Emergent Insect and Neotropical Migratory Bird Interactions and Responses to Habitat, Hydrology, and Progressive Urbanization In

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11-2-2015 Emergent Insect and Neotropical Migratory Bird Interactions and Responses to Habitat, Hydrology, and Progressive Urbanization in the Tampa Bay Region Nathaniel Lee Goddard University of South Florida, [email protected]

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Emergent Insect and Neotropical Migratory Bird Interactions and Responses to

Habitat, Hydrology, and Progressive Urbanization in the Tampa Bay Region

Nathaniel Lee Goddard

A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy Department of Integrative Biology with a concentration in Ecology College of Arts and Sciences University of South Florida

Major Professor: Thomas L. Crisman, Ph.D. David Lewis, Ph.D. Peter Stiling, Ph.D. Mark Rains, Ph.D.

Date of Approval: October 30, 2015

Keywords: Emergent Insects, Wetlands, Urbanization, Groundwater Pumping, Subtropics,

DEDICATION

I would like to dedicate this dissertation to Passerina ciris, the Painted Bunting. It was the chance occurrence of a male painted bunting landing at a puddle in the center of a rural Arkansas dirt road on a summer day in the early 1970’s that led to this dissertation. My father who at the time was a young Arkansas country boy beginning college was driving home from school down that road on that very day and came across a bird so bright and beautiful that he was sure there was no way that it was native. He didn’t know what to make of it since he had never encountered a bird with such beauty and colors. Upon returning to school the following week and asked his professor what it could have been, and he was shown a bird book and informed of the species. It was that chance encounter that began a lifelong obsession for birding that has persisted to this very day. Some of my earliest memories include being woken up at 4:00 am to

‘help’ conduct breeding bird surveys. My father’s passion for birds filled my early memories with events such as hiking mountains in Colorado, Alaska, and Wyoming searching for the next new species, setting up spotting scopes on the beaches to pick out uncommon species of sandpipers and gulls that are virtually indistinguishable to the untrained eye. My father instilled his love for nature and a desire for conservation in me from a very young age and has molded me into the man I am today. So it is very likely that if it wouldn’t have been for that thirsty bunting at that faithful puddle on that day, this work may never have been done.

TABLE OF CONTENTS

List of Tables ...... iii

List of Figures ...... iv

Abstract ...... vi

Chapter One: General Introduction ...... 1 References ...... 7

Chapter Two: Responses of emerging insects in cypress dome wetlands of West Central Florida to groundwater pumping and urbanization ...... 9 Abstract ...... 9 Introduction ...... 10 Methods...... 15 Site Selection ...... 15 Hydrology ...... 16 Land Use ...... 16 Insect Sampling ...... 16 Data Analysis ...... 18 Results ...... 18 Summary Data ...... 18 Temporal Distribution ...... 19 Wellfield Insect Emergence ...... 20 Urbanization ...... 21 Discussion ...... 25 References ...... 29

Chapter Three: Relationships among wetland hydroperiod, insect seasonality, and Neotropical bird migrations in West Central Florida ...... 45 Abstract ...... 45 Introduction ...... 46 Methods...... 51 Study Sites ...... 51 Bird Surveys...... 52 Insect Surveys ...... 53 Analysis...... 54

Results ...... 55 Birds…...... 55 Insects and Hydrology ...... 56 Relationship between Birds and Insects ...... 59 Discussion ...... 60 References ...... 64

Chapter Four: Responses of forest dwelling migratory bird communities to progressive urbanization in West Central Florida ...... 78 Abstract ...... 78 Introduction ...... 79 Methods...... 84 Site Selection ...... 84 Land Use ...... 84 Bird Surveys...... 85 Insect Surveys ...... 85 Environmental Characterization ...... 86 Analysis...... 87 Results ...... 88 Urbanization ...... 90 Bird Trends with Urbanization ...... 91 Discussion ...... 94 Conclusions…...... 98 References ...... 100

Chapter Five: General Conclusions ...... 116 References ...... 122

Appendices ...... 125 Appendix A. Malaise Trap Adult Insect Data ...... 125 Appendix B. Aquatic Dipnet Survey Insect Data ...... 126 Appendix C. Insectivorous Bird Community ...... 128 Appendix D. Emergent Insect Community ...... 131

LIST OF TABLES

Table 2.1: Emergent insect counts both for important Dipteran Families and Genera and non-Dipterans Orders...... 37

Table 2.2: Shannon’s Diversity Models for Diptera and Non-dipteran insects...... 39

Table 3.1: Responses of bird guilds to emergent and adult insect abundances...... 71

Table 3.2: Structural Equation model of hydrology, Insects, and birds...... 71

Table 4.1: Environmental and biological factors associated with bird community in urban and rural environments...... 107

Table 4.2: Regression models of bird community responses to factors associated with urbanization...... 108

iii

LIST OF FIGURES

Fig. 2.1: Map of cypress dome wetland study sites in the Northern Tampa Bay Region of Florida...... 40

Fig. 2.2: Mean annual rainfall for Hillsborough County FL, February 2012 through January 2014...... 41

Fig. 2.3: Insect communities compared monthly with water level ...... 41

Fig. 2.4: Insect emergence plotted against the number of month wetland has been inundated...... 42

Fig. 2.5: Average predatory insects abundance per square meter ...... 42

Fig. 2.6: Shannon diversity index for insect Order and Family ...... 43

Fig. 2.7: Monthly emergence rates for Chironomidae Genera ...... 44

Fig. 3.1: Temporal trends in the abundance of insectivorous bird populations...... 72

Fig. 3.2: Insectivore communities by Migratory Strategy...... 73

Fig. 3.3: The relationship between rainfall, water level and insect emergence in cypres wetlands...... 74

Fig. 3.4: Mean water level of wetland groups based on annual hydroperiod...... 74

Fig. 3.5: Insect emergence differences between study years...... 75

Fig. 3.6: Insect annual emergence versus length of inundation period by year of study...... 75

Fig. 3.7: Winter migratory bird abundance (Y-axis) plotted against relative abundance of adult insects...... 76

Fig. 3.8: Community abundance of migratory birds over the 2 year study period ...... 76

Fig. 3.9: Structural equation mode diagram of hydrology, insects, and birds...... 77

Fig. 4.1: Seasonal Distribution of bird migratory guilds ...... 109

Fig. 4.2: Average birds observed each year by site combined by site group...... 110

Fig. 4.3: Bird migratory guild annual abundance versus forest, urban, and light...... 111

Fig. 4.4: Insect emergence calculated annually...... 112

Fig. 4.5: Distance based redundancy analysis of bird community abundance matrices...... 113

Fig. 4.6: Dendrogram indicating site resemblance relative to wetland bird communities ...... 114

Fig. 4.7: Species richness similarity matrices for urban and rural sites plotted against bird communities...... 115

ABSTRACT

The growing human population threatens the many of the earth’s biological systems. In the last 600 years extinction rates risen from 1 extinction per million species per year (E/MSY) in the 1400’s to 50 E/MSY today. During this time period 1.5% of all known birds have gone extinct, because they could not adapt quickly enough to human mediated changes. The goal of this dissertation was to determine how urbanization and anthropogenic services needed to support urban areas impact cypress dome wetland aquatic insect and migratory bird populations that depend on them. In Central Florida cypress dome hydroperiods are driven by seasonal rainfall conditions and fill June and July with the onset of the Florida rainy season then begin drying beginning in October with the onset of the dry season. Some wetlands were strongly influenced by groundwater pumping and dried out quicker than others, a characteristic that reduced annual insect emergence. Decreased adult insect populations were associated with lower emergence rates early in the dry season led to lower utilization by insectivorous birds.

Winter migratory birds significantly related with adult insect abundance during winter months (r

= 0.578, p=0.049), and utilized this region at the peak in adult insect populations. Conversely,

Neotropical migrants travel through the region during spring when insects are scarce, and adult insects began sharp decline suggesting that Neotropical migrants depleted populations possibly leading to interspecies competition. Neotropical migrants strongly avoided urban areas and declined by 70% in urban areas, which may contribute to declining Neotropical migratory bird populations as a lack in adequate stopover sites may limit entire species. If they are not able to

vi adapt foraging patterns that utilize urban areas in Central Florida where urban development is increasing rabidly populations may continue to decline.

vii

CHAPTER ONE

GENERAL INTRODUCTION

Since the 15th century and the Age of Discovery during which European nations sent out naval expeditions to claim new lands and exploit newly discovered resources, the Earth’s extinction rate has increased by fifty fold from an estimated pre-exploration rate of 1 extinction per million species per year (E/MSY) to around 50 E/MSY today (Pimm et al. 2006), which is the highest extinction rate in 65 million years when the Cretaceous–Paleogene extinction brought an end to the age of dinosaurs (Wilson 1988). Coincidentally the only relatives of theropod dinosaurs remaining today are the birds, and since European expansion an estimated

154 bird species have become extinct, which is over 1.5% of the world’s total bird population.

There is no doubt that human development has had lasting effects of the world that we live in today. The world’s population has increased from 1 billion people at the beginning of the

19th century to over 7 billion today (200 years). The population has also transitioned into a urban centric society with over 50% of the world’s population living in urban areas (Dahl 2000), and approximately 40% living coastally within 100 km of the coasts (Dahl 1990). Urban development negatively impacts native biological communities by replacing natural systems with urban landscapes that contain only remnant natural habits, typically left as parks for other human activities. Anthropogenic threats to native species and environments are not limited to urban

development but include the spread of exotic and invasive species that threaten native food webs, over exploitation of species, pollution, and degradation of natural habitats.

Urban footprints are not restricted to the metropolitan fringe, but include entire ex-urban regions for resources and support. To support large human densities, that can be as high as

20,000 people per square kilometer (Mumbai, India), the ecological footprint expands and include farming area (to feed the urban population), landfills (to get rid of waste), and possibly the most important, sources of potable water for the population. The United States has an estimated ecological footprint of one person per 2.29 hectares (Reese and Wackernagel 2008) which extrapolates to a human ecological impact of about 80% of the nation’s total land area.

Urban areas are direct physical threats to the ecology of adjacent areas because pollution and environmental degradation threaten adjoining systems. Astronomical light pollution is just one type of urban degradation and affects about 10% of the earth’s land area and about 40% of the population has no clear view of the night sky due to skyglow (Cinzano et al. 2001). This is of environmental concern because light pollution has been implicated as a threat to migratory birds, disrupting migratory patterns and luring them into dangerous encounters with manmade structures (Pimm et al. 2008).

The Tampa Bay Metropolitan area is a coastal urban area with a population estimated at over 4 million people, and has doubled in just 30 years. This increase has had environmental consequences to the region including an over extraction of ground water from coastal Pinellas

County which resulted in saltwater intrusion of the local aquifer. Following saltwater intrusion

Pinellas County moved its water extraction efforts inland to adjacent Pasco and Hillsborough counties, then when environmental degradation became apparent in those regions a comprehensive review of environmental practices was initiated (Regan 2003). Environmental

issues associated with the overexploitation of water resources in Pinellas, Pasco and

Hillsborough counties became famous regionally and was highlighted by the local media as the

Tampa Bay Water Wars. Environmental impacts included drops of local water tables that led to excessive drying of the surrounding areas including nearby wetlands (Sophocleous 2002).

Lower water tables impacted wetlands by decreasing hydroperiods, causing soil oxidation and subsidence, and stressing wetland vegetative communities that lead increased tree mortality

(forested wetlands) and encroachment by upland plant communities. Another problem with decreased water tables and hydroperiods that has not been addressed is the impact to aquatic insect communities by decreasing water residence time and shortening the time available for insects to complete aquatic life stages (Lynch et al. 2002).

In Central Florida wetlands, insect phenology depends on the regions distinct seasonal rainfall patterns. Florida has two well defined seasons, a rainy and dry season that run from June through October and November through May respectively. Seasonal rainfall patterns are important for wetland insect communities especially during the aquatic larval stages that require anywhere between two weeks and a 6 months (Merit and Cummings 1996), proceeding the shorter terrestrial adult phase that serves for reproduction and dispersal. Some larvae are able to survive wetland dry periods by burrowing in the soils (Leslie et al. 1997), but most cannot and disappear with declining hydroperiods (Batzer and Wissinger). Colonization rates vary among aquatic species with rapid colonizers such as Chironomidae and Culicidae arriving quickly at newly flooded sites, while others including Odonates and Ephemeropterans taking longer and requiring longer inundation periods to complete their annual life cycles. Wetland community richness increases over time because of continued colonization, and is highest in wetlands with

the longest inundation periods, that maintain regular dry-down periods to remove fish and other predators (Batzer and Wissinger 1996).

Wetlands and riparian zones are important for both aquatic insects and migratory birds that rely on them as a primary food source. Migratory birds show a positive relationship with increasing moisture gradients because as soil moisture declines, so does insect production and food availability (Smith 1977). Moisture is a useful tool in determining habitat suitability for

Neotropical migratory birds along their migration routes (Smith et al. 2010), and migrants occupying drier habitats during the non-breeding period show poorer physical conditions, decreased survival (Latta and Faaborg 2002, Marra and Holmes 2001), and require longer periods of time to recover from long migratory jumps and thereby delay migration (Moore and

Yong 1991). Food availability at key stopover sites is vital for migratory bird survival and food scarcity impacts migration which is a time of extremely high seasonal mortality, accounting for approximately 85% of annual mortality in migrating songbirds (Sillett and Holmes 2002).

The Tampa bay region is an important point on the Atlantic Flyway functioning as principal egress points for birds traveling to Central and South America. This means food availability is extremely important at this juncture, and since the majority of Neotropical migratory land birds are insectivorous. Insect availability is vital at this juncture during biannual migrations through the region and birds can lose up to 40% of their body weight in a single fight of up to 500 miles across the Gulf of Mexico (Moore and Kerlinger 1989).

Since Tampa Bay is located at a principle juncture that has become highly urbanized over the last century, remaining green spaces is a prime concern to migratory bird conservation. Birds are thought to select stopover sites based on the probability that they can procure the energetic requirements needed to continue on in the migration (Yong et al. 1998) and have been found to

strongly avoid urban spaces (Goddard 2010), instead choosing remaining green spaces for foraging habitats. Because the majority of the remaining large green spaces in the region are water management areas where groundwater pumping takes place, hydrological impact poses a secondary threat to migratory birds. Drawdown from groundwater pumping decreases annual hydroperiods of nearby wetlands and may pose a threat to the migratory birds that utilize them.

Impacted wetlands are likely to have reduced insect communities that could lead to a bottom up control on insectivorous migratory birds. A decrease in habitat quality and/or food availability at this juncture during bird migration could potentially function as a limiting factor for the entire migratory community. If adequate habitat and food resources are not available in the region during spring with the influx of migrants, during the end of the Florida dry season, then intraspecific and interspecific competition may cause the area to function as a geographic bottleneck limiting bird populations. This could disproportionately favor early migrants that are typically short-distance migrants and harm long distance Neotropical migratory birds.

The goal of the study was to determine if or how environmental impacts associated with anthropogenic activities impact cypress dome emergent insect community and seasonal assemblages. Aquatic insect communities associated with varying wetland hydroperiods were compared with migratory bird communities using rural wetlands. Finally, bird community responses to urbanization were addressed including land use, food availability, and urban light pollution.

This study took place in the Northern Tampa bay region focusing on the environmental responses of cypress dome wetlands and associated communities to urbanization and hydrological stress. Data were collected monthly for 2 years (February 2012 through January of

2014) and included 25 wetlands subdivided into 5 study groups. Three groups of wetlands were

located in municipal wellfields while the remaining two groups were distributed across urban areas of Carrolwood and North Tampa. The three wellfield groups included wetlands in J.B.

Starkey Wellfield, Cypress Creek Wellfield, and Morris Bridge Road Wellfield. Urban wetlands were divided into two groups, with one in more recent development (post 1990), and another in older development (pre 1990).

References

Batzer D.P. & Wissinger S.A. (1996). Ecology of insect communities in nontidal wetlands.

Annual Review of Entomology, 41, 75-100.

Cinzano, P., Falchi, F., & Elvidge, C. D. (2001). The first world atlas of the artificial night sky

brightness. Monthly Notices of the Royal Astronomical Society, 328(3), 689-707.

Dahl, T.E. (1990). Wetland losses in the United States: 1780’s to 1980’s. U.S. Fish and Wildlife

Service, Washington, D.C., USA. Retrieved from –

http://water.epa.gov/type/wetlands/vital_status.cfm

Dahl, T. E. (2000). Status and trends of wetlands in the conterminous United States 1986 to

1997. US Fish and Wildlife Service.

Latta, S. C., & Faaborg, J. (2002). Demographic and population responses of Cape May

Warblers wintering in multiple habitats. Ecology, 83(9), 2502-2515.

Leslie A.J., Crisman T.L., Prenger J.P. & Ewel K.C. (1997). Benthic macroinvertebrates of small

Florida pondcypress swamps and the influence of dry periods. Wetlands, 17, 447-455.

Marra, P. P., & Holmes, R. T. (2001). Consequences of dominance-mediated habitat segregation

in American Redstarts during the nonbreeding season. The Auk, 118(1), 92-104.

Moore, F., & Kerlinger, P. (1987). Stopover and fat deposition by North American wood-

warblers (Parulinae) following spring migration over the Gulf of Mexico. Oecologia,

74(1), 47-54.

Moore, F. R., & Yong, W. (1991). Evidence of food-based competition among passerine

migrants during stopover. Behavioral Ecology and Sociobiology, 28(2), 85-90.

Pimm, S., Raven, P., Peterson, A., Şekercioğlu, Ç. H., & Ehrlich, P. R. (2006). Human impacts

on the rates of recent, present, and future bird extinctions. Proceedings of the National

Academy of Sciences, 103(29), 10941-10946.

Rees, W., & Wackernagel, M. (2008). Urban ecological footprints: why cities cannot be

sustainable—and why they are a key to sustainability. In Urban Ecology (pp. 537-555).

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Regan, K. E. (2003). Balancing public water supply and adverse environmental impacts under

Florida water law: from water wars towards adaptive management. Journal of Land Use

& Environmental Law, 123-184.

Sillett, T. S., & Holmes, R. T. (2002). Variation in survivorship of a migratory songbird

throughout its annual cycle. Journal of Animal Ecology, 71(2), 296-308.

Smith, K. G. (1977). Distribution of summer birds along a forest moisture gradient in an Ozark

watershed. Ecology, 810-819.

