Research pIan
Introduction
Purpose
This study aims to identify any correlation between distance to water and Northern Cardinal populations in McKinney Falls State Park, Austin, Texas.
Hypothesis
This study hypothesizes that the population of Northern Cardinals have a positive correlation with distance to water.
Background Information
The Northern Cardinal, or Cardinalis cardinalis, is a songbird that is known for its bright red plumage which occurs in its males. Other identifying features of the cardinal include a distinctive crest and black mask (Britannica). They also have a short and thick orange bill and a relatively long tail (Britannica). The bird’s numbers have grown by about 0.32% each year since 1966 (North American Breeding Bird Survey) to a current total population of approximately 130 million (Partners in Flight Databases). Their range has been expanding from the southern United States and Mexico to more parts of the U.S. (Scenic Hudson). Northern Cardinals have been found to exist in greater abundance in cities than in rural areas, highlighting the significance of this study. This is because invasive fruits such as the Amur Honeysuckle abound in cities and supply them with Vitamin C (Staengl, Ezra & Vondrasek, Joanna, 2024).
The invasive species near the creek should not present themselves as a possible dependent variable to additionally affect and correlate birds’ closeness to water, as no correlation has been found between location and the percentage of cardinalis’ diet consisting of invasive species. This ratio remains constant between urban and rural parks and likely remains constant between areas adjacent to bodies of water and areas distant from bodies of water (Staengl, Ezra & Vondrasek, Joanna, 2024).
There exist several subspecies within the Cardinalis genus and cardinalis species, which are spread throughout North America. The subspecies cardinalis is the focus of this study and is found throughout the eastern United States and most of Mexico, with a range stretching along its gulf until the Yucatan Peninsula and as far inland as Chihuahua (Smith et al., 2011).
This same subspecies is omnivorous, feeding on mainly plants during the winter and insects during the breeding season. Its lack of migration means it must be able to find and digest a range of food sources (Staengl, Ezra & Vondrasek, Joanna, 2024). This may distribute the population of Cardinalis cardinalis cardinalis throughout a geographic region as individual birds avoid each other’s competition. Within the area of this study, however, the water-adjacent areas can be clearly ecologically distinguished from those farther away from water. Additionally, water has the effect of supporting insects and plants and increasing their populations.
Emberizoids like the Northern Cardinal have been found to be cognitively advanced and adept at colonizing new areas and then growing in population (Lefebvre, et al, 2016). From this it is inferred that the bird of this study’s focus should be an opportunistic species able to take advantage of varying landscapes and water availability. This equalizing factor may contribute to similar population densities of Northern Cardinals between water-adjacent areas and non-water-adjacent areas.
Now, the total geographic range of the Northern Cardinal species is from southern areas of the coast of the Gulf of Mexico to the Eastern coast and Northern border of the United States. The range goes as far west as Southern Arizona, Northern Mexico, and most of Texas. The Northern Cardinal's preferred habitat is “backyards, parks, woodlots, and shrubby forest edges” (All About Birds). Northern Cardinals like to sit low in shrubs and trees where they can forage near or on the ground. They are also known for traveling in pairs (All About Birds). The Northern Cardinal has a melodious song that people identify by the mnemonic, “birdie, birdie, birdie”. Their call is a loud, metallic chip sound (All About Birds).
It has been found that Cardinals have a higher density of population near riparian vegetation (Dow, 1970). Riparian vegetation is on wetlands or near banks of rivers, showing that Northern Cardinals are more likely to inhabit areas close to water. According to the study, rivers can act as guidelines when cardinals disperse from the nest they were born in. Because of this many individual birds will end up close to rivers when they create their nests, making their population higher in riverside areas. The sedentary nature of cardinals implies that despite natal dispersal of a few hundred feet, they should remain around these riparian areas.
Site Description
Location
McKinney Falls is located in southeast Austin 4.9 kilometers west of the southernmost point of the Austin-Bergstrom International Airport (Google).
