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Avian population trends in Scalesia forest on Floreana Island (2004-2013): Acoustical surveys cannot detect hybrids of Darwin’s tree finches Camarhynchus spp.



Floreana Island has the highest proportion of local land bird extinctions on the Galápagos Archipelago, and is home to the range-restricted and critically endangered Medium Tree Finch Camarhynchus pauper. We used acoustic surveys during 2004, 2008 and 2013 to compare the estimated population size of C. pauper and other land bird species in a remnant patch of Scalesia forest. First, we compared song in C. pauper and C. parvulus and the recently discovered Camarhynchus hybrid group to justify our use of acoustic surveys to detect population trends given contemporary hybridisation between C. pauper and C. parvulus. Song differed significantly between C. pauper versus C. parvulus and hybrid birds, but not between C. parvulus versus hybrid birds. Second, we compared population size estimates. Camarhynchus pauper declined by 52% between 2004 and 2013 (with a 10% increase since 2008); C. parvulus/hybrid increased by 45% between 2004 and 2013 (with 28% decrease since 2008). In 2013, there were ∼ 419 C. pauper males in the Scalesia forest (estimate for Scalesia habitat only) and ∼ 2,537 males on Floreana Island (estimate for the entire available highland habitat). Not all species showed a pattern of decline in the highland Scalesia habitat between 2004 and 2013: Dendroica petechia (+256%), Crotophaga ani (+254%) Geospiza fuliginosa (+23%), and Myiarchus magnirostris (+11%) increased, while the ground finch G. fortis (-76%) decreased. Understanding why C. pauper is declining while other land bird species are increasing in the same habitat requires continued inquiry and monitoring efforts.


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Allendorf, F. W., Leary, R. F., Spruell, P. and Wenburg, J. K. (2001) The problems with hybrids: Setting conservation guidelines. Trends Ecol. Evol. 16: 613622.
Andersone, Ž., Lucchini, V. and Ozoliņš, J. (2002) Hybridisation between wolves and dogs in Latvia as documented using mitochondrial and microsatellite DNA markers. Mammal. Biol. - Z. Säugetierk. 67: 7990.
Baillie, J. E. M., Hilton-Taylor, C. and Stuart, S. N. (2004) 2004 IUCN Red List of Threatened species. A global species assessment. Cambridge. UK: IUCN Press.
Baskett, M. L. and Gomulkiewicz, R. (2011) Introgressive hybridization as a mechanism for species rescue. Theor. Ecol. 4: 223239.
Bowman, R. I. (1983) The evolution of song in Darwin’s finches. In Bowman, R. I., Berson, M. and Leviton, A. E., eds. Patterns of evolution in Galápagos Organisms. San Francisco, California, USA: Pacific Division AAAS.
Bowman, R. I., Berson, M., Leviton, A. E. and American Association for the Advancement of Science. Pacific Division. (1983) Patterns of evolution in Galapagos organisms. San Francisco, California: Pacific Division, AAAS.
Buckland, S. T., Anderson, D. R., Burnham, K. P., Laake, J. L., Borchers, D. and Thomas, L. (2001) Introduction to distance sampling. New York, USA: Oxford University Press.
Catchpole, C. K. and Slater, P. J. (2003) Bird song: biological themes and variations. Cambridge, UK: Cambridge University Press.
Christensen, R., Kleindorfer, S. and Robertson, J. (2006) Song is a reliable signal of bill morphology in Darwin’s small tree finch Camarhynchus parvulus, and vocal performance predicts male pairing success. J. Avian Biol. 37: 617624.
Connett, L., Guézou, A., Herrera, H. W., Carrión, V., Parker, P. G. and Deem, S. L. (2013) Gizzard contents of the smooth-billed ani Crotophaga ani in Santa Cruz, Galápagos Islands, Ecuador. Galápagos Research, 68. Published online, 15 November 2013.
Cunninghame, F., Ortiz-Catedral, L. and Fessl, B. (2012) Landbird conservation plan: Strategies for reversing the decline of passerine birds on the Galapagos Islands. In Secondary report of the workshop: Searching for solutions for the control of the avian parasite, Philornis downsi, Puerto Ayora, Santa Cruz, Galápagos. Vol. 31. Puerto Ayora, Santa Cruz, Galapagos: Charles Darwin Foundation and Galapagos National Park Service.
Dawson, D. K. and Efford, M. G. (2009) Bird population density estimated from acoustic signals. J. Appl. Ecol. 46: 12011209.