Smith, J. A., Reitsma, L. R., & Marra, P. P. (2010). Moisture as a determinant of habitat quality

for a nonbreeding Neotropical migratory songbird. Ecology, 91(10), 2874-2882.

Sophocleous, M. (2002). Interactions between groundwater and surface water: the state of the

science. Hydrogeology journal, 10(1), 52-67.

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Washington, DC: National Academy Press.

Yong, W., Finch, D. M., Moore, F. R., & Kelly, J. F. (1998). Stopover ecology and habitat use of

migratory Wilson's Warblers. The Auk, 829-842.

CHAPTER TWO

RESPONSES OF EMERGING INSECTS IN CYPRESS DOME WETLANDS OF WEST

CENTRAL FLORIDA TO GROUNDWATER PUMPING AND URBANIZATION

Abstract

Urbanization changes landscape structure and heterogeneity, and alters hydrology and water chemistry of local wetlands. As urban populations increase, so does the demand for domestic water supplies. Most of municipal water needs in Tampa Bay are obtained through groundwater pumping, which lowers local water tables and alters the hydrology of adjacent wetlands. Emergent insect communities of cypress dome wetlands were surveyed to determine if urban landscape change and hydrological alteration impacted community structure and seasonality. Insect emergence was greatest from July to October during the rainy season. The emergent insect community was dominated by the Order Diptera, which accounting for 89% of total emergence, and the family Chironomidae that attributed 59% of observations. While wetlands were flooded (June through December), adult insect community richness increased steadily, and wetlands healthy wetlands with longer hydroperiods (9 and 11 months) had higher emergence rates and community richness, while impacted wetland that had shorter hydroperiods

(4 and 6 months) had the lowest rates and fewest insect groups. Annual insect emergence rates positively correlated with wetland hydroperiod in rural wetlands (Pearson’s r = 0.57, p = 0.02)

but showed no trend in urban wetlands. Urban wetlands witnessed a 45% decline in all non- dipteran species compared to rural wetlands, and an overall decline in adult insect abundance.

Insect communities are important food items for migratory birds that use these habitats and could be a controlling factor for sensitive bird species utilizing coastal freshwater wetlands to refuel during migration.

Introduction

Wetlands are biologically diverse ecosystems that contain approximately 6% of all recorded species, but occupy only 1-2% of global surface area (Hawksworth and Kalin-Arroyo

1995), or 4-6% of land area (Mitra et al. 2005). Insects are important components of wetland biota, accounting for 95% of invertebrates, as well as 80% of total animal biodiversity (Wilson

1999). In the continental United States, Florida has the most wetland area, which comprises 27% of its land area (Dahl 2005).

Aquatic insects occupy a wide range of niches in wetland food webs including decomposers, collector-gatherers, scrapers, and predators (Cummins and Klug 1979). Their life cycles typically pass through a long aquatic larval stage before becoming a short lived terrestrial adult (Resh 1979, Butler 1984, Merritt and Cummins 1996). Metamorphosis into winged adults, also known as emergence, occurs at the water’s surface and facilitates dispersal and breeding

(Borror et al. 1989, Petersen et al. 2004). Adults of most taxa only return to water to deposit eggs (Merritt and Cummins 1996), with the exception of the orders Coleoptera and Hemiptera, which can return as adults to become the dominant predators of small isolated wetland communities (Stevens and Polhemus 2008).

Strategies for emergence vary both among and within aquatic insect groups. Emergence can be multivoltine (Morgan and Waddell 1961) or highly synchronized with a single massive emergence (Corbet 1964). Emergence periods are important foraging events for many insectivorous species and function to export energy from aquatic to terrestrial food webs

(Jackson and Fisher 1986). These events are so important that many bird species time migration and nesting specifically to coincide with them, including the migration of the California gull

(Larus californicus) to alkali lakes of the western U.S. to feed on brine flies (Ephydridae)

(Mahoney and Jehl 1985) and warblers, whose northward migration and nesting coincide with

Chironomidae emergence from Neartic lakes (Smith et al. 2007).

Aerial dispersal connects metacommunities and facilitates genetic flow (Bilton et al.

2001) among ephemeral wetlands and enables source populations to reseed communities extirpated during dry seasons (Batzer and Wissinger 1996). Winged dispersal is also adventitious in urban areas because it allows movement across environmental barriers such as highways and the built environment that limit dispersal of terrestrial organisms. Factors that influence recolonization by aquatic insects include distance to nearest water body and surrounding land use (Miller et al. 2002).

Cypress domes, a common forested swamp of the southeastern US, are favorable habitats for many aquatic insects because seasonal drawdown and often total desiccation can eliminate predatory fish (Batzer and Resh 1992). Invertebrates persisting in ephemeral wetlands must adapt to predictable drawdown events by either migrating to and from wetlands or surviving in place. Many avoid desiccation by either vertically migrating in wetland soils to follow the moisture gradient (Leslie et al. 1997) or estivating as desiccation resistant life stages (Williams

1996).

Once wetlands re-flood, invertebrate communities can rapidly revive and/or recolonize

(de Szalay and Resh 2000). Species able to persist in dry wetlands often display rapid emergence of adult insects upon re-flooding, with peak abundance during the first two months before declining as additional colonizing species increase competition and predation (Lake et al. 1989). Emerging insect communities are also strongly influenced by landscape spatial components including local distribution of freshwater habitats (wetlands, lakes, and streams), forest cover, and urban area. Landscape factors along with local wetland conditions (depth, hydroperiod, and water chemistry) (Batzer and Wissinger 1996) play an important role in community composition (Carling et al. 2013).

Forested wetlands like cypress domes can have a high degree of canopy coverage, typically greater than 90% during summer months. This leads to low light penetration to the water surface, which, when combined with tanic water color from humic acids and decomposition of organic soils, results in reduced aquatic primary production, low dissolved oxygen and acidic pH between 4.5 and 5.0 (Spangler 1984). Only the most tolerant insect species persist in such conditions, and diversity in forested wetlands tends to be lower than herbaceous wetlands regionally because of loss of sensitive taxa (Streever et al. 1995).

One group that has managed not only to overcome the harsh environmental conditions in wetlands but thrive is the Order Diptera. Dipterans are the most prolific aquatic insects in forested wetlands (Stagliano et al. 1998), with many possessing special adaptations including long breathing spiracles (Dilochopodidae), high levels of hemoglobin (Chironomidae), and vertical migration for surface breathing (Culicidae) (Connolly 2004). In the southeastern United

States, the family Chironomidae accounts for greater than 50% of total insects emerging from

wetlands (Leeper and Taylor 1998); other important dipteran families include Dilochopodidae,

Culicidae, Chaoboridae, and Simulidae.

Hydrology plays an important role in population dynamics of aquatic insect communities

(Bunn and Arthington 2002). Hydroperiod influences community structure (Layton and Voshell

1991), population densities, and community successional state (Fisher et al. 1982). Longer inundation periods enhance intra-specific competition and predation by fish and predatory insects (Batzer and Wissinger 1996).

Anthropogenic activities commonly alter wetland hydrology by either increasing or decreasing hydroperiod. Artificial impoundment prevents wetlands from drying out and shifts ephemeral wetlands towards pond ecosystems (Collinson et al. 1995), while groundwater withdrawal lowers regional water tables and results in decreased hydroperiods, thus shifting wetlands to more terrestrial systems, shorter hydroperiods and elimination of sensitive aquatic taxa (Watson et al. 1990).

In central Florida, groundwater extraction is a common practice to meet both municipal and agricultural needs. Pumping stations are clustered with municipal wellfields and lead to lowered local water tables and associated hydrological cones of depression (Nyman 1965) that can lead to shortened hydroperiod of aquatic ecosystems, soil subsidence (Watson et al. 1990), and a shift from aquatic to terrestrial plant communities (Haag et al. 2005).

Urban development, a second environmental stressor, often reduces landscape heterogeneity to form uniform urban landscapes (Reiss et al. 2007) with a high proportion of impervious surface areas that increase overland flow and discharge into water bodies (Ehrenfeld et al. 2003). Urbanization leads to great water level fluctuation in wetlands associated with the increased overland runoff. Hydroperiods and water levels often vary profoundly either

increasing or decreasing from natural conditions and urbanization can decrease wetland insect biological diversity by as much as 33% (Johnson et al. 2013).

Cypress domes are the most common ephemeral forested wetlands in central Florida and characterized by the tree species Taxodium distichum, and an annual hydroperiod typically longer than 6 months (Ewel and Odum 1984). They are the dominant forested wetlands (65%) in the Tampa Bay region of Florida and are preserved at a much higher rate than upland forest as a result of the Clean Water Act of 1972 (Grunwald 2006). With urbanization, these wetlands become increasingly isolated, and their physical and biological characteristics are altered by adjacent urban expansion. Given their high preservation rate and overall abundance, cypress domes are ideal for studying the impact of progressive urbanization on wetlands.

The temporal distribution of insect emergence in subtropical Florida is poorly known, but it is hypothesized that insect emergence will directly correlate with seasonal rainfall patterns rather than temperature or photoperiod, which are the dominant factors influencing emergence in most temperate North America wetlands (Ward 1982). The goals of the current study were to describe factors influencing seasonal emergence patterns of aquatic insect in wetlands of subtropical Florida. Emergence cycles were related to local rainfall patterns and varying hydroperiod to assess seasonality and insect community structure. Additionally, it was hypothesized that urbanization would decrease wetland insect emergence rates. Therefore, emergent insect communities were surveyed with a focus on how abundance and community structure related to hydrology and landscape structure.

Methods

Site Selection

Twenty five cypress dome wetlands were surveyed in northern Hillsborough County,

Florida within and adjacent to the Tampa metropolitan area. Site selection was restricted to wetlands between 0.5 and 5 hectares in area that were classified as cypress wetlands according to the Florida Land Use Cover Classification System (FLUCCS) and had no direct connection to river systems. Fifteen wetlands were selected in three municipal wellfields (J.B. Starkey (STK),

Cypress Creek (CYC), Morris Bridge Road (MBR)) that border the northern Tampa metropolitan area and are managed by the Southwest Florida Water Management District (SWFWMD) and

Tampa Bay Water (Figure 2.1). Wellfield sites were distributed across a hydrological gradient with mean wetland hydroperiod from 4 to 12 months annually. Wetland disturbance was estimated using WAP method (Wetland Assessment Procedures) (SWFWMD 2010) to grade wetlands based on disturbance indicators including vegetation, soil and hydrology. A hydrological gradient for wetland sites was based on annual mean water level deviation from normal pool elevation based on hydrological indicators including lichen lines and the buttress point of inflection for cypress (Carr et al. 2006). During the wet season most water levels approximate the normal pool value and decrease during the dry season.

Ten urban wetlands were selected, each having over 50% of the land area within 500 meters classified as urban, road, or industrial. Sites were divided into two subgroups relative to the time since initial urban development of the area: Urban Old (5 wetlands) with development prior to 1990 and Urban New (5 wetlands) with development post 1990.

Hydrology

Historic water level data for wellfield sites were obtained from SWFWMD staff gauge and ground water well records, while current water levels were measured at staff gauges for all wetlands. Wellfield staff gauges were installed by SWFWMD, while temporary staff gauges were installed in urban wetlands at the deepest point. Three additional water levels were recorded for 3 fixed sample locations within each wetland where emergence traps were deployed. Seasonal rainfall data were obtained from SWFWMD records at the nearest weather station (SWFWMD 2014).

Land Use

Landscape features (wetland forest, upland forest, scrub, urban/roads, open water) were classified using the Florida Land Use Cover Classification System layer provided by the Florida

Geological Database (FGDL 2008) in ArcGIS. Land use was calculated within 200, 500, and

1000 meters of each wetland; however, there were few differences among distance categories, so land use is displayed only for the 500 m diameter scale.

Insect Sampling

Insect surveys were conducted monthly from February 2012 to January 2014 to assess seasonality, community composition, and emergence timing. Insect identification was conducted to the Family level for all insects, but to genus for the Families Chironomidae and Culicidae

(Merritt and Cummings 1996). Three insect survey methods were used: emergence traps, malaise sampling and dip netting of aquatic insects. Emergent insect surveys were conducted throughout the study period, while malaise trap surveys were added during the second year of the study

(February 2013 through January 2014), and aquatic insect surveys were only conducted during periods of inundation following the first rainy season.

Insect emergence sampling was via floating pyramidal insect emergence traps with a water surface area of 0.25 m2 and a one way collection device with removable 250 mL sample bottle located at the top. Three traps were deployed at fixed locations at each wetland and included a shallow, intermediate and deep site. Traps were deployed for 24 hours, collected and brought back to the lab, where insects were identified after being euthanized by freezing for 24 hours. Total emergence rates were averaged among the three samples and calculated as insect emergence per square meter per day to standardize values and account for trap failures resulting from disturbance by white ibis, cats and raccoons.

Adult insects were surveyed using malaise traps to estimate the relative community composition of aerial insects including Diptera (Johnson 2000), which can account for 70% of all insects emerging from wetland forested systems in Florida (Leslie et al. 1997). A single, two meter high Malaise trap was deployed at ground level as suggested by Johnson and Sherry

(2001) monthly for a 24 hour period. The same preservation and identification method from the emergence surveys were used for Malaise samples.

Aquatic insect communities were sampled by dipnets only during periods of inundation beginning in July of each year. Samples consisted of 5 sweeps per wetland combined into a single sample. Each sweep measured 0.5 m in distance using a 0.25 m wide D frame dipnet.

Samples were preserved using 70% ethanol then returned to the lab for analysis. Specimens were sorted and identified to family under a dissecting microscope for all aquatic insects surveyed.

Data Analysis

Microsoft Excel and the software package R were used for statistical analysis. The influence of rainfall on water level was calculated using the Pearson’s product-moment correlation and a one month time lag. Relationships between temperature and rainfall on insect emergence were compared using a time series analysis and a Linear Regression Model. To determine changes in community structure, richness and the Shannon’s Diversity Index were calculated at both the Order and Family levels for urban and rural insect communities.

Stepwise General Linear Regression Models with AIC model selection criteria were used to determine which model best explained the effects of hydrology on emergent insect communities.

A generalized linear model was used to determine how urban insect communities responded to urban environmental factors.

Results

Summary Data

During the 24 month study (February 2012 through January 2014), 4226 emergent insects were collected representing 87 taxa and 10 insect orders. Dipterans accounted for 87% of all observations (n = 3674), followed by Hemiptera (n=114), Ephemeroptera (n=45),

Coleoptera (n=34), and Odonata (15). Arachnids and Orthopterans were observed in emergence traps but eliminated from further consideration because they are not considered emergent.

The order Diptera included 45 families and two suborders: Nematocera (12 families, 81% of dipterans) and Brachycera (33 families and 19% of dipterans). As noted elsewhere in the southeastern US (Leeper et al. 1998), Chironomidae was the most abundant family, accounting for 59% of total observations and 15 genera, the most common being Chironomus, Polypedilum,

and Tanytarsus. Other Diptera families of note included Dilochopodidae, Culicidae,

Ceratopogonidae, Simulidae, and Cecidomyiidae (Table 2.1).

Temporal Distribution

Central Florida has pronounced wet (June-October, mean monthly rainfall 17.28 cm month¯¹) and dry (November-May, mean monthly rainfall 6.9 cm month¯¹) seasons. Although cypress domes of the region typically dry out between November and March, four domes of this study did not dry out during the second year of study, and one (CYC 191) remained inundated throughout the entire two year study. Emergences were 15% higher during the wetter first

(February 2012 – January 2013) than the second (February 2013-January 2014) year. Wetland

191, which never dried, had a lower mean emergent insect abundance (3.99±1.3 insects’ m¯²day¯¹) compared to the overall wetland average (18.66±5.6 insects’ m¯²day¯¹), consistent with predictions that permanently inundated communities are structurally different than similar ephemeral wetland communities (Batzer and Wissinger 1996, Smith et al. 2009). Wetland 9014 suffered over 10 trap failures during the study as a result of wildlife tampering by roosting white ibis (Eudocimus albus).

Wetland water levels significantly correlated with monthly rainfall patterns at a one month time lag (Pearson’s r = 0.776, p = 0.003) (Figure 2.2). Wetlands re-flooded at the beginning of the wet season beginning in June, and then water levels progressively increased through August after which they steadily decreased until they either dried out or the next rainy season began. Seasonal insect emergence was compared with both water level and temperature using Pearson’s product-moment correlation and demonstrated that insect emergence was more strongly correlated with water level (r = 0.830, p = 0.001) than with temperature (daily high

temp., r = 0.280, p = 0.281). Emergence was highest during the wet season between July and

October (18.6±5.8 insects m¯²day¯¹), with a peak in July (29.4 ±6.52 insects’ m¯²day¯¹) and lowest during the dry season from January to June (6.1±4.1 insects m¯²day¯¹), with the lowest numbers coming in May at the end of the dry season (1.5 ±3.6 insects’ m¯²day¯¹) (Figure 2.3a).

Inundation began for most wetlands in June of both years, with insect emergence peaking in July (Figure 2.4). Thereafter, emergence declined steadily (R²=0.67, p=0.003, n=6) until wetland desiccation. The dipteran families Chironomidae (50%), Simulidae (29%), and

Culicidae (8%) were responsible for the July peak, accounting for 95% of emergence. Following the July peak, community succession was observed with a decline in Chironomidae emergence and an increase in aquatic insects with longer aquatic phases including members of Zygoptera,

Anisoptera, and Ephemeroptera, and emergence rates began to decline especially for many dipteran families. After flooding, predatory groups steadily increased in aquatic surveys, especially Anisoptera, Coleoptera, Ephemeroptera, Hemiptera, Megaloptera, and Zygoptera

(Figure 2.5), which showed a positive trend with inundation (R²=0.934 p=0.006, n=6).

Wellfield Insect Emergence

Hydroperiod varied among well-field groups, with CYC having longer, but not significantly different, inundation periods (9.7±1.56 months/year) than either MBR (7.5±1.96 months year¯¹), or STK (7.9±2.77 months year¯¹). Insect emergence positively correlated with hydroperiod for both abundance (r=0.463, p=0.048, n=14), and diversity (r=0.613, p=0.010, n=14). Insects, however, showed no significant emergence trend with water depth from 0.5 cm to 1 m, which accounted for 95% of observations (r=0.15, p=0.23, n=14). Annual emergence rates were significantly lower during the second year of study, likely due to the lack of a

significant dry season prior to the second wet season. Four wetlands were dry prior to the first wet season but did not dry down completely preceding the second (CYC 191, CYC 196, CYC

214, CYC 215, and MBR 264), and had significantly higher emergence rates during the first year

(4530±632 insects m¯² yr¯¹) than the second (2803±300 insects m¯² yr¯¹).

