008). Higher mobility provides migratory birds with a higher capacity to deal with global change than sedentary (non-migratory) birds. Such sedentary species are already 2.6 times more threatened with extinction than are long- distance migratory bird species (Sßekerciog ˘lu, 2007). Long-distance migratory birds comprise less than a ﬁfth of all the bird species (Sßekerciog ˘lu, 2007), so if non-migratory species prove to be rela- tively more threatened by climate change (Cox, 2010), this will af- fect most of the world’s bird species. Based on 60 different scenarios to estimate bird extinctions that will result from a combination of climate change and habitat loss by the year 2100, Sßekerciog ˘lu et al. (2008) showed that sedentary birds are ﬁve times more likely to go extinct in the 21st century than are long-distance migrants. However, some migratory bird species are also highly vulnera- ble to climate change. Many migratory birds spend most of the year on their wintering grounds in the tropics. Migratory birds that winter in the tropics have their own unique challenges, as they are exposed to the multiple effects of climate change on their breeding grounds, wintering grounds, and during their migrations (Ahola et al., 2007; Both et al., 2006; Huntley et al., 2006). Climate change may result in range reductions at both ends of the journeys of some migratory species such as lesser whitethroat (Sylvia curruca) and garden warbler (Sylvia borin) (Doswald et al., 2009). Climate change could also render key stopover sites unsuitable, and extend the overall migratory journey of some birds (Huntley et al., 2006). Breeding bird surveys showed that while sedentary bird species and short-distance migrants in Denmark increased since 1974, numbers of long-distance trans-Saharan migrants declined 1.3% per year (Heldbjerg and Fox, 2008). An estimated 2.1 billion birds migrate every year between Eur- ope and Africa alone (Hahn et al., 2009). Shifts and reductions in the wintering ranges of migratory birds may have impacts on trop- ical bird communities as well. Barbet-Massin et al. (2009) project that by 2100, climate change could cause the ranges of 37 of 64 8Ç.H. Sßekerciog ˘lu et al. / Biological Conservation 148 (2012) 1–18 Author's personal copy trans-Saharan migrants (e.g. collared ﬂycatcher, Ficedula albicollis and thrush nightingale, Luscinia luscinia) to shrink, as well as shift by an average 500 km. This could result in major decreases in the richness of bird communities in Africa (Barbet-Massin et al., 2009). If migratory birds experience increasingly severe food shortages on their wintering grounds due to reduced rainfall, this could affect non-breeding performance and inﬂuence their time of departure for their breeding grounds (Studds and Marra, 2007). Changes in tropical wintering habitats also create a disadvantage for migrants’ subsequent performance on their breeding grounds. Female Amer- ican redstarts (Setophaga ruticilla) wintering in high-quality habitat produce more young and ﬂedge offspring weeks earlier than females from poor-quality wintering habitat (Norris et al., 2004). Some migratory birds that are unable to synchronize their migra- tory timing with climate change driven shifts in phenology already demonstrate negative consequences (Ahola et al., 2007; Both et al., 2006). Birds already adapted to environments with unpredictable climates are also likely to better tolerate climate change (Canale et al., 2010). This includes nomadic birds that can move large distances when faced with droughts, ﬂoods, and other extreme weather events. 5. Interspeciﬁc interactions and indirect effects Most models of climate change effects on future species distri- butions do not take into consideration interactions between spe- cies because data regarding such interactions are limited. However, changes in biotic associations can be as important as changes in temperature and precipitation, if not more so (Dunn et al., 2009; Jankowski et al., 2010). Preston et al. (2008) showed that including biotic associations in climate change models reduced habitat availability for endangered California plant, butterﬂy, and bird species by 68–100%, as opposed to a climate-only model. The potential habitat of the threatened coastal California gnatcatcher (Polioptila californica californica), a habitat specialist restricted to semi-arid coastal scrublands in California and Mexico, would be greatly reduced under a warmer climate, compared to models that considered climate only, without accounting for this kind of biotic factor (Preston et al., 2008). They indicated that incorporating biotic interactions in climate models is especially important for habitat specialists and species strongly dependent on other species. Such traits typify tropical bird commu- nities. Between-species interactions, mostly unknown to ecologists, will inﬂuence how climate change affects tropical birds. Indirect effects of climate change that act via interspeciﬁc inter- actions have been little studied, but can be surprising and substan- tial. The insights garnered from ﬁndings of species-poor temperate studies do not bode well for tropical bird communities with more species, more interactions, and more possibilities for the interac- tions to go wrong. Climate-induced changes in the temporal parti- tioning of the breeding period can lead to changes in interspeciﬁc competition that have fatal consequences (Ahola et al., 2007). For example, the closer pied ﬂycatchers breed in time to their seden- tary competitor, the great tit (Parus major), the more likely the ﬂy- catchers are to attempt to take over tit nests (Ahola et al., 2007). These attempts can be fatal for ﬂycatchers. Since climate change affects breeding phenology, it could alter the balance of these com- petitive interactions. Similarly, in the tropical cloud forests of Monteverde, Costa Rica, increased temperatures caused a reduction in dry season mist frequency and in the lifting of the cloud base (Pounds et al., 1999). This, in turn, has led to some lowland bird species expanding their distributions upwards. In the same region, Jankowski et al. (2010) showed that interspeciﬁc aggression was a critical factor in con- straining the elevational ranges of forest songbirds. The high eleva- tion specialist slaty-backed nightingale-thrush (Catharus fuscater) was the most submissive of the species tested. This indicates that the slaty-backed nightingale-thrush is likely to lose ground to the more aggressive, lower elevation black-headed nightingale- thrush (Catharus mexicanus) if the latter species expands to higher elevations in response to the warming temperatures in the region (Jankowski et al., 2010). An estimated one third of threatened trop- ical mountain species have ranges that border with congeners that are widespread, lower-elevation species (Jankowski et al., 2010). One hypothesis holds that climate warming could permit lowland tropical species, if they are relatively aggressive and therefore dominate their upland congeners, to expand upslope, forcing sub- ordinate