Changes in bird species distribution in four altitudinal zones in Monteverde, Costa Rica Grant Connette Department of Biology, Davidson College ABSTRACT The impact of climate change on ecosystems has been demonstrated by studies of upper elevation amphi bians Pounds 1997. In spite of this, the degree to which climate change affects birds is not as clear. Two previous studies have found the upward movement of many species of birds in the Monteverde area Donnelly 1998, Palm 2003. I surveyed birds in four altitudinal zones on the less studied Atlantic slope of the Monteverde Cloud Forest Preserve and compared my findings to the bird distributions reported by Michael Fogden in 1993. I found significant upward movement of bird species sign test, p < 0. 05 as well as a general decline in the abundances of certain bird species x 2 = 27.65, df = 3, p < 0.001. The majority of these declines are probably linked to the reforestation of the PeÃ±as Blancas valley but climate change is likely responsible for th e upslope movement and increased abundance of higher elevation birds. RESUMEN El impacto del cambio climÃ¡tico en los ecosistemas ha sido demostrado por varios estudios en anfibios que habitan las zonas altas Pounds, 1997. A pesar de esto, el hecho que el cambio climÃ¡tico afecte de alguna manera a las aves, no estÃ¡ claro. Dos estudios anteriores han encontrado que muchas especies de aves de zonas bajas estÃ¡n incrementa sus poblaciones en Monteverde Donnelly, 1998 y Palm, 2003. ExaminÃ© 4 zonas altitu dinalmente diferentes en el lado AtlÃ¡ntico de la Reserva del Bosque Nuboso Monteverde y comparÃ© mis resultados a las distribuciones de especies de aves reportadas por Michael Fogden en 1993. EncontrÃ© que algunas especies aumentaron su distribuciÃ³n en Ã¡reas de mayor altura Prueba de Muestra, p<0.05 asÃ como una declinaciÃ³n general en los abundancia de ciertas especies de aves x 2 =27.65, df=3, p<0.001. La mayorÃa de Ã©stos declines estÃ¡n relacionados probablemente a la reforestaciÃ³n del valle de PeÃ±as Bla ncas pero el cambio climÃ¡tico es probablemente responsable del movimiento ascendente y de la abundancia creciente de aves propias de zonas bajas en zonas mÃ¡s altas. INTRODUCTION Global climate change is now a well documented phenomenon but its effects on plant and animal diversity are still being studied. While birds may be able to cope with some change in temperature or moisture, it is possible that their distributions are highly dependent on changing food availability. Fruiting and flowering periods m ay respond to climate change due to the link between their phenology and abiotic triggers like rainfall. Birds relying on these plants for food could be affected by the change in fruit or nectar availability. Insects are also highly responsive to rainfal l patterns, cloudiness, temperature fluctuation, humidity and other environmental factors Janzen 1983. Insect density peaks at the lower edge of middle elevation cloud forests, where the dry season is less severe and overall productivity is higher as pl ants have lower maintenance costs on cool nights Janzen 1973. As global temperatures rise, it is possible that the lower edge of the these cloud forests will move progressively higher, driving insects and insectivorous birds upslope in pursuit of abunda nt food.