Urbanization

10 Urban wetlands were compared with 6 rural wetlands two from each wellfield (STK

435, STK 487, MBR 278, MBR 260, CYC 215, and CYC 196) displaying little environmental stress. Both mean annual hydroperiod (8.5 ±2.5 months urban vs 8.4 ±2.3 months rural) and mean water depth (31 ±11 cm urban vs 35±11 cm rural) were not significantly different between urban and rural wetlands. Based on detailed monthly monitoring in a subset of these wetlands in

2008, (Goddard 2010) dissolved oxygen was not significantly different between urban (1.7±0.34 mg l¯¹) and rural (MBR 2.2±0.5 mg l¯¹) wetlands, while pH significantly higher in urban wetlands (4.75 ±0.97 rural vs 6.53 ±0.4urban). Two wellfield wetlands where excluded from water chemistry and hydrological analysis in CYC (wetlands 191 and 214) because they are augmented with groundwater pumping that has changed their annual hydroperiod and water chemistry.

Landscapes were characterized within 200, 500, and 1000 meters of wetlands, but results are only presented for 500 meter range because varying scale results were not significantly different. Overall, the landscape surrounding urban cypress domes was 66% urban; with forested wetlands accounting for 12% forested upland 8%, and open water 10%. Land use adjacent to rural cypress domes had only 1% urban area, while forested wetland composed 33%, upland forest 38% and open water 5%. The Inverse Simpsons index of Dominance was used to

compare evenness and landscape heterogeneity between groups and indicated that rural sites had higher evenness (D = 3.25) than urban ones (D = 2.13).

Aquatic insect surveys indicated that rural wetlands had significantly higher aquatic insect richness at the order level (Rural n = 19.6 ±2.1, Urban n = 13.0 ±2.8) and diversity (Rural

H’ = 1.92±0.09, Urban H’ = 1.16 ±0.01) than urban sites, and the three most common aquatic insect orders observed in dipnet samples (Hemiptera, Coleoptera, and Diptera) had higher richness at the family level at rural than urban sites (Hemiptera R =10, U = 4), Coleoptera R = 9,

U = 3 and Diptera R =7, U = 2). Relative abundance did not differ significantly between urban

(111 ±53 sample¯¹) and rural wetlands (149 ±39 sample¯¹).

Emergent insect rates significantly corresponded with hydroperiod in urban wetlands

(r=0.669, p=0.03, n=8), the same as they did in rural wetlands, but insect diversity showed no relationship at all (r=-0.12, p=0.74, n=8). Urban wetlands actually had slightly higher emergence insect rates though not significantly (Urban =10.68±3.82 insects m¯² day¯¹, Rural = 8.59 ± 3.14 insects m¯²day¯¹). While richness did show a significant difference at the order level between urban and rural wetlands no difference was observed at the family level (Urban N = 37.5 ±0.7,

Rural N = 37.33 ±5.0). Rural sites had higher diversity at the order level, though no significant was observed at the family level (Figure 2.6). To determine community similarity among urban and rural sites, the Jaccard’s index was used and indicated that urban sites had the highest within group similarity at (J=0.63), indicating that rural insect communities showed more variation at the site level (J=0.48), indicating that urban and rural sites are very different and urbanization leads to decreased in community variation among wetlands.

The change in diversity among taxonomic levels can be attributed to the dominance of

Order Diptera among urban sites. Urban wetlands were proportionately higher in Dipteran

families and abundance that lead to their increased dominance. The Order Diptera includes, the most prominent groups of emergent insects, included the family Chironomidae that accounted for 59% of total emergence. High richness and diversity in this family is typically associated with higher water quality but here both abundance and species richness for Chironomidae were higher in urban sites, though water chemistry data (pH and conductivity) indicated evidence of pollution with pH increasing from 4.5±0.5 7.0±0.8 and conductivity increasing from

0.064±0.003 µS/cm to 0.183±0.015 µS/cm. Similar richness for Chironomidae at urban sites species = 6.2±2.3, compared to rural sites with species =6.0±1.2 Chironomidae, and urban sites even had 4 unique genera of Chironomids (Zaverelia, Potthastia, Einfeldia, and Tanypus) compared with only two for all rural sites (Ablesmyia, and Parachironomus). Chironomus was the most common genus and accounted for 34% of observations followed by Polypedilum at

23% and Tanytarsus at 8%. Chironomus emergence was highest in July, September, and

October (Figure 2.7a) and was lowest between February and April. Polypedilum displayed emergence patterns with peaks at 3 to 4 months intervals (March, July, and October) (Figure

2.7b). Pseudochironomus and Tanytarsus had winter emergences with the former peaking in

January (30% species annual emergence, Figure 2.7c), and the latter peaked in November (28% species annual emergence, Figure 2.7d). All other Chironomidae were combined and paralleled that of Chironomus Chironomidae peaking in September and October (Figure 2.7e). The mosquitoes (Culicidae) displayed a single peak during July (43% their annual emergence) and where primarily found in CYC and STK rural wetlands (62% of observations).

While the emergent insect community did not significantly vary between urban and rural sites, surveys of aerial adult insects showed that urban sites had significantly lower adult insect abundance (urban n = 4.17±0.05 day¯¹) than did rural ones (rural n = 5.94±0.78 day¯¹) and

lower richness though not significant (urban n = 29±0 site¯¹, rural n = 32± 4 site¯¹). Insect captures were lowest in May (n =1.72 day¯¹) and June (2.02 insects day¯¹) at the end of the dry season (Figure 2.3b). Following inundation, adult captures showed a small spike in July (n =

5.28 day¯¹) then increased progressively until February (likely due to continual replenishment of the community by emerging aquatic insects) except for a dip in January due to the coldest annual daytime temperatures. While insect emergence rates peaked in July then trended downwards, the wetland adult insect community, which was composed of by over 90% aquatic insects, showed a positive trend increasing until around February when the majority of wetlands dried out, then after most wetlands had dried completely there was a noticeable decline in the adult insect population until July when wetlands re-flooded.

To determine what factors had the greatest influence on urban emergent insect communities a Stepwise Linear Regression Model with AIC selection criteria to find the model of best fit. The aim of first analysis was to determine factors influence emergent insect diversity calculated using the Shannon’s diversity index. Independent variables included hydroperiod, water level, pH, urban land area, forest land area, and open water land area. The model that best explained the variance included two variables, forest area and hydroperiod (F= 5.33, R² = 0.35, p=0.013). The insect community was then divided into two groups; the Order Diptera, and all remaining non-Dipteran emergent insects. The final Diptera model included hydroperiod and open water area (F = 4.76, R² = 0.32, p=0.02), while the non-dipteran model only incorporated the urban land parameter, which was negatively related to abundance (F = 7.58, R² = 0.27, t=-

2.75, p=0.01).

Discussion

In most of North America insect emergence is driven by seasonal environmental factors, the most important being temperature (Ward and Stafford 1982). Changes to temperature can alter emergence patterns as documented for release of warm water from power plants (Vannote and Sweeney 1980) and climate change (Burgmer et al. 2007). In Central Florida insect emergence is strongly influenced by hydrology and rainfall patterns with emergence rates increasing from 1.5±3 insects’ m¯²day¯¹ at the end of the dry season in May to 29±6 insects’ m¯²day¯¹ in July with the onset of the rainy season. Emergence rapidly increased following the onset of the rainy season in then steadily declined as standing water persisted, previously described by Batzer and Wissinger (1996). This trend is attributed to an initial pulse in emergence following re-flooding to insects either able to withstand dry period’s in situ or fast colonizers with a short larval stage. Early pioneers decrease over time as additional taxa that are better competitors are able to colonize the wetland leading to enhanced competition and predation (Stagliano et al. 1996, Wilcox 2001).

Those aquatic taxa that can withstand dry periods in situ do so by either vertically migrating in wetland soils following the capillary fringe of the water table (Leslie and Crisman

1997), or by entering diapause and estivating in the soil as desiccation resistant life stages

(Wiggins et al. 1982, Neckles et al. 1990). The earliest colonizers after flooding wetlands face little competition (Brock et al. 2003), and in the current study, consisted primarily of the dipterans families Chironomidae and Culicidae that accounted for 59% of emergence during the first two months after flooding. These two families include many pioneer species that can complete their larval development within a few weeks of inundation, thus avoiding expected of high competition and predation thereafter (Armitage et al. 1995, Williams 1996, Juliano et al.

2003). Colonization following re-flooding can be rapid (Wissinger 1997), but it is highly variable depending on landscape and dispersal ranges of local taxa (Batzer and Resh 1992). This can lead to high seasonal variability among transitional communities where both competition and predation within insect communities increase following initial inundation, offsetting advantages of early colonizers (Bunn and Arthington 2002).

In the subtropical Tampa Bay region, wetland environmental impacts associated with anthropogenic activity can be divided broadly into two categories: hydrologic alteration associated with groundwater pumping of local water tables to meet regional municipal and agricultural water needs, and urbanization and the transformation of large tracts of rural land.

Groundwater extraction to meet the domestic needs of the metropolitan areas of Tampa Bay has imposed a major hydrological stress on cypress domes of the area since the 1970’s (Zektser et al.

2005, Glennon 2012). Regional geology of the northern Tampa Bay area is dominated by karstic limestone and sand, often with a semi confining clay layer (WRAP 1996), resulting in high connectivity between wetlands and the underlying water table and aquifers (Watson et al. 1990).

Over extraction of groundwater for municipal and agricultural purposes (Scholtz and Stiftel

2005) has resulted in a lowering of the local water table and a pronounced cone of depression around well heads (Bacchus 2000) that have both temporary and long term impacts on adjacent wetlands depending on the timing, duration and total volume pumped (Haag et al. 2004).

Reduction in annual hydroperiod can directly affect total annual insect emergence with lowest abundances found in wetlands with the shortest hydroperiods. Hydroperiod was not only important for early emergent insect groups including Chironomus and Culicidae but also seasonal insects occurring later in the year and winter species of Tanytarsus and

Pseudochironomus that peaked during November and December, respectively, when wetlands

impacted by pumping are often dry. At the other end of the hydroperiod continuum, one of study wetlands was permanently impounded as a result of augmentation with groundwater pumping and displayed both the lowest insect abundance and a shift from a wetland to lotic insect community (Batzer and Wissinger 1996).

The second factor affecting wetland insect communities during this study was urbanization of the pre-existing landscape of forested wetlands, pine flatwoods, and scrub. While upland forest and scrub lands accounted for >50% of rural area, it declined to < 5% in urban areas. Urbanization was also accompanied by a reduction in the area of forested wetlands, and an increase in lakes and retention ponds and marshes, common mitigation options associated with development plans. The decreases in natural lands could be the greatest factor limiting colonization of aquatic insect species. Insect diversity was significantly lower for every insect group but the order Diptera in urban wetlands. Urban non-dipterans insects displayed a 45% lower abundance and 33% richness than in rural wetlands. The fact that emergence rates for

Dipterans, especially Chironomidae, were highest in urban sites may reflect reduced predation associated with lower populations of Hemiptera, Odonata and Coleoptera. While emergence rates did not differ significantly among urban wetlands the standing crop of adult insects was significantly lower than in rural sites. The disagreement between emerging insects and adult abundance data may be the result of a combination of factors. First, the urban landscape is more difficult to traverse because of lower habitat quality as forests are replaced by open urban landscapes that provide less refuge from aerial insectivores like swifts, swallows and bats and leads to a decline in adult insects (Fahrig 2003, Faethet et al. 2005).

Within the wetlands, the abundance of predatory insect groups is reduced in response to altered hydroperiod. Finally, the impact of urban mosquito control activities may be significant.

Hillsborough County Mosquito Control uses a combination of adult and larval targeting insecticides for control of residential mosquito and midge populations (Hillsborough Mosquito

Control 2015). Insecticides are routinely applied throughout all urban areas but not in rural wellfield areas. Target insects of the mosquito control measures are Culicidae and Chironomidae

(Howarth 1991, and Milam et al. 2000); however, mosquito and midge targeting insecticides are not a ‘clean’ control method and have a number of both lethal (Ali and Mulla 1978, Niemi et al.

1999) and non-lethal (Desneux et al. 2007) effects on a wide range of other invertebrates.

Human activity has substantial impacts on wetland insect communities through both hydrological and physical alterations. Groundwater pumping and urbanization alter ecological function of cypress dome wetlands reducing species richness diversity and annual emergence rates of aquatic insect communities. Current climate change models for peninsular Florida indicate that in the next 100 years much of the central region of Florida will experience a decline in annual rainfall (Coehen 2010). If models such as this one are correct then the changing climate will likely lead more cypress domes in the region to experience shorter hydroperiods and may start to resemble conditions observed in impacted wetlands of the current study of wellfield wetlands. Many winter emergent insects, such as Tanytarsus and Pseudochironomus, rely on these temporary water bodies and may suffer significant local declines if predictions hold.

Declines in winter insect communities would thus likely have a negative influence on forest dwelling migratory birds that rely on these insects as a main food source and utilize the area as their primary wintering grounds, including the yellow rumped warbler.

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vegetation in a created wetland and implications for sampling. Wetlands, 15, 285-289.

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Table 2.1. Emergent insect counts both for important Dipteran Families and Genera and non- Dipterans Orders. Table includes total insect counts over two year sampling period from February 2012 through January 2014. Diptera families with single observations were excluded*.

Site Group Order Family CYC MBR STK UNEW UOLD Diptera Cecidomyiidae 43 52 28 35 19 Diptera Ceratopogonidae 18 17 46 20 8 Diptera Chaoboridae 72 23 32 17 22 Diptera Chironomidae Ablabesmyia 1 3 5 Diptera Chironomidae Chironomus 65 94 93 174 199 Diptera Chironomidae Cryptochironomus 13 18 13 11 3 Diptera Chironomidae Einfeldia 7 Diptera Chironomidae Glyptotendipes 4 16 1 Diptera Chironomidae Goeldichironomus 4 19 12 17 12 Diptera Chironomidae Kiefferulus 4 8 1 4 1 Diptera Chironomidae Parachironomus 5 Diptera Chironomidae Polypedilum 115 57 24 89 126 Diptera Chironomidae Potthastia 3 Diptera Chironomidae Prodiamesa 5 1 Diptera Chironomidae Pseudochironomus 77 32 60 86 15 Diptera Chironomidae Tanypus 1 Diptera Chironomidae Tanytarsus 25 55 25 94 97 Diptera Chironomidae Zavrelia 3 Diptera Chironomidae Total 548 635 421 775 599 Diptera Culicidae Aedes 8 7 3 5 Diptera Culicidae Anopheles 1 13 9 9 Diptera Culicidae Coquillettidia 1 1 Diptera Culicidae Culex 23 15 1 1 1 Diptera Culicidae Mansonia 1 Diptera Culicidae Ochlerotatus 1 Diptera Culicidae Psorophora 1 1 3 4 1 Diptera Culicidae Uranotaenia 9 7 8 7 1 Culicidae Diptera Total 45 45 14 25 20 Diptera Dolichopodidae 80 101 63 49 75 Diptera Empididae 4 3 1 3 8 Diptera Ephydridae 4 4 7 11 23 Diptera Muscidae 5 3 9 19 40 Diptera Sarcophagidae 31 71 89 43 43 Diptera Sciaridae 9 16 1 69 5 Diptera Simulidae 9 5 207 5 13

Table 2.1. (continued)

Site Group Order Family CYC MBR STK UNEW UOLD Diptera Tipulidae 13 8 5 19 67 Diptera Total* 933 1043 941 1129 1014 Coleoptera 16 19 12 57 8 Ephemeroptera 25 8 17 8 4 Hemiptera 54 29 20 35 34 Hymenoptera 7 25 17 11 20 Lepidoptera 11 13 15 15 15 Megaloptera 1 1 3 Neuroptera 4 10 4 4 13 Anisoptera 1 1 1 Zygoptera 3 6 1 3 Orthoptera 11 18 20 4 3 Trichoptera 3

Table 2.2. Statistical model number 1 shows Shannon’s Diversity at the lowest taxonomic level; model 2shows abundance of all members of order Diptera; and model 3 shows Non-Diptera abundance. * denotes statistical significance of > 0.05, ** denotes statistical significance > 0.01.

Model Parameter Estimate SE t value p

Model 1: Insect Diversity (Shannon's), Forest Area, Hydroperiod (Intercept) 1.613 0.2912 5.8 2.02E-05 ** Forest 5.898E-07 2.313E-07 2.55 0.019 * Hydroperiod 0.03574 0.01686 2.12 0.046 * F=5.335, Res. SE = 0.3084, Multiple R² = 0.35, DF = 2 and 20, p-value = 0.013

Model 2: Diptera abundance, Hydroperiod, Open water land area (Intercept) 47.75 44.24 1.079 0.2933 Hydroperiod 5.619 2.6 2.161 0.043 * Open Water 0.000567 0.0002504 2.264 0.0348 * F=4.76, Res. SE = 47.57, Multiple R² = 0.32, DF = 2 and 20, p-value = 0.02

Model 3: Non-Diptera abundance, Urban Land Area (Intercept) 4.943 0.3705 13.341 1.01E-11 ** Urban Land -0.000002089 7.587E-07 -2.753 0.0119 * F=7.57, Res. SE = 1.39, Multiple R² = 0.26, DF = 2 and 20, p-value = 0.0119

Figure 2.1. Map of cypress dome wetland study sites in the Northern Tampa Bay Region of Florida.

18 70 Rainfall

16 60

14 Water Level 50 12 10 40 8 30 6

20 Water Level (cm)

Rainfall Rainfall (cm¯¹ month¯¹ 4 2 10 0 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Figure 2.2. Mean annual rainfall for Hillsborough County FL collected by SWFWMD mean wetland depth for sampled wetlands monthly from February 2012 through January 2014 from this study.

45 80 14 80 Emergence Adult Insects

40 70 12 70

35 60 60

10 30 50 50 25 8 40 40 20 6 30 30

15 Insects day¯¹

Water level (cm) Water Level (cm)

Insects m¯²day¯¹ 4 20 10 20 2 5 Insects 10 Insects 10 Water Level Water Level

0 0 0 0

Jul

Jan

Jun

Oct

Apr

Feb Sep

Jan

Dec

Jun

Aug

Oct

Nov

Apr

Feb Sep

Mar

Dec

Aug

May

Nov Mar May

Figure 2.3. Insect communities compared monthly with water level (2a) Insect emergence rates per square meter per day (2b) and Adult insect communities surveyed monthly using malaise traps) with water level.