higher-elevation species to retreat upslope in their shrinking mountaintop ranges (Jankowski et al., 2010). However, if a high-elevation species is dominant it may hold the upslope shifts of competitors in check even as climates warm. Novel inter-species interactions due to climate change are not limited to birds. One of the most fascinating and unexpected exam- ples of negative climate change impacts on songbirds has been caused by edible dormice (Glis glis) in the Czech Republic (Adamik and Kral, 2008). With increasing spring temperatures, the cavity- nesting dormice are emerging earlier from winter hibernation. However, only one of four cavity-nesting bird species in the region advanced its breeding dates. This combination has led to high brood losses caused by intensiﬁed nest predation by dormice, whose populations have increased due to favorable weather com- bined with good seed mast years. As Adamik and Kral (2008) point out, ‘‘changes in climate might affect organisms at various trophic levels with often unexpected outcomes. . . [and] ...species most at risk are those at different trophic levels that do not shift at the same rate or in the same direction as their food resources, preda- tors or competitors’’. Populations of forest snakes, which are major predators of tropical forest birds, nestlings and eggs, may increase to the detriment of bird populations; however, this relationship has not yet been explored by ecologists. Effects of climate change on tropical seabirds have received lit- tle attention, but changes in sea surface temperatures can reduce marine prey availability for seabirds (Becker et al., 2007; Le Bohec et al., 2008; Watanuki et al., 2009). Many seabird species have a critical sea surface temperature threshold, above which (as often is the case during El Niño years) the lack of prey leads to unsustain- able chick mortality (Boersma, 1998; Erwin and Congdon, 2007). In addition, age and sex-related variation in climatic inﬂuence on demographic parameters of tropical seabirds (Oro et al., 2010) can lead to different effects of climate change on different ages and sexes of the same species. Reduced prey directly affects sea- bird productivity (Cury et al., 2011), but it can also inﬂuence impoverished island ecosystems, where seabird droppings (guano) provide critical nutrient inputs to these ecosystems (Croll et al., 2005; Sßekerciog ˘lu, 2006b). An interesting example of climate change-induced interactions affecting a tropical bird community comes from seabird nesting islands near the Great Barrier Reef of Australia. A decrease in seabird prey due to an increase in sea-sur- face temperatures has also meant a reduction in seabirds, in their guano, and in the resulting nutrient input for plants on seabird nesting islands (Greenslade, 2008). With fewer nutrients, native Pisonia trees become more susceptible to outbreaks of a sap-feed- ing herbivore and its attendant ant (Greenslade, 2008). In turn, the loss of Pisonia trees reduces important nesting sites for seabirds like black noddies (Anous minutus) and wedge-tailed shearwaters (Pufﬁnus paciﬁcus), illustrating the complicated web of interactions through which climate change effects reverberate. 5.1. Ecosystem functions and services As the above example illustrates, tropical bird species not only interact with one another, but also provide key ecosystem functions Ç.H. Sßekerciog ˘lu et al. / Biological Conservation 148 (2012) 1–18 9 Author's personal copy and services by interacting with other organisms such as seed dis- persers, pollinators, predators, nutrient dispersers, scavengers, and ecosystem engineers (Sßekerciog ˘lu, 2006a; Wenny et al., 2011). Avian ecological functions and ecosystem services are important in many tropical communities, but the inﬂuence of climate change on these services is little understood. Bird pollination is more important in the tropics than in the temperate zone, except in Australia, where bird pollination peaks in the temperate regions (Ford, 1985). Although bird pollination has often been considered relatively unimportant in comparison to insect pollination, climate change may increase its importance. This is exempliﬁed by some Caribbean islands, where bird pollination increased with higher rainfall, while insect pollination decreased (Gonzalez et al., 2009). Ecosystem functions and services become even more important with the increasing variability climate change brings. Mazia et al. (2009) showed that during the wet year of an ENSO cycle, exclud- ing insectivorous birds such as thorn-tailed rayaditos (Aphrastura spinicauda) and white-crested elaenias (Elaenia albiceps) from tree saplings in an Argentinean Nothofagus forest resulted in twice as much leaf damage by insects as was observed during a drought year. These results indicate that large-scale climatic events can inﬂuence the strength of trophic cascades, but our understanding of such variable effects on ecosystem function, especially in the tropics, is limited (Van Bael et al., 2004). 6. Destructive synergies: climate change exacerbates other environmental stressors Climate change is expected to physiologically stress organisms and force species and entire communities to shift their distributions. Yet climate change will also affect biodiversity by synergistically interacting with, and often exacerbating, other environmental stressors such as habitat loss, emerging diseases, invasive species, hunting, or pollution (Brook et al., 2008; Laurance and Useche, 2009; Reino et al., 2009). However, these synergies are often over- looked in climate change research. One review found that about half of the papers in climate change literature considered climate change separately from other threatening processes (Felton et al., 2009). Tropical birds seem to be particularly vulnerable to the synergisms between climate change and hunting, and between climate change and habitat loss in the form of agriculture (Laurance and Useche, 2009). Nevertheless, remaining uncertainties about temperature and precipitation projections for the tropics (Vera et al., 2006) and the responses of tropical forests to changes in CO 2 , temperature, and rainfall (Feeley et al., 2007; Laurance and Useche, 2009; Phillips et al., 1998) limit our ability to predict future synergies. 