Date of Award
4-11-2023
Document Type
Thesis
Department
Biology
First Reader
Dr. Christin Pruett
Second Reader
Dr. Sharon Hamilton
Third Reader
Dr. Jay Curlin
Abstract
Since 1973, North America has lost 2.9 billion birds due to habitat loss and fragmentation. To assess the effects of habitat complexity on bird diversity and abundance, 96 locations were surveyed at Jack Mountain Wildlife Management Area (WMA) using ten-minute point counts. All birds seen and heard at each point were documented, and habitat complexity was assessed by examining the percentage of ground coverage, shrub coverage, midstory tree layer, and canopy coverage at each point. A habitat complexity index was generated from these plant surveys. Previous research at Jack Mountain has shown that habitats dominated by pine trees had the highest bird species diversity and abundance in comparison to mixed or deciduous woodlands. Habitat complexity has been associated with an increase in bird species diversity, and thus, we hypothesized that pine habitats would have greater habitat complexity and that habitat complexity would be positively correlated with bird diversity and abundance.
Statistical tests were performed in R to assess these hypotheses. In comparisons between species abundance or diversity with the habitat complexity index, no significant correlations were observed. We then compared each of the four aspects of the habitat complexity index with species diversity and abundance, using a multivariate model, and found a significant negative correlation between species abundance and diversity versus canopy coverage. Additionally, significant positive correlations were found between species abundance and species diversity versus ground cover and species abundance and diversity versus shrub coverage. Each point location was assigned to a habitat class based on the percentage of pine and deciduous tree cover. As found in previous summers by students at Ouachita Baptist University, a comparison among habitat classes and species diversity showed higher numbers of species in pine habitats, however, the habitat complexity index did not differ among habitat classes. To further evaluate, the abundance of birds in pine habitats, aspects of the habitat index were then compared to the habitat classes. We found smaller amounts of canopy coverage and larger amounts of ground cover and shrub cover in pine habitats than in deciduous or mixed habitats.
The most common bird species inhabiting Jack Mountain WMA are insectivores, and thus, they rely primarily on insects as their food source. Therefore, insect abundance was assessed at chosen point locations for both pine and deciduous forests to assess whether habitat complexity or habitat class were drivers of insect abundance and if insect abundance was positively correlated with bird abundance and diversity. Comparisons of the habitat complexity index and insect abundance supported that the two were not correlated. Similarly, associations between the habitat classes and insect abundance were not associated. Additionally, species abundance and diversity were not found to be correlated with the presence of insects either. Canopy coverage was also compared to insect abundance, and a correlation was not observed. Since associations were not found with insect presence, it was concluded that other habitat variables are responsible for bird richness.
These findings suggest that there are more bird species and individuals among pine habitats at Jack Mountain because of less canopy coverage. Areas with higher canopy and midstory coverage on average had a smaller number of birds present, and areas with higher ground and shrub coverage had a larger number of birds present. A reduction in canopy coverage in pine habitats could lead to an increase in ground and shrub coverage, which are both correlated with an increase in the diversity and abundance of birds. In conclusion, we reject our initial hypothesis about bird diversity and pine habitat's being associated with increasing habitat complexity. Our findings suggest that the population dynamics of birds at Jack Mountain are associated with a diverse set of habitat variables that cannot be simplified into a single habitat complexity index.
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This work is licensed under a Creative Commons Attribution-NonCommercial-No Derivative Works 4.0 International License.
Recommended Citation
Tidwell, Grace, "Bird Diversity and Abundance in Relation to Habitat Complexity at Jack Mountain Wildlife Management Area" (2023). Honors Theses. 905.
https://scholarlycommons.obu.edu/honors_theses/905