9 8 n =14 n=8 7 n=14 n=14 6 n=8 n=10 5 n=10 n=6 4

3 Insectsday¯¹ m¯² 2 n = 14 1 0 0 2 4 6 8 Months Inundated

Figure 2.4. Insect emergence plotted against the number of month wetland has been inundated; numbers indicate the total wetlands calculated during each month.

1.8 n=8 1.6

1.4 n=8 1.2 1 n=10 0.8 n=10 0.6

Predatorsm²day¯¹ 0.4 n=14 n=14 n=14 0.2 n=14 0 0 2 4 6 8 Months Inundated

Figure 2.5. Average predatory insects abundance per square meter per site including the groups Coleoptera, Hemiptera, Odonata, Ephemeroptera, and Megaloptera per m² per day.

0.65 3

0.6 2.8

0.55 2.6

0.5 2.4

0.45 2.2

Order Level OrderLevel Diversity Family Family Level Diversity 0.4 2 CPC MBR STK U OLD U NEW CPC MBR STK U OLD U NEW

Figure 2.6. Shannon diversity index for insect Order and Family for emergence traps by sample group over the 24 month study period.

Chironomus 7

5 4 3

2 Insects m¯²day¯¹ 1

Jul

Jan

Jun

Oct

Apr

Feb Sep

Dec

Aug

Nov Mar a. May Polypedilum Pseudochironomus

3.5 5

3 4 2.5 2 3 1.5 2

1 Insects m¯²day¯¹ Insects m¯²day¯¹ 1 0.5

0 0

Jul Jul

Jan Jan

Jun Jun

Oct Oct

Apr Apr

Feb Sep Feb Sep

Dec Dec

Aug Aug

Nov Nov

Mar Mar May b. May c. All Others Tanytarsus 10

5 8

4 6 3 4 2

1 Insects m¯²day¯¹ 2 Insects m¯²day¯¹

0 0

Jul

Jan

Jun

Oct

Apr

Oct

Feb Sep

Apr

Feb Sep

Dec

Aug

Nov

Mar

Mar May d. e. May

Figure 2.7. Monthly emergence rates for Chironomidae Genera; a. Chironomus, b. Polypedilum, c. Pseudochironomus, d. Tanytarsus, and e. remaining genera combined (Ablabesmyia, Cryptochironomus, Einfeldia, Glyptotendipes, Goeldichironomus, Kiefferulus, Parachironomus, Potthastia, Prodiamesa, and Tanypus).

CHAPTER THREE

RELATIONSHIPS AMONG WETLAND HYDROPERIOD, INSECT SEASONALITY,

AND NEOTROPICAL BIRD MIGRATIONS IN WEST CENTRAL FLORIDA

Abstract

As the human population increases, natural habitats that are suitable for sensitive urban avoiding taxa decrease. This has management implications for migratory birds because the reliability of seasonal food resources is vital during migration, when migrants are dependent on food resources at key times and locations including the spring breeding season, winter season, and during migration between the two regions. The majority of forest dwelling birds in the Eastern

United States are insectivorous, and wetland are areas with high insect productivity. In Central

Florida, cypress domes are some of the most common forested landscape features, and migratory birds favor these habitats during their migrations because of high insect productivity. However, municipal water suppliers obtain the majority of the local water supply from groundwater extraction which has negative environmental consequences by decreasing local water tables and shortening hydroperiods of surrounding wetlands. This study surveyed forested wetlands in 3 municipal wellfields that had varying hydroperiods associated with hydrological influences from groundwater pumping. Results indicated that aquatic insect populations fluctuated seasonally and directly responded to local rainfall and inundation. Annual insect production was higher at

sites with longer annual hydroperiods (r = 0.463, p = 0.048). Winter migratory birds (November

- February) showed a positive response to adult insect abundance (r = 0.578, p=0.049), while

Neotropical migrants, with short residence times, showed little response and likely select sites based of environmental cues. Total insectivorous bird communities positively correlated with insect emergence and suggested conservation practices that favor lower withdrawal rates would likely have a positive influence on both insect and insectivorous bird communities of the region.

Introduction

Forested wetlands are important habitats for forest dwelling migratory birds, the majority of which are insectivorous and migrate along the Atlantic Flyway to and from breeding grounds in eastern North America (Moore et al. 1995). Wetlands are common in the southeastern united states and especially in Florida where they account for 27% of total land area (Dahl 2005), 55% of which are forested wetlands (Haag et al. 2010). But in the United States, wetlands have declined by approximately 50% since colonial times, 46% for Florida (Dahl 1990), with serious consequences for biota dependent on such systems for all or part of their life cycle.

Cypress domes are the most common forested wetlands in central Florida (Mathiyalagan et al. 2005) and are dominated by Taxodium distichum, a species that requires both an extended hydroperiod of 6 to 10 months (Ewel and Odum 1984) accompanied by dry periods required for seed germination (Young et al. 1995). Cypress domes are often poorly connected with other surface-water systems under normal flow conditions, a characteristic that is beneficial to aquatic insect communities because it impedes colonization by fish (Vernon 1947).

The population of Florida has seen a dramatic increase recently, more than doubling between 1980 and 2015 from 9 million to over 19 million (Bogue et al. 2010, US Census Bureau

2015). Recognizing the need to protect natural lands (Simberloff 1993), provisions of the Clean

Water Act has been enabled protection of cypress domes along with other wetlands of high biological value (Alder et al. 1993).

Groundwater is the main source of water for municipal and agricultural purposes in west central Florida (SWFWMD 1996). Groundwater pumping is often clustered in wellfields situated on large rural tracts. While these large tracts of land are extremely valuable for wildlife, many freshwater ecosystems have been drained in association with lowering of the water table via pumping (Rochow 1994, Sophocleous 2002). The most pronounced drainage is often directly adjacent to surrounding wellheads, or cone of depression (Winter 1988), and decreases with distance from wells (Ricter et al. 1996). Depressed water tables shorten wetland hydroperiods, altering both the structure and ecological function of wetland biota (Glennon

2012). In the region’s most severe cases, wetland plant communities have shifted from cypress domes and wetland mixed hardwood forests to marsh wetlands or uplands (Carr et al. 1998).

Altered hydrology results in profound changes to wetland foodwebs (Boulton 2003, and

Schindler and Donahue 2006) including aquatic insect communities reliant on standing water to complete their life cycles. Wetlands with extremely short hydroperiods are dominated by

Chironomidae and Culicidae, whose aquatic development phase can be as short as two weeks, while insects such as Zygoptera and Anisoptera may be excluded by their need for longer hydroperiods (Merritt and Cummings 1996). Both community richness and diversity increase with hydroperiod leading to elevated competition and predation (Brooks 2000, and Wilcox

2001). Permanent inundation, however, leads to a shift from wetland to pond, with associated shifts in aquatic invertebrate communities, decreased insect emergence rates (Batzer and

Wissinger 1996) and fish colonization and predation (DeAngelis et al. 2005). Dry periods are the

key to resetting wetland communities and maintain both biological integrity and community structure (Dorn 2008). So hydrological drawdown reduces wetland hydroperiods (Bunn and

Arthington 2002, Dorn 2008) shortening hydroperiods during fall and winter and excluding winter emerging insects which have potential negative impacts on insectivorous birds that depend on them (Baber et al. 2004, Johnson and Sherry 2001).

Florida insectivorous bird communities include residential non-migratory birds as well as migratory birds that utilize the region during some period of their annual migrations.

Insectivorous birds fall into three major guilds based on their life history (Degraaf and Rappole

1995): resident non-migratory birds use the area year round, Neotropical migrants visit for a short period during their migrations between Nearctic breeding grounds of North America to wintering grounds in Central and South America, and winter migrants (short-distance migrants) breed in the same regions as Neotropical migrants but migrate much shorter distances to winter in central Florida.

Changes in local insect populations are likely to affect overall quality of individual wetlands and their relative ability to support insectivorous bird populations (Johnson and Sherry

2001). Seasonal and inter-annual variations in insect populations and community composition

(Cowell and Carew 1976) are strongly influenced by local environmental conditions, spatial distribution of similar habitats, and the predictability of seasonal hydrological patterns such as hydroperiod and draw-down (Williams 1996). Unique to eastern North America, Central

Florida’s subtropical climate is driven more by seasonal rainfall (wet and dry seasons) than annual temperature fluctuations as elsewhere in eastern North America (Duever et al. 1994). The wet season runs from June through October and has an average monthly rainfall of 10.29 cm

month¯¹, and a dry season is from November through May with an average monthly rainfall of

5.25 cm month¯¹ (SWFWMD 2014).

While bird migrations have evolved to coincide with seasonal food resources such as insect emergences and fruit ripening at the migration endpoints (Alerstam et al. 2003), intermediate habitats en-route may possess seasonally unfavorable conditions that must traversed to reach their goals in a timely manner. This situation likely contributes to the extremely high proportion of annual mortality occurring during migratory events, which have been observed as high as 67 – 71% of annual mortality in black throated blue warblers (Sillett and Holmes 2002).

To reach their seasonal habitats, migrating birds must pass through unfamiliar territory.

If food limitation does exist, critical stopover points along the migratory route, including immediately preceding or following large geographic barriers including deserts or large bodies of water, food scarcity can become a limiting factor to an entire population (Newton 2004).

Synchronicity of the migratory bird arrival and insect emergence is well documented for both breeding (Webster et al. 2002) and wintering areas (Norris et al. 2004) and can strongly influence seasonal population trends, but there is little information on the importance of such synchronicity at critical points along the migratory route for migratory bird populations (Newton

2006).

Neotropical migrants pass through central Florida during their spring migration from

February through June, which coincides with the second half of the dry season and may affect emerging insect populations, which are important dietary components for forest dwelling migratory birds (Smith et al. 2010). When entering the area during the spring migration birds arrive by way of long open-water flights from Cuba and Central America. These open ocean flights leave birds with depleted energy reserves (Moore and Kerlinger 1987) at a time when

insect emergence rates and production are likely at their lowest since wetlands have been dry for extended periods. This leaves habitats susceptible to depletion of adult insect food resources

(Moore and Young 1991) and may have negative consequences for birds migrating later in the season. Because of large scale fragmentation of forest area in Central Florida from development and an unfavorable timing in seasonal food availability during the spring, there is the potential for this region to act as a limiting factor on some Neotropical species, and the selection of habitats with diminished food resources resulting from groundwater pumping may further threaten these communities. Alternatively, the fall migration, August through October, is at the end of the Florida wet season, and is likely to have much higher insect emergence rates than spring.

Winter migrants are a group commonly classified as short distance migrants, many of which winter in Central Florida. This migratory group is likely to be less affected by seasonal limitations in insect populations because they are present from November through February which comes directly following the rainy season when most wetlands in the area are still flooded and insect populations are abundant, though no comprehensive data are available for insect abundances in the area. However, as the dry season persists, insects abundances likely decline throughout the winter dry season as wetlands dry out, beginning with those that are hydrologically impacted by groundwater pumping. Sites that dry out earlier may become lower quality foraging areas later in the season and prove of little value to birds during the second half of their winter stay.

Groundwater pumping leads to shorter hydroperiods and wetlands with longer hydroperiods that suffer less hydrological impact are predicted to have higher insect emergence and adult insect populations. Resident and wintering birds that reside in the area for longer

periods are predicted to show a stronger response to local insect abundance than Neotropical migrants and are predicted to show the strongest relationships with relative insect abundances.

The goal of this project was to determine how wetland hydrological patterns affect insect abundance, then how insectivorous birds respond to seasonal and spatial variability in local insect populations.

Methods

Study Sites

Cypress dome wetlands were selected as the primary sampling unit for this study. A total of 15 wetlands were surveyed monthly from February 2012 to January 2014. Study sites were located in three wellfields in the Tampa Bay area managed by the Southwest Florida Water

Management District: J.B. Starkey, Cypress Creek, and Morris Bridge Road with 5 cypress domes selected within each.

Study wetlands were selected using the Florida Land Use Cover Classification System map imagery provided by the Florida Geological Data Base (FGDL 2008). Hydrological data for all cypress dome wetlands between 0.5 and 5 hectares that represented a hydrological gradient with mean wetland hydroperiods ranging from 4 to 12 months annually, and ranged from little disturbance to highly influenced wetlands with reduced hydroperiods and physical indication of hydrological disturbance including soil subsidence and mature tree mortality.

Historical water level data and wetland the wetland normal pool elevation for prospective wetlands were also used estimate potential hydrological disturbance. The annual mean water level for each wetland was calculated by averaging monthly water levels for each wetland, and then comparing mean water level with the historic normal pool elevation. Normal pool level is

determined by hydrological indicators including a cypress tree buttress point of inflection and lichen lines and was obtained from SWFWMD records for each prospective site (SWFWMD

2010, Carr et al. 2006). The distance between the normal pool level and the annual mean water level should differentiate wetlands drying quicker from those with longer inundation periods.

While water levels for all wetlands should approximate the normal pool value during the rainy season, during the dry period water levels will theoretically decrease faster in hydrologically altered sites with depressed local water tables, and differences in dry season groundwater levels should drive mean water levels further from the normal pool in impacted sites.

Bird Surveys

Birds were surveyed monthly for a two year period using fixed radius point counts within

3 hours of daylight, which is considered the period of greatest diurnal bird activity (Bibby 2000).

Point counts consisted of a 40 meter radius and were conducted for a period of 5 minutes. This method calculates bird density and the area is less than the smallest selected wetland’s areas.

Birds were counted only within the survey radius, and individuals flying over or beyond the wetlands were excluded. Relative abundance was calculated for each point count location on a monthly basis.

Bird communities were broken into insectivores and species with a significant insect dietary component and non-insect eating species. All analyses were restricted to insect consuming species, and birds were grouped into migratory guild: resident non-migratory birds, wintering or short-distance migrants, and Neotropical migratory birds. The latter were further separated into breeding Neotropical migrants with populations breeding in central Florida and en-route Neotropical migrant lacking significant Florida breeding populations.

Insect Surveys

Wetland insect surveys communities were surveyed using two methods, emergent insect traps and adult insect trapping using malaise block traps. Since insect community composition does not effectively describe food availability for insectivorous migratory songbirds (Cooper and

Whitmore 1990) due to foraging prey size restrictions, insects greater than 10 mm in length were excluded from statistical analysis because they are not actively consumed and thought to be too large for consumption by most neotropical migratory songbirds (Johnson and Sherry 2001).

Emergence traps were used to determine insect emergence timing and intensity. Three traps were deployed monthly in each wetland for a period of 24 hours to calculate emergence rate per square meter per day. Floating pyramidal emergence traps were used with an open bottom that had surface area of 0.25 m² and a removable collection device at the top. Members of the families Chironomidae and Culicidae were identified to genus, while all other insects were identified to the family.

Adult insects were surveyed using malaise traps that passively collect insects as a block trap and estimate relative abundance of adult aerial insect communities (Johnson 2000). Malaise traps were 1.5m x 2m and deployed for the second year of study from February 2013 through

January 2014 concurrent with emergence trap sampling (Johnson and Sherry 2001). Trapped insects were returned to the lab, sorted, and identified to family for all insects and then to genus for Chironomidae and Culicidae (Merritt and Cummings 2006).

Physical parameters collected included water level, temperature, rainfall and hydroperiod.

Water level data were collected monthly concurrent with biological samples and validated using

monthly water data collected by the SWFWMD. Annual hydroperiod was determined as the number of months in which standing water remained in wetlands. When no standing water remained below staff gauges, but soils were saturated and puddles were observed in wetlands the depth reading was corrected to 0.5 cm of depth to indicate that wetlands were not completely dried. Rainfall and temperature data were obtained from the nearest SWFWMD weather station to each wellfield area (SWFWMD 2014).

Analysis

Data were compiled in Microsoft Excel with statistical analysis ran using packages SPSS

(from IBM), the open access statistical package R, and PRIMER 6. Bird counts were compiled by site, and seasonal trends for migratory bird groups were determined using Pearson’s product moment correlations. Multiple regression models were used to characterize seasonality of migratory bird populations, and a structural equation model was used to determine the influence of hydrology and insects on total insectivorous birds. Sites were characterized and classified by annual hydroperiod into Low, Intermediate and High. Pearson’s correlations compared wetland groups with both insect communities and bird communities on both an annual and study wide basis.

Bird communities were separated by migratory guild and seasonal population trends were assessed for each bird group. Insect communities were compared with hydrological factors including hydroperiod and water depth. Data were compared both monthly for the entire study, then by year with the first year running from February 2012 – January 2013, and the second from

February 2013 – January 2014. Insect community responses to hydroperiod were compared

separately for the two years to determine if sustained dry-downs had any effect on wet season insect communities in cypress domes.

Insect bird interactions where compared using linear regression models to compare bird abundances with both insect emergence rates and adult insect communities. Data were transformed prior to analysis using logarithmic transformations of insect community and bird abundances, while species richness analysis used presence absence data. Individual migratory communities where restricted to only the seasonal periods in which they utilize the region.

Winter migrant analyses were restricted to November through February, and Neotropical birds where restricted to February through June then September.

Results

Birds

During the study, 4954 individuals were observed from 89 bird species. Insectivores and other species with a significant insect diet accounted for 63% of observations (3993 individuals and 64 species) and comprise the current study. Bird species were assigned to migratory guilds including resident non-migratory birds (17 insectivorous species, of 40 total species), winter migrants that utilize the area (13 insectivores, of 18 total species), and Neotropical migratory birds that were further divided into two groups: en-route Neotropical migrants (28 insectivores, of 31 total species), and breeding migrants that are typically classified as Neotropical migrants but include individuals breeding in central Florida (insectivores 5, of 5 total species).

Populations of insectivorous birds fluctuated seasonally with the highest numbers during winter and lowest in summer (Figure 3.1). The resident insectivorous bird community (47% of observations) showed no seasonal fluctuations confirming that species were properly classified

(Figure 3.2a). The greatest contributors of seasonal variation in insectivorous birds were wintering (short-distance) migrants, which were the dominant migratory group (58% of migrants) and utilized the region from November through February (Figure 3.2b). Winter migrants included 13 insectivorous species, of which 5 accounted for 89% of observations. In descending order of abundance they were: Yellow-rumped warbler (Setophaga coronata), Palm warbler (Setophaga palmarum), Grey catbird (Dumetella carolinensis), Pine warbler (Setophaga pinus), and Prairie warbler (Setophaga discolor).