6.1. Habitat loss Extensive habitat loss in the tropics will continue to interact with and exacerbate the effects of climate change on tropical birds, especially endemic and range-restricted species (Jetz et al., 2007; Sßekerciog ˘lu et al., 2008). Sßekerciog ˘lu et al. (2008) quantiﬁed the relative impact of habitat loss on bird extinctions caused by cli- mate change by combining IPCC, 2007 climate change scenarios (IPCC, 2007) with Millennium Ecosystem Assessment habitat loss scenarios (MA, 2005). In the ‘‘worst case’’ surface warming esti- mate of 6.4 °C by 2100, (which may yet be an underestimate (Stainforth et al., 2005)), Sßekerciog ˘lu et al. (2008) estimated that the worst case habitat loss estimates in the ‘‘Order from Strength’’ scenario (MA, 2005) could result in over 2500 land bird extinctions and could increase bird extinctions from climate change by about 50% when compared with the best-case estimates from the ‘‘Adap- tive Mosaic’’ scenario (Fig. 5). Furthermore, the authors showed the sensitivity of bird extinctions to the combined effects of climate change and habitat loss to be quadratic. This means that extinctions increase faster than would be expected from a one- to-one relationship with surface warming. With increasing amounts of baseline warming and habitat loss, each additional °C of surface warming is expected to result in more bird extinctions, ranging from approximately 100 to 500 additional extinctions (Sßekerciog ˘lu et al., 2008). The number of extinctions rapidly in- crease past 1.8 °C of surface warming, as do the additional extinc- tions from the climate change-habitat loss interaction effect. This emphasizes the critical importance of restraining global warming to less than 2 °C by 2100. However, an analysis of the most recent emissions pledges during the December 2011 international cli- mate-change negotiations in Durban indicates that the world is headed for 3.5 °C of warming by the year 2100 (Tollefson, 2011). Warming of 3.5 °C could result in 600–900 of nearly 8500 land bird species worldwide being committed to extinction (Sßekerciog ˘lu et al., 2008;Fig. 5), in the absence of any conservation action. 87% of all bird species and 89% of all land bird species occur in the tropics (Çag ˘an H. Sßekerciog ˘lu, unpublished data). Vegetation also displays a non-linear sensitivity to lapse rate. Lapse rates are lower in the tropics, especially in more humid areas, and this implies that tropical forests will be forced to shift further than temperate forests for every °C of surface warming (Sßekerciog ˘lu et al., 2008). However, most models of climate change effects on community shifts are based on data from temperate ecosystems (e.g. Chen et al., 2011), where lapse rates tend to be higher. 6.2. Hunting Other factors, such as hunting, also interact with climate change and exacerbate its effects on tropical bird populations. Traill et al. (2009, 2010) developed one of the few spatially explicit population viability models for a tropical waterfowl species, the magpie goose (Anseranas semipalmata), to simulate population responses to the synergy of hunting, climate change, and increased diseaseprevalence due to climate change. Without hunting, the simulated disease outbreaks (Traill et al., 2009) or wetland loss due to sea level rise 0 500 1000 1500 2000 2500 Millennium Ecosystem Assessment Scenarios Surface warming estimates 1.1°C 1.8°C 2.8°C 4.0°C 6.4°C Estimated landbrid extinctions by 2100 AM TG GO OS AM TG GO OS AM TG GO OS AM TG GO OS AM TG GO OS Fig. 5. Number of world landbird species projected to be committed to extinction by 2100 on the basis of the estimates of various surface-warming estimates (IPCC, 2007), three possible shifts in lower elevational limit, and Millennium Assessment habitat-change scenarios (MA, 2005; AM, adaptive mosaic; GO, global orchestra- tion; OS, order from strength; TG, technogarden). Bars show the results of an intermediate amount of elevational shift, where lower limits of 50% of lowland (6500 m) bird species are assumed to move up in response to surface warming. ‘‘Error bars’’ indicate best-case (0% move up) or worst-case (100% move up) climate warming scenarios. Reprinted with permission from Sßekerciog ˘lu et al. (2008). Climate change, elevational range shifts, and bird extinctions. Conservation Biology 22, 140–150. 10 Ç.H. Sßekerciog ˘lu et al. / Biological Conservation 148 (2012) 1–18 Author's personal copy (Traill et al., 2010), even when they increased due to climate change, rarely threatened meta-population viability, and only when there was high mortality and regular disease outbreaks. With current hunt- ing pressure, however, the population response switched from a threshold response to a linear one, and the threat to meta-population viability from a disease outbreak or wetland loss increased signiﬁ- cantly. It is necessary to consider the synergies of climatechange with various factors simultaneously, rather than in isolation. 6.3. Invasive species While climate change poses a crisis for many specialized tropi- cal bird species, it presents opportunities to other, more invasive species that will expand their ranges into more temperate regions (Reino et al., 2009). The expansion of invasive species will result in new communities and ecological interactions with consequences that are often hard to predict, but are likely to be negative for some species. For example, rose-ringed parakeets (Psittacula krameri), are highly social and could aggressively compete for food and nesting cavities with other birds (Pithon and Dytham, 2002). Further expansion of their distributions in Europe could come at the ex- pense of other native cavity-nesting species (Leech and Crick, 2007). Other tropical and subtropical bird species that are either introduced by people or expand their ranges naturally are becom- ing established in new localities, where native birds now have to compete with them (Bohning-Gaese and Lemoine, 2004). 6.4. Emerging diseases and shifting disease vectors Increases in the prevalence of infectious diseases provide some of the most important examples of a destructive synergy with cli- mate change effects. Changes in temperature, humidity and precip- itation will affect many pathogens, and climate warming is likely to ‘‘...increase pathogen development and survival rates, disease transmission, and host susceptibility. . . [Most] host-parasite sys- tems are predicted to experience more frequent or severe disease impacts with warming’’ (Harvell et al., 2002). Some recent exam- ples from the tropics include the expansion of avian malaria with increasing temperature (Williams, 2010) and climate change (Garamszegi, 2011), Plasmodium (malaria) and Trypanosoma avian blood parasites being linked to temperature and rainfall (Sehgal et al., 2011), and a rise in coral diseases (Harvell et al., 2002). An expansion of malaria-carrying mosquitoes into Hawaiian highland forests could threaten many Hawaiian endemic bird species (e.g. the rare and declining akiapolaau, Hemignathus munroi, endemic to the island of Hawaii). Native birds of the Hawaiian Islands had no experience with malaria or mosquitoes before they were intro- duced to the islands in the nineteenth century (Freed et al., 2005). With increasing warming, the elevational distributions of the 13 °C isotherm (above which malaria does not occur) and the 17 °C iso- therm (below which malaria is year-round and high-risk) are ex- pected to move upslope (Atkinson and LaPointe, 2009). This is expected to greatly reduce the disease-free refugia in high-eleva- tion forest habitat (by up to 96%), where malaria is low-risk or is found only seasonally (Atkinson and LaPointe, 2009). As avian ma- laria is found throughout the world, similar climate-related in- creases in disease prevalence among tropical birds (such as montane endemics) will be widespread, and will be most threaten- ing to species with little or no evolutionary experience of various parasites. However, there are few long-term studies on the subject. 