Derégnaucourt, S., Guyomarc’h, J. C. and Richard, V. (2001) Classification of hybrid crows in quail using artificial neural networks. Behav. Process. 56: 103112.
Driscoll, D. A. (1998) Counts of calling males as estimates of population size in the endangered frogs Geocrinia alba and G. vitellina. J. Herpetol. 32: 475481.
Dvorak, M., Fessl, B., Nemeth, E., Kleindorfer, S. and Tebbich, S. (2012) Distribution and abundance of Darwin’s finches and other land birds on Santa Cruz Island, Galápagos: evidence for declining populations. Oryx 46: 78.
Dvorak, M., Vargas, H., Fessl, B. and Tebbich, S. (2004) On the verge of extinction: a survey of the mangrove finch Cactospiza heliobates and its habitat on the Galápagos Islands. Oryx 38: 171179.
Fowler, A. C., Eadie, J. M. and Engilis, A Jr. (2009) Identification of endangered Hawaiian ducks (Anas wyvilliana), introduced North American mallards (A. platyrhynchos) and their hybrids using multilocus genotypes. Conserv. Genet, 10: 17471758.
Goodale, E. and Podos, J. (2010) Persistence of song types in Darwin’s finches, Geospiza fortis, over four decades. Biol. Lett. 6: 589592.
Grant, B. R. and Grant, P. R. (1993) Evolution of Darwin’s finches caused by a rare climatic event. Proc. R. Soc. Lond. B Biol. Sci. 251: 111117.
Grant, B. R. and Grant, P. R. (1996) Cultural inheritance of song and its role in the evolution of Darwin’s finches. Evolution 50: 24712487.
Grant, P. R. (1986) Ecology and evolution of Darwin’s finches, Princeton, USA: Princeton University Press.
Grant, P. R. and Grant, B. R. (1992) Hybridization of bird species. Science 256: 193197.
Grant, P. R. and Grant, B. R. (1997) Hybridization, sexual imprinting, and mate choice. Am. Nat. 149: 128.
Grant, P. R. and Grant, B. R. (2014a) Synergism of natural selection and introgression in the origin of a new species. Am. Nat. 183: 671681.
Grant, P. R. and Grant, B. R. (2014b) Synergism of natural selection and introgression in the origin of a new species. Am. Nat. 183: 671681.
Grant, P., Curry, R. and Grant, B. (2000) A remnant population of the Floreana mockingbird on Champion Island, Galápagos. Biol. Conserv. 92: 285290.
Grant, P. R., Grant, B. R., Keller, L. F., Markert, J. A. and Petren, K. (2003) Inbreeding and interbreeding in Darwin’s finches. Evolution 57: 29112916.
Grant, P. R., Grant, B. R. and Petren, K. (2005a) Hybridization in the recent past. Am. Nat. 166: 5667.
Grant, P. R., Grant, B. R., Petren, K. and Keller, L. F. (2005b) Extinction behind our backs: the possible fate of one of the Darwin’s finch species on Isla Floreana, Galápagos. Biol. Conserv. 122: 499503.
Hails, C. (2008) Living planet report 2008. Zürich, Switzerland: WWF International.
Hamilton, J. A. and Miller, J. M. (2016) Adaptive introgression: A resource for management and genetic conservation in a changing climate. Conserv. Biol. 30: 3341.
Hebert, P. D. N., Penton, E. H., Burns, J. M., Janzen, D. H. and Hallwachs, W. (2004) Ten species in one: DNA barcoding reveals cryptic species in the neotropical skipper butterfly Astraptes fulgerator. Proc. Natl. Acad. Sci. 101: 1481214817.
IUCN (2015) The IUCN Red List of Threatened Species. Version 2015.1.
Jiménez-Uzcátegui, G., Carrión, V., Zabala, J., Buitrón, P. and Milstead, B. (2008) Status of introduced vertebrates in Galápagos. Pp. 136141 in Galápagos Report 2006–2007. Puerto Ayora, Galapagos, Ecuador: GNPS, GCREG, CDF and GC.
Karanth, K. U. and Nichols, J. D. (2010) Non-invasive survey methods for assessing tiger populations. Pp. 241261 in Tilson, R. and Nyhus, P. J., eds. Tigers of the world: The science, politics and conservation of Panthera tigris. London, UK and Burlington, MA: Academic Press.