The two subgroups of Neotropical migrants, en-route and breeding Neotropical migrants showed a nearly identical seasonal pattern (r = 0.907 p=0.0001), likely because breeding species do include individuals breeding in Florida although most breed much further north. The five breeding species included, in order of abundance: northern parula (Setophaga americana), white eyed vireo (Vireo griseus), yellow throated warbler (Setophaga dominica), black and white warbler (Mniotilta varia), and yellow throated vireo (Vireo flavifrons). Although the breeding migrants had the larger population, both Neotropical groups displayed similar seasonal trends

(Figure 3.2c and 3.2d) with much higher detection rates during spring than fall migrations.

During spring, migrants arrived in February with peak migration in April and May, while fall migrants began returning in August and peaked in September as noted in other migratory studies

(Richardson, 1990).

Insects and Hydrology

Water levels in cypress domes fluctuated seasonally in response to the subtropical climate of central Florida with its annual wet (June to October) and dry (November to May) seasons.

Wetland water levels were significantly correlated with the annual Florida rain cycle (r = 0.776,

p = 0.003) (Figure 3.3). Following the start of the rainy season in June, insect emergence rates rapidly increased as wetlands re-flooded and peaked in July, then steadily declined into the dry season with declining water levels (November – May). Emergence rates positively correlated with hydroperiod (r=0.463, p=0.048, n=14) and were highest at the beginning of the rainy season

(July = 31.8 m¯²day¯¹ ± 26.2) and lowest during the dry season (May = 1.48 m¯²day¯¹ ± 3.09).

Sites were grouped into three categories based on length of annual hydroperiod: High

(longest hydroperiod) of 8.5 - 11 months (sites CYC 196, CYC 215, MBR 264, and STK 435), intermediate hydroperiod of 6 - 8 months (CYC 199, MBR 260, MBR 273, MBR 278, and

STK487) and Low (shortest hydroperiod) of 4 - 5 months (MBR 293, STK 444, STK 485, and

STK 498) (Figure 3.4). Two wetlands (191 and 214) were excluded from the classification scheme because they had groundwater augmentation for mitigation purposes. Both hydrology and emergence displayed major inter-annual variation during the study. Year 1 of the study followed an extremely dry year when all 13 non-augmented wetlands were dry for more than 2 months prior to the 2012 rainy season; however, during Year 2, five wetlands were dry for 1 month or less. There was a 24% decline in insect emergence during Year 2 following a wet winter with little to no dry down, versus year 1 following a sustained wetland dry period of over

2 months (Figure 3.5), and it should be noted that mosquitofish (Gambusia holbrooki) were observed in all wetlands during the second year.

Insect emergence during Year 1 displayed a significant positive relationship with annual hydroperiod length (R² = 0.36, p = 0.023). However, following a wet dry season of Year 1-2 when many wetlands never dried completely no significant relationship was observed for emergence during Year 2 (R² = 0.034, p = 0.52) (Figure 3.6). This is in agreement with Batzer and Wissinger’s findings that wetland community succession leads to communities more

representative of lentic systems with sustained inundation. The wetlands with short hydroperiods where similar between years, but those with longer hydroperiods and that didn’t dry after the first wet season showed much lower annual production during the second year.

Wetlands with extremely short hydroperiods (4-6 months) had consistently lower annual insect production. They excluded two common genera winter emerging aquatic insects all together,

Tanytarsus and Pseudochironomus that were common to cypress wetlands and have peak emergence in November and January respectively. Other emergent insects that were significantly reduced with decreased hydroperiods included the members of Culicidae (Aedes,

Anopheles, Culex, and Uranotaenea), Chironomidae (Goeldichironomus and

Cryptochironomus), and Ephydridae.

Wetland insects surveyed including both emergence and aerial adults were dominated by the order Diptera and were similar to communities of other isolated wetlands types in the southeastern United States (Leeper and Taylor 1998). Dipteran emergence was dominated by

Chironomidae, which accounted for 55% of total insect emergences, followed by

Dolichopodidae 7%, Sarcophagidae 5%, and Culicidae 1%.

Most of adult insects collected in cypress domes were emergent aquatic (93%), while terrestrial adult insects were poorly represented (7%). Dipterans remained the most important family (90%) dominated by Chironomidae (41%) and Culicidae (10%). While emergence rates declined following an initial peak in July, the combined adult insect population (emergent plus terrestrial) surveyed continued to increase progressively through February, with the exception of

January when catch rates may have been affected by the coldest annual temperatures (averaging

15°C - 19°C). After February, the adult insect population declined continuously until the rainy season, which coincided with arrival Neotropical migratory birds.

Relationship between Birds and Insects

Both insect and bird populations varied seasonally, and the responses of bird to local insect populations varied by migratory guild and their residence time in the area. Neotropical migratory birds with short residence times showed only a small non-significant correlation with insect abundances. Conversely, the abundance of winter migrants, which utilize the region for the entire winter, did significantly correlate with both emegent and adult insect abundance combined (r = 0.578, p=0.049, n = 12) (Table 3.1) in the Tampa Bay area from November to

February (Figure 3.7).

Wetlands with short hydroperiods (4-6 months) had both the lowest emergence rates and the smallest bird populations. Insectivorous bird abundance paralleled insect emergence rates and was lowest at sites with the shortest hydroperiod (and lowest insect production) (8.3 insectivores month¯¹), increased at intermediate hydroperiod sites (9.783 insectivores month¯¹) and was greatest with the longest hydroperiods and highest insect production (14.5 insectivores month¯¹). Overall, there was a significant relationship (R² = 0.337, p = 0.038) between insectivore bird abundance andwetland hydroperiod (Figure 3.8). Total bird populations displayed a similar but not significant trend with insect emergence (R² = 0.216, p = 0.09), but a significant relationship with adult insect densities (R² = 0.165, p = 0.049). While resident insectivore populations displayed neither seasonal variation, nor a relationship with local insect populations when compaired directly (Table 3.1), they did however show a statistically significant preference for sites with high annual insect emergence rates (R² = 0.424, p = 0.009) when averaged over the two year period.

Neotropical en-route and breeding migrants behaved similarly and were both present in the Tampa Bay area from February though June during their spring migration. Unlike winter migrants, they only utilize the area for a time short period when insect emergence rates are lowest because most wetlands are dry. During spring migration, wetlands with shortest hydroperiods had the lowest insectivorous bird abundances (28% lower) and emergence rates, while sites with the longest hydroperiods were partially flooded at that time. In summary spring

Neotropical bird migration coincided with the driest months annually in Florida when insect emergence rates were lowest, and adult insect populations declined steadily from February and

May without additional recruitment.

The total insectivorous bird community positively responded to both hydrology and local insect abundnaces. A structural equation model was used to partition the effects of hydrology and insect emergence rates on insectivorous bird populations. The model compared the direct relationship between birds and hydrology then the indirect relationship between hydrology and insects then insects and total insectivorous birds. Positive relationships were found between hydrology and insect emergence, insect emergence and insectivorous birds, and hydrology and insectivorous birds (Table 3.2, Figure 3.9), but total insectivorous birds showed stronger relationships with local insect emergence rates, and hydroperiod than insects did with hydroperiod for the entire durration of the study.

Discussion

Insect emergence rates were highly dependent on the seasonal rain cycle and wetlands with the longest water residence times had the highest levels of annual insect production, as long as the wetland was allowed to dry completely between annual rainfall cycles (Figure 3.6). A

structural equation model (Table 3.2) indicated that longer hydroperiods led to higher rates of aquatic insect production and that in turn corresponded with higher insectivorous bird observations (Table 3.2). Wetlands with longer water residence also were more likely to have higher adult insect populations during the winter time and winter migrants significantly correlated with adult insect populations (Figure 3.7). However, resident birds that were predicted to show the strongest relationship with insect abundances responded at a lower rate than did winter migratory birds.

Winter migrants also displayed a stronger relationship with seasonal food availability in central Florida than neotropical migrants because of their longer residence time in the region.

Winter bird arrival coincided with peak seasonal abundance of adult aerial insects, while spring time Neotropical bird migration coincided with the most food limited time of the year (February

- June) as adult insect populations declined progressively from February through May, possibly associated with large influxes of insect foraging birds and the lack of recruitment of adult insects by aqautic insects due to dry seasonal conditions. Moore and Yong (1971) found that local insect populations could be depleted 67% along the northern Gulf Coast by foraging wood warblers following migration across the Gulf of Mexico. Locally depleted insect communities in central Florida could be critical to the survival of Neotropical migrants arrive in spring after completing a prolonged non-stop flight over open ocean from Cuba and Central America. A flight of such magnitude stretches migratory bird endurance to the limits, forcingbirds to exhaust available fat reserves and diminish muscle mass (Moore and Kerlinger 1987). Birds are extremely energy depleted upon arrival in Florida and must replenish energy reserves before continuing to migrate north, at a time when the adult insect populations of cypress domes and other wetlands are depleted due to low recruitment by emerging aquatic insects that can account

for over 90% of the population. Unfortunately, the later that birds arrive during the spring, the lower the insect populations leading to the need to expend more energy to forage on a limited resource.

Wintering migrants (short-distance migrants) utilize the region during highest adult insect abundance, and a positive correlation with insect abundances suggests that their migration to this area during winter may have evolved in response to seasonal insect patterns. Overall, winter migrant populations were more abundant at sites with higher insect abnundances, similarly to observations of wintering migratory bids and local insect abundances in Jamaica (Johnson and

Sherry 2001) . Great food availability may explain why palm and yellow-rumped warblers have maintained significant populations in this area while other species continue to Central and

South America.

Neotropical migrants poorly responded to insect populations and likely select stopover sites based local environmental cues such as habitat structure and surrounding landscape characteristics over direct food availiability, which might have negative consequences if they consistently select sites appearing favorable like wellfield wetlands but with limited food.

Progressively expanding urban areas with habitat fragmentation and the potential for depleted water tables can only exacerbate the problem for migratory birds. In addition, if climate models are valid, the region will experience progressive drying and associated reduced cypress dome hydroperiod for at least the next 50 to 100 years(Cohen 2010), which considering that wetlands constitute 20% of the central Florida landscape can adversely affect both wintering and

Neotrophical migrant birds.

The abundance of both adult insects and insectivorous bird populations were correlated with wetland hydroperiod length. Sites with the shortest hydroperiods the lowest insect

emergence rates and adult insect abundances and the lowest insectivorous bird utilization by both residents and winter migratory birds suggesting that altered hydrology may drive a trophic cascade that can affect wildlife. Since wellfield areas are some of the few remaining large tracts of land in the Tampa Bay region, implementation of management policies that ensures adequate hydrology for both aquatic insects and birds during migration peaks can have both local and continental implications for the long term sustainability of migratory bird populations.

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Table 3.1. Response of bird guilds to emergent and adult insect abundances. Migratory communities were only compared during the peak migration periods, and data were log transformed prior to analysis. Bird Group Time period Linear Regression

R² p value R² p value

Emergence Adults

Residents All Year 0.115 0.08 0.005 0.334

Neotropical Feb-Jun 0.144 0.07 0.01 0.37

Breeding Feb-Jun 0.083 0.11 0.0001 0.82

Wintering Nov-Feb 0.353 0.05 0.48 0.04

Table 3.2. Structural Equation Model, comparing hydrology and insect emergence to the total insectivorous bird community. Variable Estimate SE Z p Hydrology → Insects 8.55 4.54 1.88 0.060 Insects → Birds 0.029 0.012 2.433 0.015 Hydrology → Birds 0.511 0.217 2.357 0.018

Figure 3.1. Temporal trends in the abundance of insectivorous bird populations averaged across the two years by site. The boxes represent the 1st and 3rd quartiles and the dotted bars represent the 95% confidence intervals.

a. Residents b. Winter Migrants

300 300 200 200 100 100 R² = 0.0003 R² = 0.9568 0 0

0 2 4 6 8 10 12 0 2 4 6 8 10 12 Bird observationsBird Month observationsBird Month

c. Breeding Migrants d. Neotropical Migrants

200 50 100 R² = 0.8806 R² = 0.6248 0 0

0 2 4 6 8 10 12 0 2 4 6 8 10 12 Bird Observations Bird Month ObservationsBird Month

Figure 3.2. Insectivore communities by Migratory Strategy, a) resident insectivores b) wintering migrants c) breeding migrants that have a significant portion that winter in the regions d) neotropical migrants that do not have significant breeding communities in Central Florida

Rainfall

70 35

Water Level 60 30 Insects

50 25 m¯²day¯¹) 40 20

30 15

20 10 Rainfall Rainfall and water level (cm) 10 5 Insect emergence(

0 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Figure 3.3. The relationship between rainfall, water level and insect emergence in cypres wetlands. Left axis includes wetland water level and rainfall levels which were standardized to the figure by Y = rainfall (cm) x 2. Right Axis includes insect emergence rates (m¯² day¯¹).

120

100

Meanwater level (cm) 20

High Intermediate Low

Figure 3.4. Mean water level of wetland groups based on annual hydroperiod. Groups are divided into High (Hydroperiod = 8.5 – 11 months), the Intermediated (Hydroperiod = 6 – 8 months), and Low (Hydroperiod = 4 – 5 months).

Figure 3.5. Insect emergence differences between year 1, when wetlands completely dried prior to the wet season and year 2 when wetlands remained flooded during the dry season.

7000 Year 1 6000 Year 2

5000

4000

3000

2000

1000 Annual emergence Annual ratesyear¯¹ m¯² 0 2 4 6 8 10 12 Months inundated yr¯¹

Figure 3.6. Insect annual emergence versus length of inundation period by year of study.

Winter Migrants 35

25 20 15

10 Bird AbundanceBird 5 0 1 10 100 Insect Abundance (Log scale)

Figure 3.7. Winter migratory bird abundance plotted against log transformed relative abundance of adult insects.

300

280 260 240 220 200 180 160 140 R² = 0.337

120 AnnualMigratory Bird Abundance 100 4 5 6 7 8 9 10 11 Hydroperiod

Figure 3.8. Community abundance of migratory birds over the 2 year study period compared with annual hydroperiod at 13 study wetlands (averaged over the 2 year period).

Insect

Emergence

Hydrology Birds

Figure 3.9. Structural equation model diagram of the relationship between Hydrology Insects and Birds.

CHAPTER FOUR

RESPONSES OF FOREST DWELLING MIGRATORY BIRD COMMUNITIES TO

PROGRESSIVE URBANIZATION IN WEST CENTRAL FLORIDA

Abstract

Urbanization alters native landscapes and negatively impacts native wildlife and often extirpates sensitive urban-avoiding species including many forest-dwelling birds. The principle migratory route in Eastern North America is the Atlantic Flyway that runs down the eastern seaboard before migrants are forest to make jumps across open ocean to Central and South America.

These coastal regions have become highly urbanized and currently account for half of the population who occupy only about 10% of the total land area in the United States. Landscape changes negatively impact bird communities, and urbanization causes over 680 million birds deaths worldwide annually due to collisions with buildings, power lines, and communication towers. Urban landscape changes negatively influence wildlife populations by reducing native habitat, and increased urban development and night time light pollution disrupt annual cycles of species reliant on light for phenological cues. The focus of this study was on how migratory birds respond to urbanization related factors including urban land area, forest area, food availability, and night time light levels. Results indicated that forest dwelling migrants strongly avoid urban areas, declining by 70% in urban wetlands compared with rural sites. Over 90% of

migrants surveyed were insectivorous species, and coincidentally adult insect populations in urban wetlands declined by approximately 40%. Night time light levels, however, were the best predictor of bird communities in cypress dome wetlands, and it was not only migrants that avoided well-lit areas but urban bird populations as well. Protected cypress domes in highly developed urban areas were found to be of little value to Neotropical migratory birds but winter migrants were able to utilize urban wetlands in lower-intensity developed areas closer to the periphery of the urban system. To combat increasing urbanization large continuous tracts protected lands are required if we there is to be any hope of sustaining migratory bird populations in Eastern North America as urbanization continues to increase.

Introduction

The world population has increased from around 1 billion in 1800 to well over 7 billion today (Durand 1977, Keinan and Clark 2012), which has led to the progressive replacement of natural ecosystems of entire regions with urbanized landscapes (Erhlich 1990). This change has brought about increasing mass extinction (Stork, 2010) on the scale of the Cretaceous extinction that ended to age of dinosaurs leaving only the birds as their descendants. (Pimm and Raven

2000, Raup 1986). Since the period of European exploration, expansion, and exploitation (15th century), at least 154 species of birds have become extinct (Pimm et al. 2006) from human hunting or an inability to adapt to profound changes in landscapes.

Of 424 bird species in North America with sufficient data for statistical analysis between

1966 and 2003, 100 species have suffered significant declines including 35 species that have declined over 50% and 6 species over 70% (Peterjohn et al. 1995, Wells 2005). Migratory birds are especially susceptible to environmental changes because they have large geographic

footprints and often travel thousands of kilometers annually from breeding grounds in North

America to wintering grounds in Central and South America (Robbins et al. 1989). The reliance of species on critical habitats is not limited to breeding and wintering grounds, but on critical habitats along migratory routes as well (Mehlman et al. 2005). The Atlantic Flyway is the eastern most of the 4 major North American migratory routes (Lincoln 1939), and it funnels land birds from central and eastern regions of the continent to the Atlantic coast before heading south to staging areas along the Gulf of Mexico, one of the largest geographic barriers crossed by land birds (Alerstam 2001).

Forest dwelling birds in North America can be divided in to three major groups based on migratory strategy which include residents, Neotropical migrants, and short-distance migrants

(Levey and Stiles 1992). Residential non-migratory birds utilize a single home range year round and make no substantial geographic movements annually. Long-distance Neotropical migratory species travel from North America to Central and South America and back biannually, giving them some of the largest annual ranges of any land species on earth, and species often travel thousands of kilometers each direction annually (DeGraaf and Rappole 1995). The short- distance migratory birds are the final group, and they breed in similar regions of North America as Neotropical migratory birds but only travel a short distance south to winter in the southeastern

United States. The three strategies allow for a higher density of bird species to breed in Eastern

North America than the region could support year round and optimize the seasonally available resources (Alerstam 2001).