7. Seasonality and variability The stereotypical view of tropical bird life history has been that of a lack of seasonality compared to that of temperate birds. However, detailed and long-term studies are revealing that many species, such as Panama’s spotted antbirds (Hylophylax naevioides), experience seasonality due to wet-dry season cycles (Tye, 1992; Wikelski et al., 2003, 2000). One of the few known examples of tropical birds’ phenological responses to climate variation comes from Cameroon, where individual bird species switch from breed- ing in the wet season in the lowlands to breeding in the dry season in the highlands (e.g. little greenbul, Andropadus virens and African thrush, Turdus pelios). This observation suggests the types of re- sponses possible under climate change (Tye, 1992). In mountains, heavy rainfall, high humidity, and low tempera- tures during the wet season often prevent birds from breeding, including species that are more typical of the drier and hotter low- lands, where they normally prefer to breed in the wet season (Tye, 1992). It is likely that many tropical bird species will shift their breeding periods in response to changes in temperature and rain- fall regimes. If climate change results in a mismatch between a critical reproductive cue such as the photoperiod (Wikelski et al., 2000) and the optimal temperature and rainfall regime for repro- ductive success, population declines may be the result. Changes in the frequency and severity of tropical storms also have impor- tant implications for the ecology and conservation of tropical birds (Boyle et al., 2010). Research on the effects of climate change has almost entirely fo- cused on the changes in average temperature, and to a lesser extent, in rainfall. However, changes in weather events (Reside et al., 2010) and seasonality can be equally important, particularly in the tropics, where seasonality is less pronounced than in the temperate zone and where organisms are adapted to fewer climatic ﬂuctuations and extremes. Nevertheless, some tropical forests may be able to adapt to changes in seasonality better than temperate forests be- cause the relative unpredictability of seasonality in the tropics may have selected for more ﬂexible responses to seasonality (Corlett and LaFrankie, 1998). Although temperatures show relatively little variation in the tropics, rainfall shows some seasonality even in the wettest tropical areas, and many tropical regions experience a distinct dry season that results in periods of low food availability. For birds and other animals, however, increases in rainfall sea- sonality and consequent increases in resource bottlenecks are likely to exacerbate the expected impacts of changes in temperature and precipitation regimes (Williams and Middleton, 2008). This is par- ticularly the case for extended dry periods when birds experience a scarcity of food resources such as nectar, fruit, and insects. As many tropical birds time their breeding with increased resource abun- dance typical of the wet season (e.g. white-throated thrush, Turdus assimilis), longer and less predictable dry seasons, droughts, and sea- sonal asynchrony as a result of climate change can affect the migra- tions and reproductive performance of tropical birds, lead to the mistiming of life history events, and potentially result in population declines (Corlett and LaFrankie, 1998; Sßekerciog ˘lu, 2010b; Williams and Middleton, 2008). Greater climatic seasonality, especially of the dry periods, is thought to be linked to lower bird densities in the bird communities of Australia’s Wet Tropics rainforest (Williams and Middleton, 2008), supporting the hypothesis that more climati- cally-stable areas are more diverse (Pianka, 1966). Long-distance migratory birds wintering in the tropics can also experience disad- vantages, such as reduced body mass prior to migration, due to drier conditions in wintering habitat (Smith et al., 2010). A different challenge faces the Mauritius kestrel, Falco puncta- tus. This formerly critically endangered island endemic breeds later in wetter springs. Senpathi et al. (2011) found that spring rainfall is now 60% more frequent in their study area than it was in 1962, and for each extra day of rainfall, birds delayed breeding by half a day. Later breeding has negative repercussions for Mauritius kestrel nesting success, because it increases the breeding risks associated with climate conditions later in the reproductive season: nests are more likely to be ﬂooded, exposing chicks to hypothermia; and Ç.H. Sßekerciog ˘lu et al. / Biological Conservation 148 (2012) 1–18 11 Author's personal copy adults are more likely to face adverse hunting conditions due to wet weather (Senpathi et al., 2011). Because we have limited understanding of how changes in rain- fall seasonality will effect tropical bird populations and species richness of bird communities, more tropical studies are needed. 7.1. Extreme weather events Global warming, by increasing the amount of energy and humid- ity in the climate system, also increases climatic variability. This is likely to increase the magnitude and frequency of extreme weather events, such as heat waves, droughts, ﬂoods, cold spells, ‘‘once-in- a-century’’ storms and tropical cyclones (IPCC, 2011). Such extreme weather events can be as destructive to plants and bird communi- ties as higher average temperatures and changes in rainfall patterns, if not more so. It may be possible for a bird species to cope with a 2°C change in average temperature, but if that results in an increase in extreme weather events that destroy critical habitat or make for- aging impossible (Boyle et al., 2010), the species can decline to- wards extinction (Martinez-Morales et al., 2009). The balance of evidence points to increases in the numbers of intense tropical cy- clones (though tropical cyclone frequency could decrease overall). This would predominantly affect tropical bird communities, espe- cially species living in coastal and island habitats (Lee et al., 2008; Martinez-Morales et al., 2009; Safford and Jones, 1998), like the Cozumel thrasher (Toxostoma guttatum). Furthermore, habitats damaged by tropical cyclones may be very slow to recover if their regeneration depends on seed dispersal by birds (Hjerpe et al., 2001). At present, few population models account for the adverse effects of more frequent or intense extreme weather events. El Niño and La Niña cycles can have particularly dramatic ef- fects on tropical forest birds, depending on the extent and severity of aseasonal rainfall and droughts that result from these inter-an- nual patterns of climate variation (Jaksic, 2004). Some tropical birds, especially granivores and insectivores, can respond rapidly to the effects of El Niño-driven rainfall changes, including increases in plant and insect productivity. For example, on the Galapagos Is- lands, land birds thrive during El Niño