2 While food abundance could affect altitudinal distribution of bird species, the additional effect of competitive interactions must be considered. Robinson and Terborgh 1995 found that interspecific territoriality is widespread among Amazonian b irds of similar niches with adjacent territories. In every case, the less dominant species was forced to accept a less productive habitat. Tropical birds forced into less productive highlands have developed adaptations to cold or rainy weather which allo w them to be competitively superior at higher elevations. A good example of such a bird is the White Breasted Blue Mockingbird, which forages on the ground and does better when rain drives insects out of the soil Skutch 1950. This bird also significant ly increases the time it spends incubating eggs or nestlings during cold or wet conditions Skutch 1950. Warmer, drier, conditions coupled with increased food availability could put an end to facultative niche partitioning between elevations by allowing lower elevation birds to move into the previously inhospitable highlands and displace resident species. Highland birds also may have simply evolved with less competition because few species are cold weather adapted. If the highlands were to warm and make cold weather adaptations unnecessary, many new and better competitors could move into the area and displace resident species. I also expect that the arrival of nest predators, such as the Keel Billed Toucan, could cause further damage to highland bird po pulations already facing constricted habitats. A survey done in 1993 defined seven habitat zones for Monteverde area birds and the abundances of species were determined for each zone Fogden 1993. Both Donnelly 1998 and Palm 2003 have repeated the Fo gden study on the Pacific slope and found upslope movement of bird species, though to a lesser extent in the wet season. Pounds 1997 found that open country birds, which prefer fields, gaps, edges or young second growth, are losing local species diversi ty in areas of regenerating forest but that birds as a whole are losing little species diversity as a result of temperature changes. The goal of my study was to define current bird distributions on the more aseasonal Atlantic slope of the Monteverde area. I predicted that my study would show both the decline of open country birds from the Fogden study and a general upslope movement of bird species due to climate change. MATERIALS AND METHODS I spent twelve days identifying every bird encountered between the Monteverde Cloud Forest Preserve entrance and the Refugio Aleman Appendix A. I used A Guide to the Birds of Costa Rica Stiles and Skutch 1989 to identify every bird encountered. Some more secretive birds were identified by sound. I also recorde d the altitude at which each bird was spotted. I began around 5:45 AM every day and made observations on the El Camino and PeÃ±as Blancas trails. Each time I walked down, I spent the night at the shelter and walked back on the same trail. My study covered much of zones 3 6 from Fogden s study, which have approximate altitudinal ranges. Zone 4 was the highest above 1600 m on the Pacific and above 1400 m on the Atlantic Slope while zone 3 roughly 1500 1600 m was below on the Pacific slope. Zones 5 100 0 1400 m and 6 800 1000 m were lower on the Atlantic Slope. Zones 3 and 4 are cloud forests that receive around 3 m of rainfall annually while zones 5 and 6 are rainforest that receive between 4 and 8 m of rainfall annually. The cloud forest also rece ives much precipitation in the form of mist during the dry season
3 and therefore has higher epiphyte abundance than the lower Atlantic rainforest Haber et al., 2000. The Atlantic slope rainforest, zones 5 and 6, is particularly rich in ferns, aroids and large leaved herbs Haber et al 2000. I created a list of the number of individuals of each bird species I found in each zone. I then classified them into categories of abundance based on the number of individuals of each species found in a particular zo ne Table 2. Categories were roughly based on Fogden s descriptions. I called any bird found at least twice daily a common species. A fairly common species was one seen or heard daily or almost daily, usually in small numbers. An uncommon species was anything seen once or twice a week or less. I used Fogden s exact definitions for fairly common and uncommon but did not use Fogden s rare designation as the distinction between a rare and an uncommon species is impossible to make over a two week p eriod. I also used a slightly different definition of a common species to draw a clearer line than Fogden between a fairly common and a common species. Zone 3 Zone 4 Zone 5 Zone 6 Common C 4+ 6+ 8+ 4+ Fairly Common F 3 3 5 4 7 3 Uncommon U 1 2 1 2 1 3 1 2 I did not include certain birds in analysis for various reasons. Parrots and some pigeons were flocking birds that could be extremely common certain days but absent the rest of the time. Raptors and Vultures were not included because they were relatively uncommon in the closed forest. I also made no effort to sample nocturnal birds. For these groups of birds I felt that I was not able to reliably define their distributions and excluded them from analysis. Fogden also may have used different criteria for classifying Hummingbirds and I also excluded them from analysis. Many are listed as common and yet are generally solitary and are never seen frequently enough in the forest to fit Fogden s definition of a common species one seen s everal times daily in moderate to large numbers . To determine whether or not abundances have changed since 1993, I compared my observed species abundances for the remaining birds in each zone with those reported by Fogden Chi squared test. I isolate d those species that appeared to have moved up or down slope and determined whether these changes were significant sign test. RESULTS I identified 114 different species of birds in zones 3 6. Of these, 29 showed noticeable differences in their elevat ional range since Fogden s 1993 study Table 2. Nine of these species moved down in elevation while 20 moved up. Fourteen of the 20 that moved up had expanded into zones where Fogden had not found them. A sign test Table 1. Abundance designations. The number of individuals of a species that must be seen for that species to be c onsidered Common, Fairly Common or Uncommon in a particular zone. The number of individuals required for a species to fit into a category varied between zones due to uneven sampling time.