Along the Atlantic Flyway while en route, birds encounter urban development especially when traveling in coastal areas where birds historically found ample native habitats to rest and refuel during migration. Native coastal habitats have been significantly reduced by urban

development that has resulted in fragmentation of the landscape leaving only remnant habitats that are becoming increasingly isolated (Friesen et al. 1995). Being primarily insectivorous, forest dwelling migratory land birds require large forested tracts with abundant insects during their stopovers, and recently have been forced to rely on continually decreasing forest fragments

(Finch 1991).

Migrations are not acute events but take weeks, during which birds travel through unfamiliar territory and are forced to depend on landscape cues to determine the suitability of habitats at key stopover sites (Nilsson 2013). Most forest dwelling migrants are nocturnal migrants making the majority of their large geographic movements at night. Migrating at night allows for birds to take advantage of daily wind patterns while avoiding diurnal predatory birds such as raptors that migrate along the same routes during the daytime (Alerstram and Lindstrom

1990).

Since most forest dwelling migratory land birds in North America are insectivores or have a significant insect dietary component (Bohning-Gaese et al. 1993), forested wetlands are vital stopover habitats along the flyway. Forested wetlands provide habitat and are preserved at a higher rate than are upland forests and non-forested marsh wetlands thanks to the Clean Water

Act of 1972 (Boyer and Polaski 2004). In Central Florida cypress domes are the most abundant type accounting for 55% of the regions wetland area (Dahl 2005). They are biologically rich habitats with extremely high insect production rates compared to upland forests (Bonter and

Donovan 2009 and Knight 1996). The southeastern United States has the highest concentration of wetlands of the contiguous 48 states and is led by Florida were 20% of the total land area is wetlands (Dahl 2000, Hefner and Brown 1984). However, 40 percent of wetlands in the U. S. have been destroyed since European colonization (Dahl 1990, Dahl 2000, and Tiner 1984).

In the United States approximately 40 % of the population is concentrated in coastal regions that occupy only 10% of the nation’s land area and have the highest densities of wetland area in in the nation (Crowell 2007, and Brown et al. 2005). Encroachment into these regions comes in direct conflict with biologically rich communities endemic to these areas (Saurez et al.

1998). These coastlines act as biological funnels for migrating birds driving them along the

Atlantic coast towards staging areas were they flock together and cross the Gulf of Mexico to

Central and South America (Alerstam 2000, Berthold 2001).

Urbanization poses new dangers to migratory birds in the post industrialized world. Bird strikes of manmade structures account for between 100 and 690 million bird deaths per year worldwide (Erikson et al. 2005). In the United States alone mortality is estimated at 97 million deaths annually from building strikes (Parkins et al. 2015) and 7 million for communication tower/power line strikes (Gehring et al. 2009). Night time light pollution is another threat that has been implicated in the large numbers of migratory bird strikes by disorienting their navigational abilities, especially for species that rely on selective wavelengths of light as a biological compass for navigation (Poot et al. 2008). Artificial light also lures birds to night time lights sources offshore such as oil platforms and large vessels wasting vital fat reserves during flights that already push their energy reserves to the limits (Navara and Nelson 2005). While the attraction of migratory birds to light and well lighted areas and the associated risks are documented (Rich 2005, Poot et al. 2008, and Desholm et al. 2005), little research has been done regarding migratory bird avoidance of night light in general such as urban areas where skyglow creates a dome of light encompassing cities at night.

Insect communities are important food resources for migrating land birds, but the isolation of wetland habitats as urbanization progresses impedes aquatic insect re-colonization of

ephemeral wetland by increasing distances between habitats and decreasing forest cover (Blakely et al. 2006). As urban land area increases it decreases insect diversity in more urban sites and possibly de-values urban wetlands with respect to migrating birds (Donnelly and Marzluff 2004).

Mosquito control is another factor associated with urbanization acting on aquatic insect populations in Central Florida, because mosquitoes pose health risks to humans associated with disease transmission. In order to combat mosquitos most city governments incorporate some kind of mosquito control measures (World Health Organization 1982) and Tampa is no different.

Hillsborough County Mosquito Control continuously monitors local mosquito levels and deploys both adult and larval targeting insecticides that are non-specific and likely negatively influence entire urban wetland insect populations.

The goal of this study was determine how forest dwelling migratory birds respond to urbanization. Since forest dwelling migratory land-birds travel at night and require forest habitats during all stages of their annual cycle, urbanization has the potential to impact migrants on the species level by decreasing the amount of suitable habitats available at key points during their migrations. This study focused on the responses of migratory guilds to environmental factors including insect food forested area within 500 meters, urban area within 500 meters, and urban light pollution (skyglow) associated with anthropogenic night time light pollution. It was predicted that resident and wintering migratory birds, that use the area for sustained periods, would show a greater affinity for local insect populations than would Neotropical Migrants that are simply passing through. Winter migrants were also predicted to have higher populations in low density urban areas than Neotropical migrants because their longer residence time is predicted to allow them time to acclimate and explore urban areas that have adequate insect food availability. Neotropical migrants are predicted to show little relationship with insect

populations and are predicted rely more on landscape and physical features for selection of stopover sites, and were predicted to avoid urban areas and high night time light levels.

Methods

Site Selection

A total of 25 cypress dome wetlands were surveyed monthly for 2 years from February

2012 through January 2014. Sites were selected in 5 subgroups with 5 sites each including 3 wellfields, Cypress Creek (CYC), Morris Bridge Wellfield (MBR), and JB Starkey Wellfield

(STK), and 2 subgroups within the urbanized area north of Tampa Bay: development over 20 years old (old urban (UOLD)), and an area developed post 1990 (new urban new (UNEW)).

Potential wetlands were pre-selected using Arc GIS and the Florida Land Use Cover

Classification System (FLUCCS) map imagery provided by the Florida Geological Data Base

(FGDL 2008) and restricted to sites classified as 6210 cypress wetland with an area between 0.5 and 5 hectares. Age classification of urban development was determined using the estimated construction date of the earliest 25% of buildings within 200 meters of sites and ranged between

0 and 35 years since development.

Land Use

The FLUCCS classification system was used for the large scale classification of land use. The landscape analysis was conducted for distances of 200, 500, and 1000 meters from wetland edges for each site, but reduced to 500 meters because of the lack of significant variation among the three land area classifications. Land area was calculated for forest (both upland and wetland

forest classifications combined) and urban areas (urban development industrial, roads, and land uses classified as other) only.

Bird Surveys

Birds were surveyed where conducted in accordance with normal point count standards during the first 3 hours of daylight and beginning no more than 30 minutes before actual sunrise, the time of greatest bird vocal activity (Bibby 2000). Fixed radius (40 meters) point counts were selected to determine community composition, and surveys were conducted for 5 minutes. Only birds directly utilizing wetlands were counted, those flying above the wetlands where excluded.

From these data a monthly relative abundance value per unit of time was calculated for each site.

The bird counts were first categorized by feeding strategy (with and without an insect dietary component, then according to migratory strategy into residents, Neotropical migrants, and short-distance migrants. The Neotropical migrants were further separated into two subgroups, en-route Neotropical migrants that utilize central Florida only as a stopover area during their migration and breeding Neotropical migrants that have significant breeding populations in

Central Florida according to their ranges in Alderfer (2006).

Insect Surveys

Wetland insect surveys communities where surveyed using floating pyramidal emergent insect traps and malaise block traps for adult insects. Since the total insect community composition does not effectively describe food availability for insectivorous migratory songbirds

(Cooper and Whitmore 1990) due to foraging prey size restrictions, insects greater than 10 mm

in length were excluded from statistical analysis because they too large for consumption by most neotropical migratory songbirds (Johnson and Sherry 2001).

Adult insects where surveyed using malaise traps that passively collects adult insects and therefore estimates relative abundance of adult aerial insect communities (Johnson 2000).

Malaise traps were 1.5m x 2m and deployed for the second year of study from February 2013 through January 2014 alongside emergence traps (Johnson and Sherry 2001). Trapped insects were brought back to the lab euthanized by freezing then sorted and identified using the same methods as emergent surveys.

Environmental Characterization

Wetland water levels where collected monthly during site sampling. Annual hydroperiod was calculated as the period of standing water within wetlands based on the presence of standing water at the deepest insect emergence trap present. When no standing water remained below staff gauges, but pools were located in wetlands, the depth reading was corrected to 0.5 cm of depth to indicate that wetlands were not completely dried. Rainfall and temperature data were obtained from the nearest Southwest Florida Water Management District weather station to each sample location (SWFWMD 2014).

Night time light levels were collected during the migratory period in June and September

2013. A total of 10 light readings were taken at points spaced along the perimeter of each wetland site and averaged for a single value. Light readings were taken during the new moon period after both moon set and at least 1 hour after or before sunrise. Light levels were recorded using a Milwaukee Instruments mi00370 Lux Light Meter, MW700 and displayed at Lux which is a measurement of Luminance and is calculated as Lumens per square meter (Krantz and

Gauthreaux1975).

Analysis

Data were organized into spreadsheets using Microsoft Excel. The open access statistical analysis software program R was used for correlation and regression modeling, and the program

PRIMER 6 was used to conduct community based multi-metric statistical analyses. Seasonality was determined for monthly abundance and the peak migration periods were determined by total abundance of migratory groups. Linear regression models were used to determine community responses to independent variables utilizing logarithmic transformations, and Poisson distributions when necessary to meet the assumptions of normality.

A multiple regression model was used to determine the influence of independent variables on migratory guilds for both richness and abundance including; urban land area within

500 meters of wetland edge, forest area within 500 meters of wetland edge, night time light level, insect emergence rate, and adult insect community. A multi-parametric non-linear analysis was conducted to determine how bird communities of individual sites responded to independent variables using the package Primer 6. The same independent variables were the same as in the multiple regressions but on a community and study wide basis. Independent variables were

normalized, logarithmic transformations were used for species abundance and a presence absence transformation was used for species richness analysis. Similarity analyses were conducted to determine site similarity for bird abundance and species richness. A distance based redundancy analysis was used to display study sites in an ordination using Bray Curtis distances.

A dendrogram was also used to display similarity analyses of wetland bird community abundance.

Results

Over the course of this study a total of 7335 birds were detected representing 94 species.

Resident non-migratory birds accounted for both 66% of all observations (4851) and 40 species.

This group included 8 of the most common species that accounted for 47% total observations and were observed at every study site that included in order of abundance Northern cardinal

(Cardinalis cardinalis), Carolina wren (Thryothorus ludovicianus), tufted titmouse (Baeolophus bicolor), bluegray gnatcatcher, red-bellied woodpecker (Melanerpes carolinus), blue jay

(Cyanocitta cristata), common yellow throat (Geothlypis trichas), and downy woodpecker

(Picoides pubescens). Resident bird populations remained relatively constant throughout the year varying by less than 10% monthly.

Migratory birds made up the remaining 2484 bird detections and represented 54 species.

Migrants were classified into 2 major groups based on their migratory strategy and whether they have significant populations wintering in Central Florida: wintering migrants (short-distance) and Neotropical migrants. The study included 18 species of wintering short-distance migrants, denoted here as ‘wintering migrants’ that utilize the region from November through February before traveling north to their breeding grounds (Figure 4.1). This group included 5 species that

accounted for 89% of the guilds total observations in decreasing importance: Yellow-rumped warbler (Setophaga coronata), Palm warbler (Setophaga palmarum), Gray catbird (Dumetella carolinensis), Pine warbler (Setophaga pinus), and Prairie warbler (Setophaga discolor). No wintering species were found at every study site although of the five species listed above, the

Gray catbird is an edge species and was present at all urban sites and only absent from rural site

191, which is a forested interior wetland with little to no edge habitat. Yellow- rumped, Palm, and Prairie warblers were present at all rural sites but absent from at least one urban wetland.

Neotropical migrants included 36 species that utilize the region from February through

June during spring migration then again in August through October during autumn migration.

The Neotropical group included birds breeding in the region as well as those passing through en- route to seasonal migratory grounds both north and south. Neotropical migrants were subdivided into breeding migrants that have significant breeding populations in Central Florida and en-route migrants that pass through the region on their way to seasonal migratory grounds. Breeding migrants included only 5 species; however, they were the 5 most abundant Neotropical species and included northern parula (Setophaga americana), yellow-throated warbler (Setophaga dominica), white-eyed vireo (Vireo griseus), black-and-white warbler (Mniotilta varia), and yellow-throated vireo (Vireo flavifrons). The remaining 31 species of Neotropical migrants were en-route migrants only stopping in the region long enough to replenish nutrients before continuing on their seasonal migration. As with wintering migrants, Neotropical migrants had no species present at all study sites although Swainson’s thrush (Catharus ustulatus) was observed at all urban sites.

Urbanization

The study focused on factors associated with increasing urbanization predicted to influence bird communities including urban land area within 500 meters of sites, forested area within 500 meters of sites, night time light levels, and insect abundance in wetland sites (Table

4.1). Insect abundance was selected because 98% of migrating birds surveyed within cypress domes (49 of 54 species) have a significant insect dietary component although only 65 of 94 of the total bird species surveyed were categorized as insectivores (75% bird detections).

Urbanization was accompanied by a decline in forest area from 70% of the total land area surrounding rural sites to a mean value of 17% surrounding urban sites. Urban area surrounding sites rose from about 1% within 500 meters of rural sites to 72% surrounding urban sites on average. Urbanization also led to an increase in artificial night time light associated with street lights, buildings and housing that was highest in industrial and commercial areas and lowest in large sprawling newer developed urban areas.

Light levels were calculated in Lux, illuminance calculated as lumens per square meter.

Illuminance is measured on a log scale as follows: moonless starry night = 0.001 lux, full moon

= 0.1 lux, deep twilight = 1.0, cloudy day =1000 and full sunlight = 10000. Light levels surveyed during the new moon phase on cloudless nights indicated that urban sites had significantly higher night time light pollution levels than did rural sites. Light levels where taken

10 times surrounding each study site and the values where averaged for all sites and the average light level at rural sites was approximately 0.03 lux ranging from 0.002 to 0.018. Conversely, the light levels in urban sites ranged between 0.48 and 1.93 lux with an overall average of 0.90 lux (with an intensity similar to that of twilight periods). The mean light level for the Urban Old

site group which is more centrally located in the urban area was 1.19±0.25 lux, while the Urban

New site group located on urban fringe averaged 0.68±0.19 lux.

Bird Trends with Urbanization

Urban development was associated with declining bird populations in cypress dome wetlands during this study. Urban sites had 28% fewer birds per survey (9.92±0.55 birds’ survey¯¹) than rural sites (13.76±0.60 birds’ survey¯¹) (Figure 4.2). The resident bird community declined by -30±2% overall, even though the two most abundance species (Northern cardinal, and Carolina wren) increased with urban development. Neotropical migrants suffered the most pronounced declines, with en-route migrants declining by -65±12%, breeding migrants by -

58±5%, and wintering migrants by -48.5±8%.

This study focused on five factors predicted to influence bird populations associated with urbanization: forest area (within 500 m), urban area (within 500 m), night light levels, emerging aquatic insect rates and adult insect relative abundance. Variables were first addressed individually then combined using a multiple regression model to compare partial r values. Bird communities all positively responded to forest area (Figure 3a), and total abundance showed a strong positive relationship with forest area (R² = 0.46, p = 0.0001), while urban area showed a significant negative trend for the total bird community (R² = 0.59, p = 0.0001) and a negative trend for individual groups (Figure 4.3b). The light levels trended closely with urbanization and rural areas had light levels were consistent with those predicted for a typical cloudless moonless night >0.02 lux. Every bird community negatively trended with light levels consistent with increased urbanization (Figure 4.3c), but showed the most significant trend with the total bird community (R² = 0.62, p = 0.0001).

Insects are an important food source for forest dwelling birds, especially migratory bird groups, which were over 90% insectivores during this study. Because rural wetlands were located within three municipal wellfields and had varying hydroperiods associated with groundwater pumping and natural geology, a comparison was made between hydroperiod and insect emergence, excluding site 191 that had water augmentation, linear regression results indicated emergent insects directly responded to annual hydroperiod (R² = 0.42, p = 0.01)

(Figure 4.4a). Bird communities responded positively with insect emergence on an annual basis though not significant (Figure 4.4b), and there was a positive, but non-significant, trend between hydroperiod and insectivorous bird community on an annual basis (Figure 4.4c). Urban hydroperiod and insect abundance did not show similar relationships, as adult insect communities were 40% lower in urban than rural sites while emergence rates did not differ significantly (Urban = 2010±273 insects m¯² year¯¹, Rural=2093±370 insects m¯² year¯¹). It should be noted that Hillsborough County Mosquito Control records indicate the application of both adult and larval targeting insecticides in all urban areas, though frequency and chemicals used varied and are not well documented among regions.

The Multiple regression model included forest area, urban area, night light level, emergent insects, and adult insects, and though factors and trends were similar, diagnostic tests for collinearity indicate that none violate allowed tolerances for collinearity (none with VIF values above 6.5). Hydroperiod, however, was a potential factor that was excluded because it was collinear with emergent insect abundance. The combined bird community showed a significant negative response (partial r = -0.476, p = 0.03) to nighttime light illumination.

Resident birds had a significant negative response to urban area (partial r = -0.436, p = 0.042).

Migrants were modeled first for the entire year then restricted to the migratory period where the

majority of detection where observed for a specific group. Neotropical migrants showed no significant response for the entire year at the p = 0.05 level but en-route migrants shows a significant negative response at the p = 0.10 level for night time light. Wintering migrants negatively responded to urban light and positively responded to adult insect communities at the p

= 0.10 levels (partial r = 0.392, p = 0.07). When the migratory bird analyses were restricted to guild migratory periods stronger trends were observed. Neotropical migrants had a significant relationship with light level during migration (partial r = -0.317, p = 0.5), while winter migrants positively responded to adult insect abundance (partial r = 0.414, p = 0.03).

A nonparametric multivariate distance based redundancy analysis with Bray Curtis similarity was used to determine the relationship between individual wetland environmental parameters and bird communities. Wetland bird communities were compared for both abundance and richness and analyses (Figure 4.5). The analysis using abundance ordered environmental factors along two distinct planes, with land use along the x axis and insect community along the y axis. Urban and rural sites segregated across the plane with the land use shift and forest and urban area directly apposing one another. Insect communities (emergent and adult) fell along the y axis and influenced had a greater influence on rural sites than urban. A dendrogram indicated a distinct separation between urban and rural sites based on bird communities. It also suggests rural sites in the Starkey group are the most different from those of Cypress Creek and that the

Morris Bridge Road group is and intermediate (Figure 4.6).