Size and Shape
The area of McKinney Falls State Park is 259.40 hectares (Visit Austin). The park is shaped similarly to a vertically aligned rectangle.
Topography
The maximum elevation of McKinney Falls State Park is 199 meters. The minimum elevation of the park is 143.26 meters (Peakbagger). The park is generally flat but slopes towards Onion Creek. The slope is steepest within 30 meters of elevation of the creek, and becomes more gradual radially from it.
Geology
McKinney Falls State Park covers a diverse strip of land in Central Texas.
The area of the park is almost completely dominated by the Ko geologic layer, which is the geologic code for the Ozan Formation (USGS). The Ozan Formation is a Gulfian preserver that runs as far east as Arkansas, and is thicker in the Austin area, with about 600 feet of thickness. It makes contact with the younger Annona chalk layer and is primarily composed of clay and marl basally and quartz, calcite, glauconite, phosphate, hematite and pyrite more upward (USGS).
Several fossils have been found on the grounds of the park, including many inoceramids, a saltwater clam, which became extinct in the Cretaceous Period (Raney, 1997). This is evidence for the Western Interior Seaway that covered Central Texas from the Cretaceous Period to the Paleogene (Marfa Public Radio).
Areal Extent and General Type of Vegetation
The park is almost entirely wooded, likely 90%. The remainder of the land is almost equally grassland and the creek itself, roughly 5% each. One prevalent plant species that can be found in the area is the Bald Cypress, found lining the creek itself. Other plant species that can be easily found within McKinney falls are Ashe Juniper and Live Oak.
Availability of Water
Onion Creek, a tributary stream of the Colorado River, runs through the west side of the park flowing northeast (Texas State Historical Association). The level of flow within the park is high and large amounts of water can be seen flowing quickly through and over the rock formations (Field visit 2/16/25). A tributary stream of Onion creek, Williamson Creek, branches off towards the central western border of McKinney falls, running along the north western edge, leaving the park.
Proximity to Urban or Industrial Areas
Located in the urban area of Austin, Texas, McKinney Falls State Park is surrounded by proximal human settlement. A golf course is adjacent to the bend of the creek, which demarcates the westernmost border of the park (Google).
History
McKinney Falls State Park was first acquired by the City of Austin in 1971 (Austin City Records). The area has been in use since the 18th century, causing indentations in the rock (National Park Service). It was first used as a ranch by a number of landed men in the area, and eventually fully developed by Thomas Freeman McKinney, who ranched and bred horses there.
In 2013, a flood damaged 1,200 homes near the creek and inundated the bathrooms and visitor’s center with water (Garrett, 2015).
Research Plan
Design of Study
Lengths:
Orange (Owen): 1147.65 meters
Purple (David): 947.59 meters
Yellow (Ellington): 899.41 meters
The percentage of the total study area from which data will be collected is 28.86%.
This study aims to discern the relationship between Northern Cardinal populations and large bodies of water. The three transects covered here are of varying distances from a major body of water, to which they are all mostly parallel. This means that the transects should vary in Northern Cardinal populations depending on how far they are to water.
The northernmost transect runs along a trail directly adjacent to Onion Creek, an approximately 20-meter-diameter river (Google). This trail is within 10 meters of the creek, ideal for observing and recording the population of cardinals closest to bodies of water. Additionally, the trail is surrounded by trees that do not obstruct vision, which aids in identifying birds.
500 meters south of this transect is the middle transect in terms of latitude. This transect runs from the northernmost point of the Picnic Trail’s parking lot to the path to the Youth Group Campsite, ranging from within 110 meters of the water to more than 400 meters from it. The vegetation cover is clear along the transect due to the transect being along a road which is then interrupted by densely wooded vegetation.
The southernmost transect runs from the southernmost turn of the Onion creek trail to its northernmost end, ending at the campground loop road. The vegetation cover is dense wooded area. This trail is 575 meters away from water on the northernmost end and 700 meters from water at the southernmost end.