4 suggested that birds have made a sign ificant movement upslope since 1993 sign test, n = 29, p < 0.05. Many birds have also changed in overall abundance since Fogden s study, though these changes were not distributed equally across zones. Zones 3 and 6 showed far more species declines than species increases 13 vs. 4 in zone 3, 20 vs. 0 in zone 6. Zone 5 also showed more declining species than increasing species 34 vs. 12. Zone 4, however, had more species increasing in abundance than decreasing in the time since Fogden s study 15 vs. 13. Groups that seem to show the greatest decline in abundance were the flycatchers, antbirds, sparrows, finches and some tanagers. Woodcreepers, warblers and wrens showed no noticeable change in abundance. The majority of species increasing in abunda nce within any given zone were the result of up or downslope expansion into territory where they previously were not found. Changes in bird abundance showed a significant difference between my data and Fogden s data Chi squared goodness of fit test, x 2 = 27.65; df = 3; p < 0.001. DISCUSSION It is not surprising that birds have changed in abundance over the 13 years since Fogden s study. In 1993, the Bosque Eterno de los NiÃ±os had been in existence for less than ten years. At this time, clearings wer e probably just returning to shorter, second growth forest cover. Many bird species that thrive in open country or forest clearings were very dominant and have showed a large scale decline over the past 13 years. Nearly all of the flycatchers are more pre valent in open areas, forest clearings, or young secondary growth Stiles and Skutch 1989 and showed a large decline in abundance. The Tufted Flycatcher was the only exception to the trend in the data, yet I typically found it in small clearings, treefal l gaps and along streams. The Tanagers that showed decline are reported to frequent the canopy and edge of dense forest Stiles and Skutch 1989. They were said to come closer to the ground in second growth or in nearby clearings with scattered trees. T anagers, which are primarily frugivorous, now feed in a much higher canopy or more isolated clearings and are less common and harder to spot than they were 13 years ago. This expectation was supported by my study, as a large percentage of Tanagers spotted were in the clearing around the Refugio Aleman. Daily altitudinal movements were not a factor as the Tanagers were in the clearing around the Refugio both in the early and late morning. Common Bush Tanagers were still extremely abundant, yet they are ge neralists known for leading mixed foraging flocks through all types of forest. Sparrows, Seedeater, Finches and Grosbeaks also typically frequent clearings, fields and shrubby second growth in search of seeds Stiles and Skutch 1989 and have decreased in abundance along with these sorts of habitats in the PeÃ±as Blancas valley. The decline of the Antbirds is more puzzling, as they are usually found in dense forests. It is possible that Antbirds are very sensitive to changes in habitat and have still not recovered from declines following historical deforestation. It is also possible that two weeks was not sufficient time to come across enough groups of Army Ants followed by Antbirds. From experience, Antbirds were encountered following large Army Ant rai ds and large Army Ant columns were simply not seen often enough to make Antbird sightings frequent. With the exception of the Antbirds, all groups of birds showing decline seemed to have a likely habitat change as an explanation.