The second distance based redundancy analysis used species richness, which is a more conservative indicator of community based responses. This analysis indicated a distinct separation between urban and rural sites as well, with rural sites tightly grouping together into a single cloud while urban sites were spread out. Three factors influenced the distribution of this

ordination including: urban area, night light, and forest area. Insect factors showed very little response at the species level, and community composition responded to urban land area, and night light (Figure 4.7).

Discussion

Urbanization negatively impacts bird communities by reducing natural habitats, and increasing urban development and manmade structures associated with them. During this study urban development led to a 28% decline in total bird populations. Every bird group significantly declined in urban areas where forest area within 500 meters declined from 70.5% to 17.1%, while urban area increased from only 1% in rural areas to 72.1% surrounding urban sites.

Both major migratory groups showed significant declines with urbanization. Winter migratory birds declined overall but did utilize recently developed urban areas that had lower urban intensity, and declined by only 23% in Urban New sites but 74% in Urban Old. The

Urban New and Urban Old did not differ significantly for land use or insect communities but

Urban New sites had lower night-time light levels and were closer to the urban edge and adjacent natural lands. Both sub-groups of Neotropical migrants showed a strong avoidance for all urban areas, declining by 62% in Urban New and by 68% in Urban Old sites.

Species that are not present in urban areas are categorized as urban avoiders, a label commonly associated with large mammals, birds, and reptiles sensitive to human disturbances that disappear from areas with even minimal urban development (McKinney 2002). Urban avoiders are typically residential species but should include some species of forest dwelling migratory bird species as indicated by this study. A likely reason for the strong avoidance by the forest dwelling migratory groups observed here is because as nocturnal migrators they are

deterred by the urban skyglow created by artificial night light that increases ambient light levels to levels similar to twilight. Sky glow could be deterring migratory birds from well-lit areas, forcing them to make long flights around urban areas. This could help explain the precipitous drop in en-route Neotropical migrants utilizing the region that are reliant on environmental cues for stopover sites selection. While migrants declined during the spring migration in urban areas, both en-route and breeding migrant populations seemed absent all together from urban areas during the autumn migration (Figures 4.1c, and 4.1d), either because they are traveling along different migratory routes, are less detectable during this period because they are less vocal or because they are actually avoiding urban areas during this time period.

Winter migratory birds did respond to variability in adult insects (Table 4.2) and positively responded to adult abundance, which may explain their utilization of newer urban

(UNEW) sites the with the highest insect emergence rates during the winter time over older ones

(UOLD). Insect emergence rates where 27% higher in Urban New sites than in Urban Old sites between November and February another factor that could contribute to the difference.

Artificial light appeared to have the greatest influence on bird communities, but artificial light avoidance by migratory birds is poorly represented in the literature. Most publications regarding light focus on the dangers of artificial light attraction by migrating birds by luring them into buildings (Navara and Nelson 2007), communication towers (Gehring and Kerlinger

2009), and off shore drilling rigs (Desholm and Kahlert 2005, Poot et al. 2008) where fatalities associated with night time collisions number in the millions yearly (Kerlinger 2000). This study, however, found that light levels negatively influence bird populations discouraging them from utilizing sites in well-lit urban areas. It was not only migrants that avoided these areas but residents did as well showing the greatest avoidance of the areas with the highest artificial light

levels. Artificial night negatively impacts forest dwelling migratory birds and may force them to travel long distances around well-lit areas and greatly increasing the distances they must travel to reach migratory grounds. While bird communities responded to the other factors mentioned, in the urban setting the two land area factors changed little after initial urbanization, and no strong relationship was seen between urban birds and intra site variation in insect populations but birds did respond steadily to the urban light gradient. When all 5 previously mentioned factors where combined into a stepwise linear regression the best final model included only light level (R² =

0.606, p = 0.0001).

Threats of urbanization on migratory birds are likely the combination of factors including loss of critical habitats and factors associated with urban development. Extinctions directly associated with human encroachment since colonial times in North America are expansive and include some highly charismatic bird species including the only endemic parrot species the

Carolina Parakeet (Conuropsis carolinensis), the largest woodpecker species the Ivory-billed woodpecker (Campephilus principalis), the once most populous wading bird on the Great Planes the Eskimo Curlew (Numenius borealis), and the most populous land bird on the planet at the time of European arrival the Passenger Pigeon (Ectopistes migratorius) (Jackson and Jackson

2007, and Johnson et al. 2010).

A landscape analysis study reported that 58% of the land area in the contiguous United

States no longer supports its native vegetative structure, and poses a threat to over half of the nation’s native ecological communities (Stein and Kutner 2000). Risks for forest dwelling birds increase with the distance they must travel between migratory grounds. This is relevant in the eastern United States where forest area has declined from 70% of the land area in precolonial to less than 40% today (Robbins et al. 1989, Stein and Kutner 2000). Development into a primarily

urban society has led more large buildings and other manmade structures that pose threats to birds migrating at night along their historical flyways.

Urban avoidance limits habitat availability for birds as land continues to be converted from rural into urban landscapes, and it is likely to further restricts viable habitats for migratory bird utilization. The large scale urbanization of the eastern seaboard of North America had converted critical migratory stopover areas from beneficial natural habitats into urban area with value for migratory birds (Wells 2010). Migratory habitats are critical that precede and follow treks across large geographic barrier (Alerstam 2001) such as that Gulf of Mexico to and from

Tampa Bay. Habitat availability at this juncture will likely impact migrant populations in the upcoming century as coastal habitats continue to be converted into urban development. It could the potentially become a limiting factor for migratory bird populations in eastern North America.

At some point even pristine preserves at key locations will no longer be enough to sustain migrant populations because, migrants will deplete insect populations at stopover sites (Moore and Yong 1991) increasing competition and forcing birds to work harder for food and stay longer in suboptimal habitats negatively influencing annual fitness by forcing individuals to arrive later on the breeding grounds and relegate them to suboptimal territories and mates.

In Tampa Bay as migratory birds arrive in spring after crossing the Gulf of Mexico they enter a highly developed region with few large tracts of natural land, and only a few small coastal forested areas. The few large areas of land that are left are primarily lands managed as wellfield areas. The condition of forested wetlands in these areas potentially influences migrant’s abilities to regain lost fat reserves in a timely manner, if impacts from pumping are high they may have negative environmental consequences impacting insect communities by shortening hydroperiods. Drawdown from groundwater pumping decreases hydroperiod and in

turn impacts insect emergence and production. This in turn affects insectivorous bird populations forcing them to forage harder or search for sites with higher food availability.

Therefore migratory birds in rural habitats impacted by anthropogenic activities by in turn be affected by urbanization as well, though not directly but by selecting sites appearing suitable but are degraded in support of urban water needs.

Conclusions

Human encroachment on natural habitats and the utilization of adjacent regions in support of urban systems include factors detrimental to bird communities. Millions of birds die annually as the direct result of urbanization due to building, tower, and car strikes. Urban light pollution creates skyglow that can be seen for miles away at night and is likely impacting nocturnally migrating birds by disrupting flight patterns, and seasonal light cycles. Urban mosquito control is designed to prevent disease but likely has negative consequences for migratory birds by depleting insect food sources, and likely has negative consequences on wintering migratory birds in the region that respond to local insect abundances.

With the world population predicted to reach 11 billion by 2100 (Ramos-Onsins and

Rozas 2002) and destruction of native habitats that will be required to accommodate such a large population many biological communities are in danger of extinction (McKee et al. 2004). It is estimated that 12% of the world’s bird species are threatened by extinction in the next century, and another 12% have small geographic ranges in areas of high human development rabidly destroying their remaining critical habitat (Pimm et al. 2006). Threats for birds cannot always be realized by assessing the breeding and wintering grounds since the majority of annual mortality occurs during the migration itself (Sellett and Holmes 2002) and thus predicted extinction rates

for migratory birds in the next century may not yet be under estimated. If population growth is not soon stymied biological diversity is at great risk and the future landscape is likely to be one lacking many sensitive species or those requiring large geographic ranges.

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Table 4.1. Environmental and biological factors associated with bird community in urban and rural environments.

Percent Percent Breeding en-route Forest Urban Light Emergent Adult Site Winter Neotropic Neotropic area (500 area (500 Level Insects Insects Group Site Residents Migrants Migrants Migrants m radius) m radius) (LUX) m¯² day¯¹ day¯¹

CYC 191 147 58 37 16 99 0 0.008 4.03 3.17 196 262 101 52 20 58 1 0.002 13.22 7.08

199 199 69 38 15 56 0 0.002 7.14 7.83

214 216 82 36 22 80 0 0.002 10.03 2.42

215 234 89 73 15 70 3 0.002 7.94 4.08

MBR 260 242 110 59 15 60 0 0.009 6.58 6.42 264 218 70 59 15 70 0 0.018 9.14 2.42

273 230 63 29 7 86 0 0.18 14.69 7.75

278 160 48 53 13 71 0 0.008 9.31 3.42

293 190 38 32 8 75 2 0.08 4.89 3.75

STK 435 213 70 13 5 64 6 0.002 13.58 3.92 444 188 84 22 9 49 0 0.009 7.92 7.00

485 202 57 33 7 79 0 0.091 7.44 7.33

487 207 57 26 14 59 0 0.002 6.75 4.75

498 157 111 27 12 86 7 0.002 6.19 8.00

Urban 9010 194 41 14 4 3 91 0.48 11.17 3.50 New 9013 186 67 14 4 2 88 0.48 10.56 5.00 (UNEW) 9014 195 67 17 6 3 92 1.36 3.83 3.33 2005 155 61 24 6 21 59 0.38 19.81 5.75

2006 175 50 31 5 40 42 0.3 8.08 2.25

Urban 8013 134 35 18 3 31 57 0.59 8.50 5.42 Old 8070 179 30 9 5 14 79 1.34 6.03 4.08 (UOLD) 7008 238 18 21 11 13 78 0.48 12.39 4.25 7009 160 8 6 1 27 64 1.94 8.11 4.00

7010 170 6 12 1 17 72 1.62 11.56 4.00

Rural 204±8.3 73±5.6 39±4.2 12±1.2 70.5%±7.3 1%±.45 0.03±0.01 8.5±0.09 63.4±6.5

Urban 178±8.8 38±7.2 16±2.3 4.6±0.9 17.1%±2.4 72.1%±7 0.90±0.19 10±0.13 49.9±3.9

Table 4.2. Regression models of bird community responses to factors associated with urbanization. * indicates a significance < 0.05, and + indicates a significance rate >0.10. 107

Night Forest Urban Light Emergent Adult Bird Group m² m² (Lux) insects insects ADJ R² p= Partial Partial Partial r r Partial r Partial r r Birds Total 0.051 -0.24 -0.476* -0.043 0.132 0.662* 0.001 Residents -0.143 -0.436* -0.181 0.323 0.007 0.497* 0.002 Neotropical Breeding 0.168 -0.128 -0.29 -0.036 -0.192 0.395* 0.01 Neotropical en- route 0.083 -0.172 -0.353+ -0.106 -0.173 0.431* 0.006 Wintering Migrants 0.119 0.119 -0.525* -0.208 0.392+ 0.437* 0.006 Seasonal Data For Migrants Neotropical Breeding 0.252 -0.119 -0.197 0.069 0.102 0.336* 0.015 Neotropical en- route 0.204 -0.144 -0.317* -0.082 0.108 0.47* 0.003 Wintering Migrants 0.157 0.274 -0.565* -0.362 0.414* 0.402* 0.009

Total DF for all models df=24

108

10 10 Residents Wintering Migrants 8 8

Rural

Urban 6 6

4 4

BirdsSurveyPer BirdsSurveyPer 2 Rural 2 Urban

0 0

Jul

Jun

Oct

Apr

Sep Feb

Jun

Dec

Jan

Oct

Aug

Apr

Feb Sep

Nov

Dec

Jan

Mar

Aug

Nov

May Mar a. b. May 5 5 Neo - (Breeding) Neo- (En-route)

4 4

Rural Rural Urban 3 3 Urban

2 2

BirdsSurveyPer BirdsSurveyPer 1 1

0 0

M…

Jul Jul

Jun Jun

Oct Oct

Apr

Feb Sep Feb Sep

Dec Dec

Jan Jan

Aug Aug

Nov Nov

Mar Mar c. May d. Figure 4.1. Seasonal Distribution of bird migratory guilds, averaged by urban and rural sites. 1a) the distribution of resident birds annually, 1b) the distribution of wintering migrant birds annually 1c) the distribution of Breeding Neotropical Migrants birds annually, the distribution of En-route Neotropical Migrant birds annually.

109

120 Neotropical

Breeding 100 Winter

Residents

60 Birds year¯¹ site¯¹ 40

0 CYC MBR STK UNEW UOLD

Rural Urban

Figure 4.2. Mean annual bird observations per site by site group.

110

residents residents 200 Forest Area Urban Area wintering wintering 200 breeding

breeding 150

enroute 150 enroute 100 100

50AbundanceBird Bird AbundanceBird 50

0 0 0 500000 1000000 1500000 0 500000 1000000 Forest Area (m²) within 500 m Urban Land area (m²) within 500 m

200 residents Light wintering

breeding

150 enroute

100

Bird AbundanceBird 50

0 0 0.5 1 1.5 2 Light Levels (Lux)

Figure 4.3. Bird migratory guild annual abundance versus a. forest area within 500 m of wetland, b. urban area within 500 m of wetland, c. averaged light level in Lux of area surrounding wetland.

111

5000 100

4000 3000 10 2000

1000 AbundanceBird

Annual Emergence Annual m¯² 0 1 0 5 10 15 1 10 100 Insect Abundance (Log scale) a. Hydroperiod b.

350

300 250 200 150 100

50 Migrant Abundance 0 0 5 10 15 c. Hydroperiod

Figure 4.4. a) Insect emergence calculated annually plotted against wetland hydroperiod for rural wetlands, figure excluded wetland 191 because of permanent impoundment and an insect community more resembling of a lake habitat than a wetland. 4b) Insect emergence rates per visit for rural sites plotted against insectivorous bird abundance. 4c) Total migratory bird abundance plotted against rural wetland hydroperiod

112

Resemblance: S17 Bray Curtis similarity (+d) 20 435 273

498444

)

i r

a 2005 487

l 8013 a t 9013 2006 485 214 196

o Adult Insects

f 0 9010 215 o

9014 293

8070 Emergent Insects 7008

7 .

5 191 Forest

1 199

7009 ,

d 264 260

i f

Urban

% -20 Light 278 7

. 7010

(

b d

-40 -40 -20 0 20 40 dbRDA1 (36.5% of fitted, 36.5% of total variation) Figure 4.5. Bird community abundance distance based redundancy analysis displaying environmental factors including: forest area, urban area, emergent insects, adult insects, and night time light levels.

113

Group average Resemblance: S17 Bray Curtis similarity (+d) 50

m i S 80

100

0 3 0 9 0 8 3 4 5 6 1 9 6 5 4 0 8 8 4 3 5 7 3 5 4

1 1 7 0 1 0 1 1 0 0 9 9 9 1 6 6 7 9 1 9 8 8 7 3 4

0 0 0 0 0 0 0 0 0 0 1 1 1 2 2 2 2 4 2 2 4 4 2 4 4

7 8 8 7 9 7 9 9 2 2 Samples Figure 4.6. Dendrogram displaying wetland bird community resemblance among study wetlands.

114

Transform: Presence/absence Resemblance: S17 Bray Curtis similarity 10

9010 )

n 9013

o 264 i

t 191

a i

r 498 2005 a

v Urban 485

l 2006 7008 a

t 8013

o t

196 f 0 Forest214

o 273 9014 278215260199

% 435 293444 5

. Emergent Insects487

d 8070

e Adult Insects

% 7010

6 -10 .

2 7009

(

2 A

D Light

b d

-20 -20 -10 0 10 20 30 dbRDA1 (70.8% of fitted, 25.5% of total variation) Figure 4.7. Species richness distance based redundancy analysis displaying Bray Curtis similarity and environmental factors including: forest area, urban area, emergent insects, adult insects, and night time light levels.

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CHAPTER FIVE

GENERAL CONCLUSIONS

Human activity has altered much of the planets land area, altering entire landscapes to conform to standards considered desirable and suitable for high density human habitation. The urbanization process tends to homogenize and degrade natural areas, depleting natural resources and making the landscape inhospitable to sensitive and specialist species (Marzluff and Ewing

2001). Land utilization favors upland habitats that are developed at a higher rate while wetland and aquatic areas are often found undesirable and historically have been avoided, drained, or viewed as wastelands suitable only for waste and sewage.

Landscape degradation includes construction buildings and other manmade structures, destruction of native habitats, declines in connectivity, and degradation of water resources. The goal of this study was to determine how anthropogenic activities impacted cypress dome wetland emergent insect communities, and how insect emergence and abundances related forest dwelling bird communities and migratory cycles. Urbanization and groundwater manipulation degrade natural habitats, and as urbanization progresses entire landscapes are altered to conform to standards required for human habitation. Anthropogenic activities are not restricted to urban areas themselves, but include adjacent non-urban areas needed for support including agriculture and additional water sources. In Central Florida groundwater pumping is the primary water source for agriculture and municipal water supplies and is needed to support the urban

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population of near 4 million in the Tampa Bay region of Central Florida (U.S. Census Bureau

2010). Excessive pumping to support of the area has led to competition for water rights after the population of Pinellas county Florida increased rapidly during the 1960’s and 1970’s, and in order to match the needs of the growing population large quantities of water where extracted leading to saltwater intrusion of the local aquifer. So to keep up with the demand Pinellas

County began pumping water from adjacent Pasco and Hillsborough Counties which led to environmental degradation in these adjoining counties that directly resulted in a reduction on the local water tables surrounding pumping stations. Declines altered native hydrology of nearby wetlands, including cypress domes, causing environmental stress on wildlife and vegetative communities and increased tree mortality in cypress domes that allowed for wetland intrusion by upland species. Upon realization of this degradation, legislation was enacted in the 1990’s to implement standards for reduction of groundwater withdrawal rates and to seek alternatives to the high levels of groundwater pumping.

