1. TRENDS IN AVIAN POINT COUNT DATA IN RED BUTTE CANYON FROM 1991­2014
Kylynn Parker and Jordan Herman
Jordan Herman​1​
, Mark Leppert, PhD​1​
, Sherwood Casjens, PhD​1​
, Cagan Sekercioglu, PhD​1
Department of Biology
1​
University of Utah
201 Presidents Circle, Rm. 201, Salt Lake City, UT, 84112
Introduction
Red Butte Canyon (RBC) is a Research Natural Area administered by the US Forest Service in Salt Lake City,
Utah. RBC is an undisturbed area and a haven for the 144 avian species that have been recorded there to date. Red
Butte Canyon rests in the Pacific Flyway of western North America which is a major migratory corridor for migrating birds.
While migrants and over­wintering birds are monitored in the canyon throughout the year, the analysis of point count data
presented in this paper will focus exclusively on breeding birds in RBC. The aim of this paper is to determine if there are
notable trends in breeding bird point count data in the area over the past 22 years. Our research questions are: has the
relative abundance of the top five most commonly detected avian species in Red Butte Canyon notably changed through
space and time in two transects? How do the count trends compare from 1991­2014? This project is just the beginning of
raw point count data that can be analyzed for current and future projects.
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2. Methods
Point count data were collected by Mark Leppert, PhD and Sherwood Casjens, PhD of the University of Utah. The
number of bird species that were both seen and heard were recorded in 10 different transects within RBC over the past 22
years (1991­2014), yielding a total of 457 survey
days. In 2013 and 2014, the data were compiled and
entered into a database. In this paper, we analyze
count data from transect 1 and transect 3 which had
the highest survey efforts of the ten transects we
focused on (Figure 1) and included only the top five
most commonly detected species in both transects.
These species are the Black­Capped Chickadee
(​Poecile atricapillus), Warbling Vireo (​Vireo gilvus​ ),
Yellow Warbler (​Dendroica petechia​ ), Spotted
Towhee (​Pipilo maculatus), and Lazuli Bunting
(​Passerina amoena). Detection trends were found by
graphing the number of individual birds seen or heard in transect 1 and 3 over the days since surveys began in 1991
(Bled et al. 2013).
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3. Observer surveys were conducted at random periods throughout the year and there were no pre­determined
controls. In order for this project to continue and to record as much pre­controlled data as possible it is necessary to get a
much more accurate representation of changes in bird populations in RBC over time. The data were controlled for
transect (1 and 3), number of observers (two), season (April­May), and time of day (all surveys that began before noon).
To obtain a more accurate understanding of the abundance of these birds in each transect over the past 22 years, the
breeding months of April and May were chosen as the focus of the analysis and only observations made during surveys
that ended before noon on each day were included.
Results
The following charts show the individual count trends of the top five bird species detected between transect 1 and
transect 3 from 1991­2014. Results are shown in figure 2 and figure 3. The graphs in figures 2 and 3 present varying
trends in the months of April and May over the years. It is interesting to see that some of the trends shown follow similar
trajectories.
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4.
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5.
Discussion
The trends in figures 2 and 3 indicate that the relative abundance of the top five most commonly detected species
in RBC vary over time during the months of April and May (the breeding season) of each year relative to each other. It is
interesting to see that trends of certain species follow similar paths, possibly indicating that these species require similar
ecological niches and their trends are tracking changes in the niche. For example, the Yellow warbler and Warbling vireo
data in figure 3 show very similar trends. According to the Handbook of the Birds of the World (del Hoyo et al. 2015),
Warbling vireos spend the majority of their time foraging for insects and breeding in deciduous woodland habitats along
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6. forest edges, roadsides, and suburban areas. Yellow warblers generally breed in damp habitats and feed on insects and
some berries. Red Butte Canyon is primarily a riparian habitat which has a combination of deciduous woodland and damp
habitats which may be an explanation as to why we see such similar detection trends between the two species, but further
observations and analysis is required in order to form a serious hypothesis.
It is important to note that in transect 3 (figure 3) there is a decreasing trend in detection of the Yellow warbler and
the Warbling vireo. There could be many reasons as to why we see this trend, but it could simply be that more individuals
of those populations are breeding elsewhere in the canyon. In other words, it is not an accurate representation of their
population sizes. In order to get a more authentic representation it is necessary to compare these species populations to
trends found in other transects of the canyon. However, according to Robbins et al. 1989, there has been a significant
decline in population size of Neotropical Migrants, or birds that migrate between North and Central America. We see the
same trend of Yellow Warblers and Warbling Vireos in the above graphs. Another alternative hypothesis to the changes
we see in figure 2 and 3 could be due to forest fragmentation and city development throughout the western United States
which may cause breeding and migration success to decline as a result (Peterjohn and Sauer, 1994).
Another potential reason as to why there is often much correlation between species of similar natural histories
could be because Red Butte Canyon lies in the Pacific Coast Highway, a major corridor for migrating birds. RBC is a
popular place for migrating birds to refuel during their long journey across the continent in search of more suitable
environments as the season changes. With 144 species of birds migrating through the same area, there is high likelihood
that individual birds of similar species are competing for the same resources.
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7.
Future Directions
More extensive statistical analysis of the data is needed to understand how bird populations are changing over the
years in Red Butte Canyon.
The LOESS regression analysis method offers a useful control that should be implemented in the collected data.
To prevent the same group of individuals from being counted more than once this method will control for observer effects
on the data (Link and Sauer, 1998). This will be done by comparing controlled and uncontrolled count data to get an
accurate estimate of population size without major observer effects causing inaccurate representation of the data (James
et al. 1996).
While it is not possible to get a perfectly accurate measurement of avian species population trends via point count
data of population changes due to observers effects in RBC, it is still enough information to find trends in the avian
community in this area over the years (Link and Sauer, 1997). Research is never ending and this project is of no
exception. In order to continue detecting trends of bird populations in Red Butte Canyon and to estimate population
change trajectory (future population change) it is absolutely necessary to continue observations in the canyon, specifically
with pre­determined controls for the observers to use when surveying the canyon.
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8. References
Bled F, Sauer J, Pardieck K, Doherty P, Royle JA. “Modeling trends from North American breeding survey data: a spatially
explicit approach.” 2013. PLos ONE. Vol 8(12).
del Hoyo J, Elliott A, Sargatal J, Christie DA, de Juana E. (eds.) “​Handbook of the Birds of the World Alive.” 2015. ​Lynx
Edicions, Barcelona. Retrieved from http://www.hbw.com/ on 09/10/2015.
James FC, McCulloch CE, and Wiedenfeld DA. “New approaches to the analysis of population trends in land birds.”
Ecology. 1996. Vol. 77, pp. 13­21.
Link WA and Sauer JR. “Estimation of population trajectories from count data.” 1997. ​Biometrics. Vol. 53(2), pp. 488­497.
Link WA and Sauer JR. “Seasonal components of avian population change: joint analysis of two large­scale monitoring
programs.” 2007. ​Ecology. Vol. 88(1), pp. 49­55.
Peterjohn BG and Sauer JR. “Population trends of woodland birds from the North American breeding survey.” 1994.
Wildlife Society Bulletin. Vol. 22(2), pp. 155­164.
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9. Robbins CS, Sauer JR, Greenberg RS, and Droege S. “Population declines in North American birds that migrate to the
neotropics.” 1989. ​Proceedings of the National Academy of Sciences of the United States of America. Vol. 86(19), pp.
7658­7662.
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