years while seabird breeding success plummets. Long-term studies are needed to understand how these responses affect bird population cycles (Jaksic, 2004). Fires are also extreme climate-related events with major reper- cussions for wild bird populations. Fire frequency and area burned is expected to increase in many world regions, both as a result of climate change and human alteration of habitat. One study of trop- ical savannah species in northern Australia indicated that an in- crease in ﬁre frequency late in the dry season would have a negative effect via decreases in predicted ranges of almost all bird species (98% of those studied) restricted to this habitat (Reside et al., 2012). In Papua New Guinea, a 2007 research expedition also documented the vulnerability to ﬁre of the Papuan harrier (Circus spilothorax), which breeds in damp grassland and ﬂoodplains at the start of the dry season. Two of the ﬁrst nests ever recorded were consumed by ﬁre within ﬁve weeks of their discovery. In re- sponse to the risk of higher ﬁre frequency on Papua New Guinea under climate change, it has been proposed that these harriers be listed as vulnerable (Simmons and Legra, 2009). Tropical forest ﬁres are becoming larger, more frequent and severe, even in forests where they were formerly infrequent (Cochrane, 2003). 8. Discussion Change has been a feature of Earth’s climate throughout time. However, although past climate change has often been of lesser magnitude and speed, it has nevertheless resulted in major upheavals in the planet’s ecosystems and dependent organisms (Huntley et al., 2006). Even in the most rapid past episodes of natural climate change during the transitions between glacial and interglacial periods (Schneider, 1989), when some local tem- peratures rose as much as 8 °C in a few decades (IPCC, 2007), the average global temperature increased by about 5 °C over 5000– 7000 years (Huntley et al., 2006). The current rate of global temperature increase is extremely rapid by comparison – one or two orders of magnitude greater than that observed in the past. The planet’s average temperature is expected to increase by 1.1–6.4 °C this century, according to the Intergovernmental Panel on Climate Change (IPCC, 2007). The potential role of little-known or even unknown feedback loops makes the upper limit hard to predict, and an average temperature increase of up to 11 °C may be possible (Stainforth et al., 2005). Already, most tropical climates are the warmest they have been in the past two million years (Bush, 2002) and ‘‘. . .global climate is thus projected to be at least as warm, by the end of the present century, as it has been at any time during the evolution of most of the world’s present diversity of organisms’’ (Huntley et al., 2006). Some argue that species will simply adapt as they have done during past episodes of climate change. This argument is unrealis- tically optimistic not only because of the large magnitude and high rate of global change, but also because species must now contend with more than 7 billion human beings who consume most of the planet’s resources and eliminate wildlife habitats. Human popula- tion is expected to reach 9 billion by 2050 and this is expected to lead to further land clearing (MA, 2005) and greenhouse gas emis- sions (IPCC, 2007). This will further complicate other species’ abil- ity to carry out range shifts, the response thought to have dominated biodiversity’s reaction to past episodes of climatic change (Huntley et al., 2007). Biodiversity is highest in the tropics, but the numbers of subsistence and smallholder farmers are also the greatest (Hannah et al., 2002). Although these people will be highly exposed to climate change effects, their ability to cope will be limited. Their efforts to adapt will lead to further clearance or degradation of forests and other habitat (Easterling et al., 2007). Although a recent meta-analysis has shown that in areas of greatest warming average latitudinal shifts of species have been generally adequate to track temperature changes (Chen et al., 2011), due to the scarcity of suitable data, only 2 out of 22 studies meta-analyzed were from the tropics (15 of 36 comparisons were from a single UK study), and neither tropical study was on birds. Compared to temperate species that often experience a wide range of temperature on a yearly basis, tropical species, especially those limited to tropical forests with stable climates, are less likely to keep up with rapid climate change. Projected climate change will lead to conditions unprecedented for millions of years, and as a re- sult, bird species’ equator-ward limits (and likely their lower eleva- tion limits) may retreat roughly in equilibrium with climate change, whereas their pole-ward (and higher elevation) limits are likely to lag behind (Huntley et al., 2006). Range expansion typically re- quires the concomitant expansion of bird habitat, which generally entails the range expansion of plants that may be long-lived and slow to disperse. Range expansion of vegetation may be relatively slow, even across suitable terrain not occupied by people. Together, these factors indicate that habitat expansion to newly suitable areas will not take place quickly enough to make up for habitat losses due to climate change, especially for relatively sedentary tropical forest species. Rapid range reductions will result, and equa- torial populations with higher genetic diversity will be among the ﬁrst ones to go (Huntley et al., 2006; Sßekerciog ˘lu et al., 2008). 8.1. Future projections and models Climate-based models of the geographic distributions of species and vegetation are constantly improving, while achieving ﬁner resolution, improved representation of key processes, and more 12 Ç.H. Sßekerciog ˘lu et al. / Biological Conservation 148 (2012) 1–18 Author's personal copy accurate depiction of oceanic circulation (Karnauskas et al., 2012). However, relatively few climatic stations are available in the tropics, and tropical climate models based on limited data can be a source of uncertainty that may affect the outcomes of species distribution models (Soria-Auza et al., 2010). The utility of such models also hinges on good quality species distribution data. This is particularly challenging when it comes to the often poorly-known distributions of tropical species, some of which may be based on a handful of points from specimens collected a century ago. Jetz et al. (2008b) showed that the distributions of hundreds of bird species in rela- tively well-known North America, South Africa, and Australia are overestimates. Critically, the level of overestimation was higher for threatened, range-restricted, and specialized birds – those most vulnerable to global change. Therefore, detailed datasets with good data on absence as well as presence is preferable (Huntley et al., 2006). As a further challenge, many models confound occurrence with the probability of detection. To address this, recently developed occupancy models can use basic presence/absence survey data from citizen science