Materials
Field journals (Unison)
Binoculars (Bushnell)
Merlin Bird ID (Cornell Lab)
Procedure
3 Transects within 200 meters of 1 kilometer established at varying distances from water source.
Transects surveyed 6 times over different weeks.
Surveyors will walk at 1 km/hr for the length of the transect and record every instance of Northern Cardinal either seen or heard by call or song. Surveyors will record every Northern Cardinal once by the way they first observed the Northern Cardinal at the distance the Northern cardinal is from them, marked on a sheet with sections in 5 meter increments going to 35 meters, then moving in 30 meter increments to 125 meters.
The total amount of Northern Cardinals of every transect added up to create a total for that transect.
The amount of Northern Cardinals on either transect are compared to find which transect have a greater amount of Northern Cardinals.
Respective full detection strips will be created for each transect visit by finding a drop of 20% from the average of all previous 5 meter sections to the next.
Population estimate will be calculated by
Coefficient of detection is determined by dividing the total calculated population within the 125 meter area around the 1 km transect by the number of total Northern Cardinals detected by surveyor.
A correlation or lack thereof between Northern Cardinal populations and distance to water is identified.
Annotated Bibliography
Smith, Brian, et al. “The role of historical and contemporary processes on phylogeographic structure and genetic diversity in the Northern Cardinal, Cardinalis cardinalis.” https://www.biomedcentral.com/, Springer Nature, https://bmcecolevol.biomedcentral.com/articles/10.1186/1471-2148-11-136.
This paper discusses the genetic diversity of different Northern Cardinal subpopulations. It finds that the Northern Cardinal subpopulation throughout the central and eastern United States is the cardinalis subspecies, allowing inference from this mitochondrial lineage (implying a cardinalis mitochondrial Eve) that other articles on Northern Cardinals in the United States will cover the same subspecies of genetic similarity. This eliminates the possibility of this study being misinformed by articles covering separate subspecies.
Staengl, Ezra & Vondrasek, Joanna. “Winter Diet of the Northern Cardinal (Cardinalis cardinalis) in Central Virginia: A Comparison of a Rural and an Urban Site.” researchgate.net, The Raven Vol. 95,
This paper is an in-depth analysis of the diet of Northern Cardinals, with a focus on the variation of diet between rural and urban parks. Although the original hypothesis that urban cardinalis ate more non-native plants by percentage of diet than rural cardinalis was proved incorrect, the study developed critical ideas concerning the seasonal diet of Northern Cardinals. Most notably, the cardinals were found to consume diets of 30% non-native foods, which has further implications about the reliance of Northern Cardinals on native species. Further, separate study must be held on the percentage of invasive plant cover in the LASA Preserve and the effects it may have on Northern Cardinal population to understand how this would affect total population of cardinalis throughout the park. Such an analysis is out of the scope of this study. By cross-referencing this study with that from Springer Nature, it is found that the subspecies analyzed here is the same subspecies observed at LASA Preserve.
Lefebvre, Louis, et al. “Feeding innovations in a nested phylogeny of Neotropical passerines.” https://royalsociety.org/journals/, The Royal Society, https://royalsocietypublishing.org/doi/full/10.1098/rstb.2015.0188
This study of the Emberizoid class of birds, in which the family Cardinalidae is classified, shines light on the adept colonization birds such as the cardinals have performed. Northern Cardinals are common birds throughout much of the northern New World. This success points to Northern Cardinals being highly adaptable and possessing a varied diet of diverse species.
Dow, Douglas D. “Distribution and Dispersal of the Cardinal, Richmondena Cardinalis, in Relation to Vegetational Cover and River Systems.” The American Midland Naturalist, vol. 84, no. 1, 1970, pp. 198–207. JSTOR, https://doi.org/10.2307/2423736. Accessed 13 Feb. 2025.