5 Some of these perceived decreases in abundance may be due to the greater ability of Fogden, a long time researcher, to spot birds. It is probably the case that, while many species appear to have changed in abundance, only the groups showing the largest differences in abundance c ompared to other groups have experienced an actual change. The increase in abundance of higher elevation birds is also an important change, as this showed up in spite of overall decline in sightings compared to Fogden. When comparing the number of bird species that obviously moved up or down in distribution since 1993, there is more certainty. Birds found in a higher zone than they were ever found in before have definitely shifted their actual ranges upslope. The twenty birds moving upslope had either moved into an entirely new habitat zone or were more common than before at high altitudes and much less common at lower altitudes. Furthermore, three of the nine bird species moving downslope were Tanagers that were only found in the clearing around the R efugio Aleman. These shifts were probably due to changing habitat and do not accurately reflect a new altitude preference. Overall, however, there was a general trend of upslope movement. While many birds may move upslope for breeding or for food, birds found in entirely new habitat zones are more than likely moving outside of their traditional ranges, even for breeding or migration. Perhaps the best examples of such movement are the Redstarts. The Collared Redstart is now found only in the higher part s of Zone 4 and the Slate throated Redstart, which was not found in zone 4 by Fogden, is now common in zone 4. This movement was also noted by both Palm 2003 and Donnelly 1998. While there are many examples of birds moving upslope, the impact of thes e movements is not yet known. One possible indicator species is the Sooty capped Bush Tanager, which is found only in zone 4. This species was fairly common in Fogden s study yet was never observed in my study, even at altitudes as high as 1700 m. The C ommon Bush Tanager, on the other hand, was extremely abundant at all levels of zone 4. Discerning the effects of climate change on bird distributions is complicated by forest regeneration at lower elevations, yet the Monteverde Cloud Forest Preserve has b een protected for a long time and movements into zone 4 cannot be ascribed to habitat changes there. The reliability of Fogden s data also ensures that changes in bird ranges are recent and significant. Climate change is implicated where all other possibi lities fail. Amphibians were an early indicator of global climate change, but for current levels of temperature and rainfall change to affect birds there probably needs to be a much larger effect on the ecosystem as a whole. Endothermic organisms are unl ikely to be directly affected by fairly small temperature changes and are more likely to move upslope in response to changes in the biotic systems they depend on. The upward movement of birds coupled with the effects of competitive interactions suggest th at further changes in bird abundance and distribution are likely to take place in the near future. Research on changing species interactions due to upslope movement is needed to complete the picture of climate change s effects on birds. Only further stud y on a much larger scale can alert people to the fact that there is a lot more to lose than a few highland amphibians as a result of global warming.
6 ACKNOWLEDGEMENTS I would like to thank Tania Chavarria Pizzaro and Alan Masters for their constant adv ice and support with this project. I would also like to thank Karen Masters, Tom McFarland and Camryn Pennington for everything they helped with along the way. Thanks also to the Monteverde Cloud Forest Preserve for letting me use their land. Finally, t hank you to Kaitlin Dunn, Josh Metten and the three men from the power company who kept me company during my research. LITERATURE CITED Donnelly, E. 1998. Changes in Bird Species Composition in Four Habitat Zones in Monteverde, Costa Rica. CIEE Spri ng. Fogden, M. 1993. An Annotated Checklist of the Birds of Monteverde and PeÃ±as Blancas. San JosÃ©, Costa Rica. Haber, W. A., W. Zuchowski and E. Bello. 2000. An Introduction to Cloud Forest Trees; Monteverde, Costa Rica. Mountain Gem Publicati ons, Monteverde de Puntarenas, Costa Rica. Janzen, D. H. 1973. Sweep samples of tropical foliage insects: Effects of seasons, vegetation types, elevation, time of day, and insularity. Ecology , 54:687 708. Janzen, D.H. 1983. Insects Introduction. In Costa Rican Natural History , D.H. Janzen ed., The University of Chicago Press, Chicago, IL. Palm, E. 2003. Patterns of Seasonal and Altitudinal Change in Monteverde Bird Communities. CIEE Fall. Pounds, A. J., M. P.L. Fogden, J. M. Savage and G . C. Gorman. 1997. Tests of Null Models for Amphibian Declines on a Tropical Mountain. Conservation Biology, Vol. 11, No. 6. Skutch, A. F. 1950. Life History of the White Breasted Blue Mockingbird. The Condor, 52 5: 220 227. Stiles, G. F. and A . F. Skutch. 1989. A Guide to the Birds of Costa Rica. Cornell, NY. Robinson, S. K. and J. Terborgh. 1995. Interspecific Aggression and Habitat Selection by Amazonian Birds. The Journal of Animal Ecology, 64 1: 1 11.