projects like bird atlases, while accounting for prob- ability of detection (Altwegg et al., 2008). However, the kind of detailed data provided by bird atlases usually requires hundreds or thousands of dedicated, disciplined, knowledgeable, and well- trained amateur and professional ornithologists – personnel not available in most tropical countries (see below). In these cases, the data from birdwatchers must be put to better use (Sßekerciog ˘lu, 2002;www.ebird.org;www.worldbirds.org). Another concern is that static climate models may be inade- quate for mapping future ranges. In fact, even dynamic models may be inadequate in predicting species’ ranges, which are also inﬂuenced by ecological processes such as species interactions, adaptation, and ﬂexibility in life history (Schwager et al., 2008). Models need to do a better job in considering slowly-changing pro- cesses and mechanisms (Schwager et al., 2008) and incorporating species’ interactions. Globally, species with restricted distributions are concentrated in the tropics, and many of these species are already threatened with extinction (Stattersﬁeld et al., 1998). In birds, decreasing range size due to habitat loss increases the likelihood of extinction due to climate change (Schwartz et al., 2006). To make matters worse, model ﬁt also declines for species with smaller ranges, resulting in high uncertainty in predicting climate change extinc- tions in these species (Schwartz et al., 2006). Excluding these spe- cies from conservation management plans could result in their extinction. Conversely, mistakenly including species as threatened when they are actually not could lead scarce conservation re- sources to be squandered. Uncertainties like these apply even to well-known bird species of eastern United States (Schwartz et al., 2006), but the problems with predicting climate-change driven extinctions for little-known tropical bird species are much greater. Extensive range shifts and species turnover are expected under climate change. Yet, substantially different model projections can result, depending on both the climate and species distribution mod- els selected (Bellard et al., 2012). Species turnover in response to climate change, along with temperature and precipitation predic- tions, remain subject to large uncertainties (Diniz et al., 2009; Vera et al., 2006). Despite all the uncertainties involved, a recent compar- ison of 130 observed and 188 predicted ecological responses to climate change supported the predictions of high extinction risk (MacLean and Wilson, 2011); the corrected mean extinction proba- bility of 10% for the predictions was actually conservative compared to the mean probability of 14% based on the empirical evidence. 8.2. The need for more tropical research As is generally the case in ecology and conservation, the tem- perate zone has been the focus of most studies of climate change and most modeling exercises on the changes in species distribu- tions. Fewer than 1% of the long-term climate change data sets come from the tropics (Rosenzweig et al., 2008) and far more tropical ornithological research is needed (Harris et al., 2011; Sßekerciog ˘lu, 2012). For example, the above-mentioned global over- view of the shifts in species’ elevational and latitudinal limits caused by climate change that included only Holarctic studies of birds (in Europe and North America; Chen et al., 2011). Even though most birds species are tropical (Tscharntke et al., 2008) and sedentary (Sßekerciog ˘lu, 2007), the lopsided concentration of researchers and long-term datasets in the developed countries of the temperate zone (Rosenzweig et al., 2008) have meant that most of our understanding of climate change impacts on birds is based on the studies of temperate birds that are largely migratory. To comprehensively understand the implications of climate change for avian ecology and bird conservation, many more long-term studies of tropical bird communities are needed (Perry et al., 2011), especially those that consider responses along elevational gradients (e.g. Laurance et al., 2011; Pounds et al., 1999; Shoo et al., 2005a). This necessitates increased funding to establish more long-term, multi-site ﬁeld research projects (Sßekerciog ˘lu, 2012). Confronted with the relative scarcity of ﬁeld studies on climate change, ornithologists have found innovative ways to investigate its effects (albeit mostly in temperate regions). They have analyzed differences in bird distribution data in successive ﬁeld guides (Peh, 2007), probed the notebooks of nineteenth-century amateur natu- ralists (Primack et al., 2009; Willis et al., 2008), and amassed mil- lions of data points collected by experienced birdwatchers who volunteer for citizen science projects such as the US Breeding Bird Survey (Niven et al., 2009), the European Breeding Bird Atlas (Hagemeijer and Blair, 1997), and e-bird (www.ebird.org). How- ever, amateur interest in birds is less prevalent in tropical coun- tries. These nations are largely characterized by developing economies and less educated populations more concerned with survival than with birdwatching. Nevertheless, the appeal of birds is universal, interest in birds is growing in developing, tropical countries (Sßekerciog ˘lu, 2012), and birdwatching can also become a means towards a sustainable livelihood (Sßekerciog ˘lu, 2002). Gi- ven sufﬁcient opportunity and motivation, people in tropical coun- tries are likely to appreciate birds and rapidly learn to identify them (Paaby et al., 1991). Because most tropical households have low income thresholds, limited funds for research and monitoring can go a long way (Sßekerciog ˘lu, 2012). Field guides make bird iden- tiﬁcation accessible to most of the world’s population. The bird- watching tourism market is also global; if people of tropical countries are provided with ornithological training, this can lead to careers that combine bird guiding and scientiﬁc data collection. In this way, locally based, long-term bird monitoring programs in the tropics could combine biodiversity monitoring, environmental education, raising local awareness, community-based conserva- tion, and ecotourism development (Sßekerciog ˘lu, 2012). Such pro- grams can be successful and cost-effective tools for job creation and poverty reduction in many developing countries. 