Kleindorfer, S. and Dudaniec, R. Y. (2016) Host-parasite ecology, behavior and genetics: a review of the introduced fly parasite Philornis downsi and its Darwin’s finch hosts. BMC Zoology 1: 119.
Kleindorfer, S. and Sulloway, F. J. (2016) Naris deformation in Darwin’s finches: experimental and historical evidence for a post-1960s arrival of the parasite Philornis downsi. Global Ecol. Conserv. 7: 122131.
Kleindorfer, S., Custance, G., Peters, K. J. and Sulloway, F. J. (In review) Parasites change pre-mating signal and blur species boundaries: Philornis downsi and Darwin’s finches (Camarhynchus spp.). PNAS.
Kleindorfer, S., O’Connor, J. A., Dudaniec, R. Y., Myers, S. A., Robertson, J. and Sulloway, F. J. (2014a) Species collapse via hybridization in Darwin’s tree finches. Am. Nat. 183: 325341.
Kleindorfer, S., Peters, K. J., Custance, G., Dudaniec, R. Y. and O’Connor, J. A. (2014b) Changes in Philornis infestation behavior threaten Darwin’s finch survival. Curr. Zool. 60: 542550.
Kleindorfer, S., Peters, K. J., Hohl, L. and Sulloway, F. J. (2016) Flight behaviour of an introduced parasite affects its Galápagos Island hosts: Philornis downsi and Darwin’s finches. Pp. 158179 in Weis, J. S. and Sol, D., eds. Biological invasions and behaviour. Cambridge, UK: Cambridge University Press.
Lack, D. L. (1983) Darwin’s finches. Cambridge, UK: Cambridge University Press.
Lambert, K. T. A. and Mcdonald, P. G. (2014) A low-cost, yet simple and highly repeatable system for acoustically surveying cryptic species. Austral. Ecol. 39: 779785.
López-Pujol, J., Garcia-Jacas, N., Susanna, A. and Vilatersana, R. (2012) Should we conserve pure species or hybrid species? Delimiting hybridization and introgression in the Iberian endemic Centaurea podospermifolia. Biol. Conserv. 152: 271279.
Marques, T. A., Thomas, L., Ward, J., DiMarzio, N. and Tyack, P. L. (2009) Estimating cetacean population density using fixed passive acoustic sensors: an example with Blainville’s beaked whales. J. Acoust. Soc. Am. 125: 19821994.
Marten, K. and Marler, P. (1977) Sound transmission and its significance for animal vocalization. Behav. Ecol. Sociobiol. 2: 271290.
Martin, T. E., Paine, C. R., Conway, C. J., Hochachka, W. M., Allen, P. and Jenkins, W. (1997) BBIRD field protocol. Montana, USA: University of Montana Cooperative Wildlife Research Unit, US Geological Survey.
Mauchamp, A. (1997) Threats from alien plant species in the Galápagos Islands. Conserv. Biol. 11: 260263.
McKay, B. D. and Zink, R. M. (2014) Sisyphean evolution in Darwin’s finches. Biol. Rev. 90: 689698.
Merlen, G. (2013) Gone, gone… going: The fate of the Vermilion Flycatcher on Darwin’s Islands. Pp. 180188 in Galápagos Report 2011–2012. Puerto Ayora, Galápagos, Ecuador: GNPS, GCREG, CDF and GC.
O’Connor, J. A., Dudaniec, R. Y. and Kleindorfer, S. (2010a) Parasite infestation and predation in Darwin’s small ground finch: contrasting two elevational habitats between islands. J. Trop. Ecol. 26: 285292.
O’Connor, J. A., Robertson, J. and Kleindorfer, S. (2010b) Video analysis of host-parasite interactions in nests of Darwin’s finches. Oryx 44: 588594.
O’Connor, J. A., Sulloway, F. J. and Kleindorfer, S. (2010c) Avian population survey in the Floreana highlands: is Darwin’s medium tree finch declining in remnant patches of Scalesia forest? Bird Conserv. Internatn. 20: 343353.
O’Connor, J. A., Sulloway, F. J., Robertson, J. and Kleindorfer, S. (2010d) Philornis downsi parasitism is the primary cause of nestling mortality in the critically endangered Darwin’s medium tree finch (Camarhynchus pauper). Biodivers. Conserv. 19: 853866.
Olivares, A. and Munves, J. A. (1973) Predatory behaviour of the smooth-billed ani. The Auk 90: 891.
