Theses and Dissertations

Issuing Body

Mississippi State University

Advisor

Wang, Guiming

Committee Member

Kouba, Andrew J.

Committee Member

Burger, Leslie, M.

Committee Member

Burger, Loren, W.

Committee Member

Colvin, Michael E.

Date of Degree

12-13-2024

Original embargo terms

Visible MSU only 2 years

Document Type

Dissertation - Campus Access Only

Major

Forest Resources (Wildlife, Fisheries & Aquaculture)

Degree Name

Doctor of Philosophy (Ph.D.)

College

College of Forest Resources

Department

Department of Wildlife, Fisheries and Aquaculture

Abstract

Avian populations have undergone global declines that have profound implications for biodiversity. The prognosis of avian decline risks has been hindered by a lack of understanding of the endogenous and exogenous determinants of avian fauna declines. I investigated the spatiotemporal population dynamics of 428 North American breeding birds using the Breeding Bird Survey data from 1970 to 2018. I hypothesized life history strategies would determine avian population trends by mediating population regulation and responses to global climate changes (H1). I also hypothesized birds with increasing or stable population trends would have greater within-species spatial variability in their population responses to local climate changes and abundances than species with decreasing trends (H2). Machine learning methods classified 225 species (53%) to a decreasing group and 203 species (47%) to an increasing group. The effects of North Atlantic Oscillation (NAO) and Southern Oscillation (SO) on continentally aggregated populations were significantly greater in the increasing group than the decreasing group. However, neither direct nor delayed density dependence differed between the two groups. Bayesian phylogenetic logistic regression demonstrated that increased fledging age significantly reduced avian population decline risks, suggesting that increased investments of parental care mitigate avian population decline risks. Birds living in open areas had about 50% higher risks of population declines than those associated with densely vegetated ecosystems, signaling alarming avian faunal decline risks caused by converting grasslands and shrublands to agriculture or other land use. Structural equation models demonstrated that life history strategy was a direct causal factor of density dependence and population responses to NAO and SO and an indirect cause of avian population decline via mediating avian responses to SO, supporting H1. In metapopulations of 159 breeding birds from 1985 to 2018, density dependence did not differ significantly between the decreasing and increasing groups; however, bird species in the increasing group had greater within-species spatial variance in population responses to temperature and precipitation than declining species, partially supporting H2. Global changes may homogenize avian life history traits and population responses to climate changes, which in turn increase avian fauna decline risks.

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