7 TABLES SPECIES Fogden Connette Fogden Connette Fogden Connette Fogden Connette Â² Black Guan F U 2 F C 16 F C 17 + Great Curassow U 2 + Black-breasted Wood Quail F C 12 F F U 3 F Chiriqui Quail-Dove R U 1 R + Buff-fronted Quail-Dove U F U U 3 R Hoffman's Woodpecker * U 1 + Plain Xenops U 2 U + Ruddy Treerunner * U 2 F C 9 Wedge-billed Woodcreeper * U 1 U 1 F F 5 F + Spotted Woodcreeper C C 6 C C C 12 C Buff-throated Foliage-gleaner U 3 F + Striped Foliage-gleaner U 1 F + Dull-mantled Antbird U 1 R + Striped-breasted Wren U 1 C + Tennessee Warbler U U 2 C C 13 C + Buff-rumped Warbler * F U 1 F C 7 Tropical Parula U U 2 C F 5 C + Black-and-white Warbler F U 1 U 1 F C 15 F U 1 + Wilson's Warbler C U C 6 C C 13 C C 5 + Slate-throated Redstart C C 11 C 17 C C 52 U U 1 + Olive-crowned Yellowthroat U 2 C U 1 C U 2 + Northern Oriole U U 2 U F 4 F + Tawny-capped Euphonia U 2 F U 2 F + Scarlet-thighed Dacnis C U C C C 5 Black-and-Yellow Tanager U 1 F U 1 + Crimson-collared Tanager * C C C 8 Scarlet-rumped Tanager C U 1 C C 17 Yellow-thighed Finch F C 6 U 2 Variable Seedeater U 1 U C U 2 + Zone 3 Zone 4 Zone 5 Zone 6 Table 2. Twenty nine bird species wi th ranges that moved up or down in elevation. + refers to upslope movement refers to downslope movement C=Common, F=Fairly Common, U=Uncommon, R=Rare, *=Vagrant outside normal range Numbers in parenthesis are the actual numbers of individuals fou nd in this study for each zone.
8 APPENDIX Appendix A: Map of Zones 3 6 in the Monteverde Cloud Forest Preserve and surrounding area Fogden 1993 Appendix B: Full data sheet Number of individuals of each species found in each zone. SPECIES Zone 3 Zone 4 Zone 5 Zone 6 Black Guan 1 8 17 Great Curassow 2 Black breasted Wood Quail 4 8 3 Turkey Vulture 5 5 Black Vulture 1 Bicolored Hawk 1 Broad winged Hawk 4 Black Chested Hawk 2 Band tailed Pigeon 71 Short billed Pigeon 1
9 Chiri qui Quail Dove 1 Buff fronted Quail Dove 3 Brown hooded Parrot 5 White collared Swift 14 Vaux's Swift 18 Green Hermit 1 4 1 Green Violet ear Violet Sabrewing 3 Purple crowned Fairy Green cowned Brilliant 2 White bellied Mountain gem Purple throated Mountain gem 3 Steely vented Hummingbird 1 Striped tailed Hummingbird 1 Coppery headed Emerald 1 Magenta throated Woodstar 2 Orange bellied Trogon 2 7 Rufous Tailed Jacamar 4 Emerald Toucanet 3 Prong billed Barbet 4 9 7 Red headed Barbet 5 Golden olive Woodpecker 1 1 Smoky brown Woodpecker 1 1 Hoffman's Woodpecker 1 Plain Xenops 2 Ruddy Treerunner 1 10 Spotted Barbtail 9 10 Wedge billed Woodcreeper 2 5 Olivacious Woodcreeper 2 1 Brown billed Scythebill 1 Spotted Woodcreeper 3 3 12 Buff throated Foliage gleaner 3 Striped Foliage gleaner 1 Lineated Foliage gle aner 1 1 Streaked breasted Treehunter 1 Gray throated Leaftosser Tawny throated Leaftosser 1 1 Red faced Spinetail 2 Russet Antshrike 1 Dusky Antbird Immaculate Antbird 3 Dull mantled Antbird 1 Slaty Antwren 2 Plain Antvireo 1
