HM231 – Assessing detectability of under-represented species in Cusuco National Park
Tom Martin & Fabiola Rodriguez
Birds are perhaps the best-known of all vertebrate taxa in the tropics. This in part stems from
their greater inherent detectability compared to other faunal groups, and is also because a range
of methods has been carefully developed over the last 40 years which has allowed bird
communities to be surveyed in increasingly effective and efficient ways. However, while
sampling bird communities as a whole may be comparatively straightforward compared to other,
more cryptic, taxa, not all bird species are inherently simple to detect nor do they respond
equally well to the same methods. As such, while the primary methods typically employed by
ornithologists in tropical ecosystems are usually capable of detecting a majority of species, a
significant section of the community is often missed or remains under-detected by these
techniques, and this can lead to significant gaps in the understanding of the composition,
ecology, and conservation of tropical bird assemblages.
Perhaps the two most common methods employed by ornithologists in tropical forests are pointcounts and mist-nets. Point-counts involve identifying and counting all birds seen and heard
while conducting a series of timed counts at dawn along a series of pre-determined plots, and
mist-netting involves catching birds in fine-mesh nets, identifying them, marking them with
bands, and releasing them. Together these methods complement each other very well and are
capable of detecting most bird species in tropical forest ecosystems. As such they have formed
the core of the survey work conducted in Parque Nacional Cusuco (PNC) in the past. However,
both methods are also subject to certain biases and limitations that leave important sections of
avifauna communities under-recorded. A number of other secondary methods may therefore be
necessary to obtain a complete understanding of bird assemblages in tropical forests. However,
the effectiveness of most secondary methods remains poorly explored, both in tropical forests
generally and Mesoamerican cloud forest specifically.
Students working on this project will explore which secondary methods can be best utilized to
detect and survey the more cryptic bird groups of PNC which are poorly represented by pointcounts and mist-nets. This can be approached by either a community-scale investigation or a
narrower, more group-specific study.
Students examining this topic on a broad community-scale could first use secondary sources to
determine which of the approximately 250 species found in PNC have been regularly recorded
by point-counts and mist-nets in previous years, and which are largely missed by these methods.
A checklist of target species could then be produced for the students to focus on with the
secondary methods techniques. Under-recorded species on the checklist could also be sorted into
categorical groupings (ie – nocturnal birds, aerial feeders, diurnal raptors, understory insectivores
etc). Students can then experiment with a wide range of secondary methods to determine which
techniques, or combinations of techniques, are capable of detecting the greatest number species
in these under-recorded groups in the most efficient time scales. Secondary methods that could
be experimented with in this study include vocalization play-back of specific species, nocturnal
surveys, spot-mapping, noon raptor counts, and extended vigils from prominent vantage points.
The effectiveness of each secondary method can be evaluated in the context of how many target
species are detected per person-hour of survey work. Ultimately, students would be able to make
recommendations as to which combination of methods would be most efficient in describing the
full avian diversity of Mesoamerican cloud forests. Ambitious projects could also incorporate
mist-net and point-count data, and examine which choice of methods, and how many surveyhours of each method, could most effectively be used by a group of hypothetical ornithologists
setting out to describe the avifauna of a previously unstudied cloud forest ecosystem.
There are also several possibilities in this research theme for students to focus on how best to
survey a specific group of under-recorded birds. A project could, for example, concentrate on
how best to use play-back calls to record richness and abundance of Ovenbirds (Furnariidae) – a
group of cryptic understory birds found in PNC. Students could also focus on how to survey the
Park’s nocturnal birds in the most efficient way, evaluating the effectiveness of nocturnal pointcounts, line-transects and species-specific play-back, and noting which time periods are most
effective for obtaining responses from each nocturnal species.
In summary, a wide range of possibilities exist in PNC for students to undertake highly original
avian methodological studies. However, as some aspects of these projects may require some
fairly specialized equipment, or require some advanced preparation such as the downloading of
certain species calls before the start of the expedition, it is strongly recommended that students
interested in this study theme contact their field supervisors at an early stage to ensure that the
necessary equipment and preparations can be organized in advance.