This study of Northern Cardinal dispersal showed where Cardinals are most likely to end up after breeding dispersal. This gives reasonable data to say that cardinalis distribution has a positive correlation to the presence of bodies of water, specifically river systems and similar waterways. The conclusion of this study greatly influenced the hypothesis of this study, which was tested.
“Northern Cardinal | Bird | Britannica.” Www.britannica.com, 31 Jan. 2025, www.britannica.com/animal/northern-cardinal.
This online resource describes cardinals’ phenotypic characteristics. It was used to describe specific physical information which would have been difficult or impossible to include in such detail solely from observation.
“Northern Cardinal Identification, All about Birds, Cornell Lab of Ornithology.” Allaboutbirds.org, 2017, www.allaboutbirds.org/guide/Northern_Cardinal/id.
This webpage provided critical information concerning the geographical distribution and common habits of the bird of this study’s focus, the Northern Cardinal.
Guest Blogger. “Exploring McKinney Falls in Austin.” austintexas.org, Visit Austin, 2024 https://www.austintexas.org/austin-insider-blog/post/mckinney-falls/#:~:text=With%20641%20acres%20and%2081,fishing%2C%20and%20mountain%20biking%20trails.
This blog article provided the acreage of the park that is the focus of this study. It also detailed human activity that takes place within the park, a crucial piece of information for the purposes of this study.
“Pocket Texas Geology.” https://www.usgs.gov/, United States Department of the Interior, https://webapps.usgs.gov/txgeology/.
This interactive website revealed the underlying geological formations covering the park in which this study’s data was collected.
“McKinney Falls State Park High Point, Texas.” https://www.peakbagger.com/Default.aspx, Peakbagger, https://www.peakbagger.com/Peak.aspx?pid=-53846#:~:text=653%20feet%2C%20199%20meters
This is a profile of McKinney Falls’ topography and offers a maximum elevation. It also allows for minimum elevation to be calculated through the topographic map embedded within the site.
“Data & Results.” www.pwrc.usgs.gov/bbs/, 2021,
https://www.pwrc.usgs.gov/bbs/results/.
This is the official website of a survey group, the North American Breeding Bird Survey. It contains data of recorded bird populations since 1966, offering statistical information on changes in their populations since then. These data include counts of the Northern Cardinal.
“McKinney Falls State Park.” https://www.nps.gov/index.htm, National Park Service, https://www.nps.gov/elte/learn/photosmultimedia/mckinney-falls-state-park.htm
This source gives information about early McKinney falls history, including the first recordings of McKinney falls by Isidro Félix Esty Espinosa and how it has evidence of Native Americans and early Americans using the area as a trail.
Texas. “Onion Creek (Blanco County).” Texas State Historical Association, 2025, www.tshaonline.org/handbook/entries/onion-creek-blanco-county.
This site provided the basic history of the study area.
Raney, Jay. “Down to Earth at McKinney Falls State Park, Texas.” Utexas.edu, 2025, store.beg.utexas.edu/de/291-de0001.html. Accessed 1 Mar. 2025.
This book provided for more in-depth geologic history of McKinney Falls.
James, Jurassic. “Llano Uplift: Geology of the Texas Hill Country | Jurassic James.” Jurassicjames.com, 2018, jurassicjames.com/geology-of-the-texas-hill-country/. Accessed 1 Mar. 2025.
This source offered information on some geologic phenomena observable at McKinney Falls today.
“Western Interior Seaway.” Marfa Public Radio, Radio for a Wide Range., www.marfapublicradio.org/show/nature-notes/2015-06-08/western-interior-seaway.
This source gave clear and concise information about the ancient geology of Central Texas.
Garrett, Stephen. “Park Pick: After the Flood.” Texas Parks and Wildlife, 2015, https://tpwmagazine.com/archive/2015/jan/scout4_parkpick_mckinneyfalls/
This article offered a reliable retelling of the flooding event that occurred in McKinney Falls in 2013.