Ottenburghs, J., Ydenberg, R. C., Van Hooft, P., Van Wieren, S. E. and Prins, H. H. (2015) The Avian hybrids project: gathering the scientific literature on avian hybridization. Ibis 157: 892894.
Parker, P. G., Buckles, E. L., Farrington, H., Petren, K., Whiteman, N. K., Ricklefs, R. E., Bollmer, J. L. and Jimenez-Uzcategui, G. (2011) 110 years of Avipoxvirus in the Galápagos Islands. PLoS One 6: e15989.
Peters, K. J. (2016) Unravelling the dynamics of hybridisation and its implications for ecology and conservation of Darwin’s tree finches. PhD Thesis, Flinders University, Adelaide, South Australia.
Peters, K. J. and Kleindorfer, S. (2015) Divergent foraging behavior in a hybrid zone: Darwin’s tree finches (Camarhynchus spp.) on Floreana Island. Curr. Zool. 61: 181190.
Podos, J. (2001) Correlated evolution of morphology and vocal signal structure in Darwin’s finches. Nature 409: 185188.
Rentería, J. L., Gardener, M. R., Panetta, F. D., Atkinson, R. and Crawley, M. J. (2012) Possible Impacts of the invasive plant Rubus niveus on the native vegetation of the Scalesia forest in the Galápagos Islands. PLoS ONE 7: e48106.
Reynolds, R. T., Scott, J. M. and Nussbaum, R. A. (1980) A variable circular-plot method for estimating bird numbers. Condor 82: 309313.
Rhymer, J. M. and Simberloff, D. (1996) Extinction by hybridization and introgression. Annu. Rev. Ecol. Syst. 27: 83109.
Roberts, D. G., Gray, C. A., West, R. J. and Ayre, D. J. (2010) Marine genetic swamping: hybrids replace an obligately estuarine fish. Mol. Ecol. 19: 508520.
Schluter, D., Price, T. D. and Grant, P. R. (1985) Ecological character displacement in Darwin’s finches. Science 227: 10561059.
Scott, J. M., Ramsey, F. L. and Kepler, C. B. (1981) Distance estimation as a variable in estimating bird numbers from vocalizations. Stud. Avian Biol. 6: 334340.
Simberloff, D. (1995) Habitat fragmentation and population extinction of birds. Ibis 137: S105S111.
Sinclair, A. R., Fryxell, J. M. and Caughley, G. (2009) Wildlife conservation and management. Pp. 217383 in Sinclair, A. R. and Fryxell, J. M., eds. Wildlife ecology, conservation and management. Carlton: Blackwell Publishing.
Steadman, D. W. (1986) Holocene vertebrate fossils from Isla Floreana, Galápagos, Washington DC: Smithsonian Institution Press.
Thomas, L., Buckland, S. T., Burnham, K. P., Anderson, D. R., Laake, J. L., Borchers, D. L. and Strindberg, S. (2006) Distance sampling. Pp. 687697 in El-Shaarawi, A.-H. and Piegorsch, W., eds. Encyclopedia of environmetrics. Chichester, UK: John Wiley and Sons, Ltd.
Toews, D. P. L. and Irwin, D. E. (2008) Cryptic speciation in a Holarctic passerine revealed by genetic and bioacoustic analyses. Mol. Ecol. 17: 26912705.
Vilà, C., Walker, C., Sundqvist, A.-K., Flagstad, Ø., Andersone, Z., Casulli, A., Kojola, I., Valdmann, H., Halverson, J. and Ellegren, H. (2003) Combined use of maternal, paternal and bi-parental genetic markers for the identification of wolf–dog hybrids. Heredity 90: 1724.
Watson, J., Trueman, M., Tufet, M., Henderson, S. and Atkinson, R. (2010) Mapping terrestrial anthropogenic degradation on the inhabited islands of the Galápagos Archipelago. Oryx 44: 7982.
Whiteman, N. K., Goodman, S. J., Sinclair, B. J., Walsh, T., Cunningham, A. A., Kramer, L. D. and Parker, P. G. (2005) Establishment of the avian disease vector Culex quinquefasciatus Say, 1823 (Diptera: Culicidae) on the Galápagos Islands, Ecuador. Ibis 147: 844847.
Wiedenfeld, D. A. (2006) Aves, the Galápagos Islands, Ecuador. Check List 2: 127.
Wiedenfeld, D. A. and Jiménez-Uzcátegui, G. (2008) Critical problems for bird conservation in the Galápagos Islands. Cotinga 29: 2227.
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