10 Golden bellied Flycatcher 1 Torrent Tyrannulet 2 Olive sided Flycatcher 1 Black Phoebe 1 Eastern Wood Pewee 1 Tufted Flycatcher 2 54 11 Yellowish Flycatcher Yell ow bellied Flycatcher Olive striped Flycatcher 1 2 White throated Spadebill 1 3 Scale crested Pygmy Tyrant 2 Common Tody Flycatcher 2 Mistletoe Tyrannulet 1 5 Mountain Elaenia 1 1 Striped breasted Wren 1 Gr ay breasted Wood Wren 9 83 92 4 Ochraceous Wren 6 9 2 Nightengale Wren 2 Slaty backed Nightengale Thrush 3 1 Swainson's Thrush 1 1 Wood Thrush 1 Mountain Robin 1 Clay colored Robin 1 8 Black faced Solitaire 3 70 19 Azure hooded Jay 12 29 1 Lesser Greenlet 1 2 1 Golden crowned Warbler 2 1 Three striped Warbler 5 64 26 Tennessee Warbler 2 13 Buff rumped Warbler 1 7 Bananaquit 1 2 1 Tropical Parula 2 5 Golden winged Warbler 3 4 Blu e winged Warbler 2 Black and white Warbler 2 15 1 Wilson's Warbler 6 13 5 Collared Redstart 32 Slate Throated Redstart 4 24 52 1 Olive crowned Yellowthroat 2 1 2 Cerulean Warbler 2 Chestnut sided Warbler 4 3 Black throat ed Green Warbler 8 1 Louisiana Waterthrush 1 Northern Oriole 2 4
11 Tawny capped Euphonia 2 2 Golden browed Chlorophonia 3 1 Blue and Gold Tanager 3 Common Bush Tanager 121 137 2 Scarlet thighed Dacnis 5 Silver thro ated Tanager 12 14 4 Green Honeycreeper 2 Bay headed Tanager 2 6 Spangled cheeked Tanager 3 Black and yellow Tanager 1 1 Blue gray Tanager 2 Crimson collared Tanager 8 Scarlet rumped Tanager 1 17 Hepatic Tanage r 2 Black throated Saltator 1 Black thighed Grosbeak 2 Chestnut capped Brush Finch 1 4 Sooty faced Finch 5 Yellow thighed Finch 6 2 Variable Seedeater 1 2 Blue Seedeater 1 Rufous collared Sparrow 4 B lack striped Sparrow 1 Zone 3 total Zone 4 total Zone 5 total Zone 6 total Total=1490 35 558 783 114
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Cambios en la distribucin de especies de aves en cuatro zonas de altitud en Monteverde, Costa Rica
Changes in bird species distribution in four altitudinal zones in Monteverde, Costa Rica
The impact of climate change on ecosystems has been demonstrated by studies of upper elevation amphibians (Pounds 1997). In spite of this, the degree to which climate change affects birds is not as clear. Two previous studies have found the upward movement of many species of birds in the Monteverde area (Donnelly 1998, Palm 2003). I surveyed birds in four altitudinal zones on the less studied Atlantic slope of the Monteverde Cloud Forest Preserve and compared my findings to the bird distributions reported by Michael Fogden in 1993. I found significant upward movement of bird species (sign test, p < 0.05) as well as a general decline in the abundances of certain bird species (x2 = 27.65, df = 3, p < 0.001). The majority of these declines are probably linked to the reforestation of the Peas Blancas valley but climate change is likely responsible for the upslope movement and increased abundance of higher elevation birds.
El impacto del cambio climtico en los ecosistemas ha sido demostrado por varios estudios en anfibios que habitan en las zonas altas (Pounds, 1997). A pesar de esto, el hecho que el cambio climtico afecte de alguna manera a las aves, no esta claro. Dos estudios anteriores han encontrado que muchas especies de aves de las zonas bajas estn incrementando sus poblaciones en Monteverde (Donnelly, 1998 y Palm, 2003). Examine 4 zonas altitudinalmente diferentes en el lado Atlntico de la Reserva del Bosque Nuboso de Monteverde y compare mis resultados con las distribuciones de especies de aves reportadas por Michael Fogden en 1993.
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Tropical Ecology 2006
Ecologa Tropical 2006
t Monteverde Institute : Tropical Ecology