While the effects of groundwater pumping have been well studied on vegetative communities in the region (Carr et al. 2006, and Haag et al. 2005) little had been done with how pumping effects wetland wildlife communities. The goal of this study was to determine how decreases to hydroperiods impact local insect and bird communities, and to determine if they responded to changes in water levels and annual hydroperiod. Results indicated that hydroperiod reductions did lead to a decline in both total insect emergence and insect diversity, with the sites having the shortest annual hydroperiods also recording the lowest annual emergence rates, and excluded some groups of winter insects including the Chironomidae genera Tanytarsus and

Pseudochironomus. The decrease in hydroperiod also meant that groups with prolonged aquatic

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larval stages did not have a sufficient inundation period to complete their life cycles (Anisoptera, and Ephemeroptera) so wetlands where not suitable habitats for these groups.

Decreased insect emergence rates led to fewer recruits contributing to the adult insect population which were an important factor in predicting the presence of wintering migratory birds. Reducing the insect replenishment rates early in the dry season led to lower adult insect abundance in wetlands that dried early, especially later in the season. Winter birds utilize the region from November through February during the first half of the dry season and positively correlated with adult insect abundance, suggesting that they likely seek out sites with the higher adult insect populations to forage, concurrent with the findings of Johnson and Sherry who focused on how warbler population responded to variation in local insect populations in Jamaica

(2001).

While the relationship between groundwater pumping, insect populations and wintering migratory birds is fairly straight forward the relationship between insects and Neotropical migratory birds is less evident. Neotropical migrants travel through Central Florida during their spring migration from February through June following the exodus of the wintering migrants and arrive late in the dry season when most wetlands have dried out already and insect replenishment rates from emergent insects are at their lowest. This is quite possibly the worst possible time for these birds to migrate through this region relative to insect food availability, and could possibly prove the most stressful point along their entire migration. A large number of Neotropical migrants arrive in the area following a non-stop journey from Central and South America after which birds are depleted of fat reserves and require nourishment before they can continue on their migrations (Alerstam 2001, and Moore and Kerlinger 1987). At this point it is vital that birds be able to recover lost fat reserves and continue on with their migration as fast as possible

118

because time constraints during spring migration favor birds that can make the migration the fastest and arrive on breeding grounds and establish territories first, and this is the reason why the spring migration is much shorter than fall migration (Bauchinger and Klaassen 2005).

During spring, the speed and duration of the migration are more dependent on the ability to procure food and deposit fat than on flight speed. This is also a time of heavy inter and intraspecific competition for food resources. This study found a 76% decline in adult insect populations between, February and May, which is in agreement with previous research indicating the depletion of adult insects by Neotropical migratory birds along the northern Gulf Coast of

Alabama and Mississippi (Moore and Yong 1991).

Many species of Neotropical migrants are forest dwelling species that are described as urban avoiders because of their underrepresentation in residential areas (McKinney 2002).

During this study Neotropical migrants favored rural sites and declined by over 70% in the most developed urban areas. The strong avoidance of urban wetlands by Neotropical migrants restricts the total habitat available to these communities to only a few remaining large tracts of protected lands because of heavy urbanization in the region. Consequently, the majority of the remaining large land tracts are protected primarily as sources for groundwater pumping.

Neotropical migrants utilizing these wellfields showed less of a response to local insect abundances than did winter migrants, likely because they select sites based on landscape cues rather than actual food availability. Evidence that migration routes and site selection criteria are genetically programed has been posed by Jenni and Schaub (2003). Birds selecting sites with low insect densities are forced to travel further and forage longer and harder than birds that select sites with high food availability (Moore and Yong 1991). Since data indicated a precipitous decline in insect abundance from February through May, it is likely that the heavy influx of

119

Neotropical migrants depletes the adult insect populations that are already at their lowest annual levels. With available land area continuing to decline across Florida in association with the rapid population increase (11 million in 35 years, U.S. Census Bureau 2015), less and less habitats are available for migratory birds to utilize.

Urbanization led to lower migratory bird populations and adult insects in cypress domes.

Insect emergence rates did not significantly differ between rural and urban areas, but the adult insect populations declined by 40% in urban wetlands. A possible reason for this urban insect decline that was not directly addressed during this study was mosquito control and information from the Hillsborough County Mosquito Control indicated that insecticides were used in all urban areas studied. The insecticides directly targeted Culicidae and Chironomidae members which accounted for the majority of adult insects collected during this study but the insecticides are not specialized and by controlling for these two groups, the mosquito control measures are likely negatively influencing both target and non-target insect populations and negatively influencing migratory birds’ abilities to procure food in urban wetlands.

Potential factors influencing bird communities other than insect food availability included forest connectivity, urban land use, and night time light pollution. All three of these factors directly correlated with every bird group surveyed, but a multiple regression analyses indicated that light levels where the best predictor of bird community composition. Both residential and migratory birds negatively responded to increased night time light levels surrounding sites.

The danger of urban areas on migratory birds is compounded by poor food availability, decreased habitat, increased urban structures, and environmental disturbances including noise and light pollution. Building strikes alone cause and estimated 97 million bird deaths a year in the United States (Parkins et al. 2015) while communication tower strikes account for another 7

120

million (Gehring et al. 2009). An estimate by the USDA Forest Service estimates even higher rates somewhere between 500 million and 1 billion bird mortalities each year associated with anthropogenic structures in the United States alone (Erikson et al. 2005).

Looking forward, bird populations are likely to continue to decline as urban development increases unless appropriate measures are taken to preserve large tracts of land capable of supporting large numbers of migratory birds at key stopover points between Eastern North

America and Central/South America. Bird declines will continue until development slows or species are able to reach an alternate stable state where breeding habitat, wintering habitat, and migration resources are sufficient to maintain what migratory bird populations are left. New communities are likely to have much lower diversity than current and historic ones and lower than any level monitored since the inception of the North America Breeding Bird Survey. The most sensitive species are likely to disappear with the current trajectory, leaving resources for the more tolerant species to utilize as populations eventually stabilize in the future.

121

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hydrology and the landward extent of hydric soils in west-central Florida, USA cypress

domes. Wetlands, 26(4), 1012-1019.

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mortality from anthropogenic causes with an emphasis on collisions. USDA Forest

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APPENDICES

Appendix A. Malaise Traps Adult Insect Data.

Order Family Genus CPR MBR STK UNEW UOLD Diptera Agromyzidae 1 2 1 1 Diptera Anthomyiidae 3 Diptera Aulacigastridae 4 Diptera Bibionidae 1 Diptera Cecidomyiidae 17 22 39 29 24 Diptera Ceratopogonidae 2 8 19 14 3 Diptera Chaoboridae 4 3 8 1 Diptera Chironomidae Ablabesmyia 1 3 Diptera Chironomidae Chironomus 3 2 4 5 4 Diptera Chironomidae Cryptochironomus 3 3 1 2 Diptera Chironomidae Goeldichironomus 1 Diptera Chironomidae Parachironomus 1 Diptera Chironomidae Polypedilum 7 7 11 8 7 Diptera Chironomidae Pseudochironomus 76 24 76 8 22 Diptera Chironomidae Tanytarsus 3 3 2 6 9 Diptera Chironomidae (blank) 48 66 56 73 51 Diptera Chironomidae Total 140 107 154 103 93 Diptera Chyromyidae 2 2 Diptera Cicadellidae 3 Diptera Cicidomyiidae 5 Diptera Clephariceridae 1 Diptera Culicidae Aedes 6 3 2 1 1 Diptera Culicidae Anopheles 13 9 5 14 29 Diptera Culicidae Coguillettidia 2 Diptera Culicidae Culex 2 2 3 1 Diptera Culicidae Psorophora 2 Diptera Culicidae Uranotaenia 4 1 5 6 3 Diptera Culicidae Urotaenia 16 Diptera Culicidae (blank) 3 1 3 Diptera Culicidae Total 27 18 17 22 52 Diptera Deuterophlediidae 1

124

Appendix A. (continued)

Order Family Genus CPR MBR STK UNEW UOLD Diptera Dolichopodidae 19 25 48 8 8 Diptera Dryomyzidae 1 Diptera Empididae 1 19 1 Diptera Ephydridae 2 4 5 Diptera Hymenoptera 1 Diptera Lonchaeidae 5 2 Diptera Milichiidae 1 Diptera Muscidae 1 1 Diptera Mycetophilidae 2 2 Diptera Pachyneuridae 1 Diptera Phoridae 1 Diptera Psilidae 1 Diptera Psychodidae 1 1 Diptera Sarcophagidae 12 15 15 10 5 Diptera Scathophagidae 1 Diptera Sciaridae 23 24 9 20 6 Diptera Sciomyzidae 2 1 4 1 Diptera Simulidae 2 1 2 Diptera Stratiomyidae 1 Diptera Tabanidae 1 5 1 2 1 Diptera Tanypedidae 1 1 Diptera Tephritoidea 2 Diptera Thaumaleidae 4 Diptera Tipulidae 1 5 7 3 Anisoptera 1 Coleoptera 5 4 1 2 Hemiptera 7 3 2 4 7 Hymenoptera 8 32 7 2 15 Lepidoptera 3 4 14 10 Neuroptera 1 1 1 Orthoptera 1 2 2 Total 291 285 370 254 242

125

Appendix B. Aquatic Dipnet Survey Insect Data.

Group Family CYC MBR STK UNEW UOLD Anisoptera Corduliidae 8 Anisoptera Libellulidae 7 11 17 2 8 Blattodea 8 Chilopoda 1 Coleoptera Dytiscidae 6 1 4 3 Coleoptera Elmidae 4 1 Coleoptera Gerridae 1 2 Coleoptera Gyrididae 2 Coleoptera Hydrophilidae 1 Coleoptera Lampyridae 1 Coleoptera Noteridae 23 2 1 Coleoptera Psephenus 1 Coleoptera Scirtidae 5 4 3 1 1 Culicidae 12 Diptera Ceratopogonidae 3 1 1 Diptera Chaoboridae 1 2 Diptera Chironomidae 69 67 89 51 111 Diptera Culicidae 2 2 Diptera Dolichopodidae 1 1 1 Diptera Ephydridae 1 Diptera Tabanidae 1 Ephemeroptera Caenidae 9 3 1 12 4 Ephemeroptera Siphlonuridae 2 1 Gammaridae 8 2 Hemiptera Veliidae 1 Hemiptera Belostomatidae 7 4 13 3 Hemiptera Gerridae 1 1 1 1 Hemiptera Hydrometridae 1 Hemiptera Macroveliidae 1 Hemiptera Mesoveliidae 1 Hemiptera Naucoridae 5 Hemiptera Notonectidae 1 7 5 Hemiptera Veliidae 4 Hirudinea 1 Lepidoptera 1 Megaloptera Corydalidae 1

126

Appendix B. (continued)

Group Family CYC MBR STK UNEW UOLD Anisoptera Gomphidae 1 Anisoptera Libellulidae 1 6 Tipulidae 1 Tricoptera Leptoceridae 1 Zygoptera Coenagrionidae 3 4 Zygoptera Lestidae 5 1 1 Total 128 126 194 74 149

127

Appendix C. Insectivorous Bird Community.

Site Group CPR MBR STK Migratory 19 19 19 21 21 26 26 27 27 29 43 44 48 48 49 Status Common Name 1 6 9 4 5 0 4 3 8 3 5 4 5 7 8 Neotropical En Route Acadian Flycatcher 2 1 1 3 American Redstart 3 1 1 1 2 2 Baltimore Oriole 1 Blackburnian Warbler 1 2 1 1 1 Blackpoll Warbler 1 1 2 1 3 1 1 1 2 Black-throated Green Warbler 1 1 Blue Grosbeak 1 Cape May Warbler 1 2 2 3 3 5 1 1 2 Eastern Kingbird 1 Great Crested Flycatcher 4 5 1 2 1 2 3 2 1 2 1 4 2 4 3 Indigo Bunting 1 2 1 1 Kentucky Warbler 1 1 Louisiana Waterthrush 1 1 Magnolia Warbler 1 2 Nashville Warbler 1 Northern Waterthrush 1 1 Orange Crowned Warbler 1 2 2 1 2 Philadelphia Vireo 1 1 Prothonotary Warbler 1 Red-eyed Vireo 4 3 1 5 1 4 1 2 8 2 1 Scarlet Tanager 2 1 1 2 1 Summer Tanager 1 Swainsons Thrush 1 1 1 1 1 1 1 1 1 Swainsons Warbler 1 1 1 1 Worm eating warbler 2 2 2 1 2 1 Yellow Warbler 1 1 1 Yellow-billed Cuckoo 1 Yellow-breasted Chat 1 1 Neotropical En Route Total 16 20 15 22 15 15 15 7 13 8 5 9 7 14 12

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Appendix C. (Continued)

Site Group CPR MBR STK Neotropical Breeding Black and White Warbler 1 2 7 7 4 6 3 4 2 4 3 3 3 4 Northern Parula 23 20 17 13 21 32 30 7 33 13 6 9 12 14 9 Yellow-throated Warbler 3 2 2 2 10 5 12 1 5 1 6 4 4 White-eyed Vireo 8 26 11 16 27 15 12 5 6 10 2 4 13 7 8 Yellow-throated Vireo 2 2 1 5 8 8 6 2 9 2 1 2 2 Neotropical Breeding Total 37 52 38 36 73 59 59 29 53 32 13 22 33 26 27 Reside nt Blue Jay 14 15 10 6 12 12 6 8 6 7 4 5 12 1 8 Blue-gray Gnatcatcher 13 12 22 22 17 25 27 11 30 26 12 11 17 7 4 Brown-headed Nuthatch 1 2 1 Carolina Chickadee 10 15 13 4 15 20 14 23 11 12 11 15 9 18 11 Carolina Wren 26 39 22 36 37 28 52 33 20 28 37 33 34 24 45 Common Yellowthroat 14 11 36 13 2 1 32 5 8 31 20 13 21 13 Downy Woodpecker 7 12 13 6 8 8 10 6 6 7 2 7 11 9 6 Eastern Bluebird 1 Eastern Towhee 1 21 15 5 19 10 7 32 17 10 15 4 19 3 Hairy Woodpecker 1 1 1 Northern Cardinal 26 40 34 43 34 38 36 27 45 39 36 35 34 28 Northern Flicker 1 Northern Mockingbird 1 1 Pileated Woodpecker 8 14 8 6 4 9 5 6 1 4 6 7 11 3 Red-bellied Woodpecker 11 21 16 11 19 16 9 11 13 15 10 17 17 12 8 Red-winged Blackbird 2 1 1 Tufted Titmouse 18 20 33 23 28 27 33 28 28 17 17 14 18 24 16 13 22 16 19 21 19 20 22 15 18 17 18 17 18 14 Resident Total 5 5 4 0 5 1 3 1 2 5 8 2 7 1 6 Wintering Migrant American Robin 1 5 5 4 1 5 19 2 11 Blue-headed Vireo 1 1 1 Chipping Sparrow 1 1 Eastern Phoebe 6 9 6 4 4 3 2 1 1 1 2 6

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Appendix C. (Continued)

Site Group CPR MBR STK Gray Catbird 7 5 9 10 2 13 11 3 4 8 8 12 8 12 Hermit Thrush 1 1 1 Ovenbird 1 1 1 1 Palm Warbler 14 8 22 15 22 35 17 16 9 15 15 12 8 10 14 Pine Warbler 5 5 6 5 11 2 13 4 6 9 16 17 10 25 1 Prairie Warbler 6 6 8 12 8 9 9 1 9 1 1 3 6 1 8 Ruby-crowned Kinglet 1 1 1 1 Swamp Sparrow 9 2 1 Yellow-bellied Sapsucker 1 2 2 1 1 2 Yellow-rumped 3 Warbler 28 4 23 25 32 37 21 20 21 12 25 24 12 14 38 Wintering Migrant 9 10 11 Total 56 3 69 82 87 5 70 63 48 38 67 83 57 57 1 3 Grand 9 30 33 39 37 34 32 26 26 26 29 27 27 29 Total 244 0 8 0 0 0 7 0 6 3 3 6 4 8 6

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Appendix D. Emergent Insect Community.

Site Group CPR MBR STK 19 19 19 21 21 26 26 27 27 29 43 44 48 48 49 Group Family 1 6 9 4 5 0 4 3 8 3 5 4 5 7 8 Dipter a Agromyzidae 6 Anthomyiidae 3 4 1 Asteiidae 1 Athericidae 1 Bibionidae 7 1 Calliphoridae 3 3 Cecidomyiidae 1 9 8 15 9 10 1 17 18 5 3 4 11 3 8 Ceratopogonid ae 6 3 1 5 3 12 4 1 12 29 4 1 Chamaemyiida e 1 Chaoboridae 1 28 16 16 11 6 1 13 3 15 1 3 7 7 20 10 13 15 19 10 13 Chironomidae 64 1 83 1 99 7 2 2 6 48 54 72 75 90 1 Chloropidae 1 1 1 Chyromyidae 1 1 3 Cryptochetidae 1 Culicidae 4 25 4 4 8 8 16 20 1 1 11 1 Dolichopodida e 11 11 8 31 20 13 16 23 17 32 9 21 7 11 15 Dryomyzidae 5 1 Emphydridae 3 5 Empididae 3 1 3 1 Ephydridae 1 1 1 3 1 7 Hybotidae 1 Lauxaniidae 4 Milichiidae 1 Muscidae 3 1 1 3 8 1 Nemistrinidae 1 Ochlerotatus 2 Phoridae 1 1 1 Ptychopteridae 1 2 Sarcophagidae 3 8 7 5 8 5 1 37 24 4 7 44 11 11 16 Scathophagida e 1 Sciaridae 1 4 4 1 12 3 1 Sciomyzidae 1

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Appendix D. (continued)

Site Group CPR MBR STK 20 Simulidae 1 4 4 1 4 3 3 1 Stratiomyid ae 1 3 1 1 Syriphidae 1 1 1 3 1 Tabanidae 1 1 3 Tachinidae 1 Tanypezida e 1 1 4 4 3 1 Thaumaleid ae 1 1 Tipulidae 1 3 5 4 2 6 3 1 Blattodea 1 1 Coleoptera 3 8 5 9 1 3 5 1 3 5 1 3 Ephemeroptera 3 5 11 5 1 4 3 1 3 7 3 5 Hemiptera 9 8 10 17 9 2 12 5 3 7 6 3 1 7 3 Hymenopte ra 3 1 3 1 12 6 5 4 4 4 5 Lepidopter a 1 3 1 5 8 3 1 9 3 3 Megalopter a 1 Neuroptera 1 1 1 4 2 4 4 Odonata 1 1 3 1 6 Trichoptera 3 Grand 11 32 17 23 20 21 24 34 22 13 32 18 17 15 19 Total 1 8 2 9 0 6 1 0 3 1 3 5 9 9 2

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