8.3. The value of protected areas for tropical birds: planning for future change We urgently need to understand how climate change will affect the capacity of protected areas to harbor species and communities (Willis et al., 2009). Especially in areas prone to drought, climatic extremes reduce food availability – and consequently, breeding success – and can therefore lead to widespread bird population de- clines even in large reserves (Mac Nally et al., 2009). By contrast, higher, cooler climatic refugia on tropical mountains are dispro- portionately important for restricted range species, and steep mountains, where human activity is limited, are often afforded Ç.H. Sßekerciog ˘lu et al. / Biological Conservation 148 (2012) 1–18 13 Author's personal copy protection from human disturbance. For example, in the Wet Tropics of Queensland, the coolest part of the rainforest harbors 45% of endemic species (Shoo et al., 2011). Such climatically diverse tropical montane areas have buffered cold-adapted species from extinction during past interglacial periods of unusually warm global temperatures (Ohlemuller et al., 2008). However, climate change will disproportionately affect the narrow climatic zones that characterize these centers of species rarity. This will jeopar- dize many restricted-range species (Ohlemuller et al., 2008), such as the Mt. Apo sunbird (Aethopyga boltoni) in the Philippines or the regal sunbird (Nectarinia regia) in East Africa (Fig. 3). We must design networks of protected areas with climate change in mind because this will be critical for conservation (Shoo et al., 2010). The Important Bird Area (IBA) network of Africa in- cludes 1230 sites essential for maintaining populations of priority species (Hole et al., 2009). Climate-induced shifts in the distribu- tions of the breeding birds of sub-Saharan Africa are expected to result in 42% of IBAs showing >50% species turnover (Hole et al., 2009). However, only 7 or 8 priority species’ preferred climatic envelopes are projected to be entirely lost from the IBA network, and about 90% of priority species should retain suitable climatic space somewhere. Nonetheless, sophisticated conservation plans will be fruitless unless they are applied effectively in collaboration with local people and decision-makers. Equally, these plans will rely on improvements to landscape connectivity and efforts that make the human-dominated landscapes surrounding protected areas more hospitable to bird populations. 8.4. Research and management Our limited knowledge of climate change impacts hinders our ability to measure, predict, and prepare for the growing effects of climate change on tropical ecosystems and bird populations (Laurance et al., 2011). Research is urgently needed in the follow- ing four main areas: species ecology, climate change impacts on species, range shifts, and management action (Miller-Rushing et al., 2010). To create effective conservation management plans, it is critical to collect basic ecological data, such as range size, habitat needs, important interactions, evolutionary biology, and climate sensitiv- ity. This data collection must be prioritized and funded (Lankau et al., 2011; Sßekerciog ˘lu, 2012). In addition, models that predict cli- mate change impacts must be improved. More accurate models are particularly important to project where different vegetation types and their dependent organisms will move. This will help identify, protect and (in some cases) allow for the purchase of areas where species will shift, along with the habitat corridors that may enable them to do so. While conservation ecologists should increase their research on tropical birds, conservation practitioners should use an adaptive management framework to mitigate climate change effects on tropical bird communities. Adaptive management will be critical to reduce tropical bird extinctions from climate change. Managers need to publish their ﬁndings regularly, so that the lessons learned can be shared and used to improve conservation efforts. This is critical to the success of the adaptive management framework, comprising ‘‘the identiﬁcation of management questions and goals, implementing management practices, testing the effectiveness of the practices, and re-evaluating and revising the practices’’ (Mill- er-Rushing et al., 2010). The ﬁrst step is to identify and monitor the populations and species at greatest risk from climate change. Long-term manage- ment of the designated populations, species, and their habitats must then follow, including new and expanded protected areas, and corridors based on projections of their ranges. Where possible and cost-effective, restoring lands degraded by climate change (or other factors) in essential localities will bolster tropical bird popu- lations and will buy time for birds to shift to more suitable areas. Finally, for some highly sedentary tropical bird species threatened with extinction, assisted migration may be necessary (Hewitt et al., 2011). This case for capture and relocation of individuals to more suitable localities may be particularly applicable to many tropical forest understory species, birds on low tropical mountains, low-ly- ing island specialists, and sedentary birds whose current and fu- ture ranges are not connected. Nevertheless, such efforts will be temporary ﬁxes if we fail to achieve immediate societal change to reduce consumption, to con- trol the emissions of greenhouse gases, and to stop climate change, in combination with having effective conservation areas that enable organisms to shift in response to climate change that is already happening. Otherwise, we face the prospect of an out- of-control climate that will not only lead to enormous human suf- fering, but will also trigger the extinction of countless organisms, among which tropical birds will be but a fraction of the total. Acknowledgements We are grateful to Sean Anderson, Elizabeth Platt, Jason Socci, Navjot S. 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Study of avifaunal diversity is an essential ecological tool which acts as an important indicator to evaluate different habitats both qualitatively and quantitatively (Bilgrami, 1995). Unfortunately global diversity of birds is decreasing incessantly primarily due to anthropogenic disturbances (Rapoport, 1993) and climate change (Chen et al., 2011; Sekercioglu et al., 2012). No surprise that IUCN Red List of endangered birds has already recognized 1226 bird species as threatened globally and India with 88 threatened bird species is ranked at seventh position (BirdLife International 2010). ... Article Full-text available A rapid avifaunal diversity assessment was carried out at three different locations of north Bengal viz. Gorumara National Park (GNP), Buxa Tiger Reserve (BTR) (Jayanti/Jainty range) and Rasik Beel Wetland Complex (RBWC) during 2 nd No-vember and 14 th November 2008. A total of 117 bird species belonging to 42 families were recorded during the present short span study. The highest bird diversity was recorded in GNP with 87 bird species, followed by RBWC (75) and BTR (68). The transition zones between GNP and BTR, BTR and RBWC and GNP and RBWC were represented by 51, 41 and 57 common bird species, respectively. A total of 36 bird species were recorded in all three study sites. This diverse distributi on of bird species was reflected in the study of diversity indices where the highest Shannon–Wiener diversity index score of 3.86 was recorded from GNP followed by RBWC (3.64) and BTR (2.84). The similar trend was also observed for Simpson's Dominance Index, Pielou's Evenness Index and Margalef's Richness Index. Consequently in the dendrogram analysis, we found that GNP and RBWC were much closer to each other while BTR remained distantly located form this cluster. The present study recorded