Suggested Reading
Gardner, T.A., Barlow, J., Araujo, I.S., Avila-Pires, T.C., Bonaldo, A.B., Costa, J.E., Esposito,
M.C., Ferreira, L.V., Hawes, J., Hernandez, M.I.M., Hoogmoed, M.S., Leite, R.N., Lo-ManHung, N.F., Malcom, J.R., Martins, M.B., Mestre, L.A.M., Miranda-Santos, R., Overal, W.L.,
Parry, L., Peters, S.L., Riberiro-Junior, M.A., da Silva, M.N.F., Motta, C., Peres, C.A. (2008)
The cost-effectiveness of biodiversity surveys in tropical forests. Ecology Letters 2: 139-150.
Bibby, C.J., Burgess, N.D., Hill, D.A. & Mustoe, S.H. (2002) Bird Census Techniques (Second
edition). Academic press: London.
Blake, J. G., & Loiselle, B.A. (2001). Bird assemblages in second-growth and old-growth
forests, Costa Rica; perspectives from mist nets and point counts. Auk 118: 304―326.
Blake, J.G. (1992). Temporal variation in point counts of birds in a lowland wet forest in
Costa Rica. Condor 94: 265―275.
Derlindati, E. J., & Caziani, S.M. (2005). Using canopy and understorey mist nets and point
counts to study bird assemblages in chaco forests. Wilson Bulletin. 117: 92―99.
Haselmayer, J. & Quinn, J.S. 2000. A comparison of point counts and sound recording as bird
survey methods in Amazonian Southeast Peru. Condor 102: 887-893.
Marsden, S.J. (1999) Estimation of parrot and hornbill densities using point count distance
sampling method. Ibis 141: 377–390.
Martin, T. E., Blackburn, G. A. & Simcox, W. (2010) An assessment of the effectiveness of two
methods in describing a neotropical cloud forest bird community. Ornithologica Neotropical, 21,
131-147.
Herzog, S.K., Kessler, M., & Cahill, T.M. (2002). Estimating species richness of tropical bird
communities from rapid assessment data. Auk 119: 749―769.
Howell, S.N.G. & Webb, S. (2005) A Guide to the Birds of Mexico and Northern Central
America. Oxford: Oxford University Press.
Karr, J.R. (1981). Surveying birds with mist nets. Studies in Avian Biology 6: 62―67.
Lynch, J.F. (1995). Effects of point-count duration, time of day, and Aural stimuli on
detectability of migratory and resident bird species in Quintana Roo, Mexico. Pp. 1―6 in
Ralph, C. J., J. R. Sauer, & S. Droege. (eds). Monitoring bird populations by point counts.
USDA Forest Service General Technical Report. US Department of Agriculture, Albany,
California.
MacArthur, R.H. & MacArthur, A.T. (1974). On the use of mist nets for population studies of
Birds. Proc. Nat. Acad. Sci. USA. 71: 3230―3233.
Remsen, J.V. (1994). Use and misuse of bird lists in community ecology and conservation. Auk
111: 225―227.
Remsen, J. V. & Good, D.A (1996). Misuse of data from mist net captures to assess relative
abundance in bird populations. Auk 113: 381―398.
Sberze1, M., Cohn-Haft, M. & Ferraz, G. (2010). Old growth and secondary forest site
occupancy by nocturnal birds in a neotropical landscape. Animal Conservation 13: 3-11.
Sekercioglu, C.H. 2010. The mystery of nocturnal birds in tropical secondary forests. Animal
Conservation 13: 12-13.
Sutherland, W. J., Newton, I, & Green, R.E. (2004). Bird ecology and conservation:
a handbook of techniques. Oxford University Press, Oxford, UK.
Thiollay, J. M. (1989). Censusing of diurnal raptors in a primary rain forest: comparative
methods and species detectability. Journal of Raptor Research. 23: 72-84.
Whitman, A. A., Hagan, J.M & Brokaw, N.V.L. (1997). A comparison of two bird survey
techniques used in a sub-tropical forest. Condor 99: 955―965.
Wunderle, J.M. (1994) Census Methods for Caribbean Land Birds. New Orleans: United States
Department of Agriculture.