two birds viz. Black-naped oriole (Oriolus chinensis) and Marshall's iora (Aegithina nigrolutea) pre-viously not reported from the present study location. Like other protected areas of the country the present study location is also facing conservation challenges and more intensive studies will certainly reveal the impact of anthropogenic alteration of the habitats in and around the present study location along with the enrichment of knowledge for the avifaunal diversity. Article Full-text available An analysis of the elevational distributions of Southeast Asian birds over a 28-year period provides evidence for a potential upward shift for 94 common resident species. These species might have shifted their lower, upper, or both lower and upper boundaries toward a higher elevation in response to climate warming. These upward shifts occurred regardless of habitat specificity, further implicating climate warming, in addition to habitat loss, as a potentially important factor affecting the already imperiled biotas of Southeast Asia. Chapter Full-text available W.E.Easterling, P.K. Aggarwal, P. Batima, K.M. Brander, L. Erda, S.M. Howden, A. Kirilenko, J. Morton, J.-F. Soussana, J. Schmidhuber and F.N. Tubiello, 2007: Food, fibre and forest products. Climate Change 2007: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, M.L. Parry, O.F. Canziani, J.P. Palutikof, P.J. van der Linden,C.E. Hanson, Eds., Cambridge University Press, Cambridge, UK, 273-313. Article Full-text available The Galápagos Penguin (Spheniscus mendiculus) population probably has always been small and largely restricted to the islands of Fernandina and Isabela. Counts suggest the current population of Galápagos Penguins is likely between 4,250 and 8,500, half of what it was in the early 1970s. Population size has varied and declined probably because of substantial changes in oceanic conditions. Body condition as evidenced by weight is enhanced during cold surface water conditions, La Niña, and deteriorates when surface waters are warmed, El Niño, and under the most severe conditions, penguins starve. Analysis of a long-term data set from counts of the population suggests that the population has fluctuated, dropping precipitously after the 1982-1983 El Niño and has since then been recovering very slowly. This parallels the overall warming in the Pacific during the last 20 years associated with the more frequent El Niño and less frequent La Niña events. These trends suggest that long-term global climate warming is likely to threaten the Galápagos Penguin population particularly because the population is small and its distribution restricted. New threats from climatic warming and increasing human perturbations such as fishing, inadvertent discharge of petroleum products, and transport of potential predators and pathogens to islands increase the risk of extinction. Article Bridled Titmice (Baeolophus wollweberi) and Juniper Titmice (B. ridgwayi) occur sympatrically in southeastern Arizona, with Bridled Titmice preferring habitats that are more heavily vegetated, moister, and cooler than those occupied by Juniper Titmice. To assess whether these differences in habitat preference have physiological correlates, we measured the oxygen consumption, evaporative water loss, and body temperature of post-breeding titmice at ambient temperatures between 24-44°C. Bridled Titmice were less tolerant of heat than Juniper Titmice and had significantly higher rates of metabolic heat production and evaporative water loss, but not body temperature, at ambient temperatures above 40°C. These differences were entirely attributable to the Bridled Titmouse's smaller body size (10 versus 15 g), and the differences vanished when rates were expressed per unit metabolic mass (mass raised to either the 2/3 or 3/4 power). Within the thermoneutral zone, the rate of evaporative water loss (EWL) was significantly lower in Juniper Titmice than Bridled Titmice, even after accounting for the difference in body size. Reduced EWL is characteristic of species from hotter, drier habitats and suggests that physiology plays a role in these species' habitat preferences. Article Birds of the open, humid lowland tropics encounter challenging thermal conditions-high temperatures, high humidity, and intense solar radiation. I examined how one such species, the Variable Seedeater (Sporophila aurita, Emberizidae), responds to temperature by measuring its body temperature (T b), metabolic heat production ($\dot{H}_{{\rm m}}$, calculated from oxygen consumption), and evaporative heat loss ($\dot{H}_{{\rm e}}$, calculated from evaporative water loss) at stable air temperatures$(T_{{\rm a}})$between 14 and 46°C. I also measured basal metabolic rate (BMR) and T b of the Variable Seedeater's diminutive (7.5 g) congener, the Ruddy-breasted Seedeater (S. minuta). All measurements utilized fasted, active-phase birds that were resting in the dark. BMR was lower than expected allometrically in both species, averaging 76% of predicted (or 0.718 kJ/h) in the 9.8-g Variable Seedeater (n = 11) and 67% of predicted (or 0.525 kJ/h) in the Ruddy-breasted Seedeater (n = 3). The Variable Seedeater's thermoneutral zone (TNZ) was relatively high (28.9 to 39.2°C). Below the TNZ,$\dot{H}_{{\rm m}}$was linearly related to T a as follows:$\dot{H}_{{\rm m}}$(kJ/h) = 2.22 - 0.052 T a. Thermal conductance, as indicated by the slope of this relation, was 12% lower than predicted allometrically. Data for 14 tropical bird species show BMR and thermal conductance to be linked; species with relatively high thermal conductance have a high BMR and vice versa. Evaporative cooling is relatively ineffective in the humid tropics, and compared with most birds Variable Seedeaters have a blunted evaporative response to heat. They dissipate evaporatively a maximum of 127% of their metabolic heat production at high T a, even when measured in air only half as humid as that of their native habitat. Consequently, Variable Seedeaters employ hyperthermia (elevated T b) to cope with heat. They are more tolerant of hyperthermia than most bird species and survive T b s that are among the highest recorded for birds (46.8 to 47.0°C). Tolerance of hyperthermia is advantageous because it allows Variable Seedeaters to maintain an unusually large$T_{{\rm b}}-T_{{\rm a}}$gradient in hot environments (0.8 to 1.4°C at T a = 43°C), and thereby to dissipate heat passively. Variable Seedeaters are able to circumvent partially the well-known temperature dependency of chemical reactions (i.e. the Arrhenius-van't Hoff effect). This enables them to become progressively hyperthermic at$T_{{\rm a}}{\rm s}$above 35°C with relatively little increase in metabolic heat production, their$\dot{H}_{{\rm m}}\$ increasing at only 52% of the allometrically predicted rate above the TNZ. Variable Seedeaters possess several traits that enhance their tolerance of high T a, yet because of their small size and limited thermal inertia their principal response to heat stress in the field is to avoid it behaviorally rather than to overcome it physiologically.