Dynamics of a Problematic Vulture Roost in Southwest Florida and Responses of Vultures to Roost-Dispersal Management Efforts

Home , Cinereous vulture, Communal roosting, Old World vulture

DYNAMICS OF A PROBLEMATIC VULTURE ROOST IN SOUTHWEST FLORIDA AND

RESPONSES OF VULTURES TO ROOST-DISPERSAL MANAGEMENT EFFORTS

A thesis

Presented to

The Faculty of the College of Arts and Sciences

Florida Gulf Coast University

In Partial Fulfillment

Of the Requirement for the Degree of

Master of Science

Betsy A. Evans

2013

APPROVAL SHEET

The thesis is submitted in partial fulfillment of

the requirements for the degree of

Master of Science

______

Betsy A. Evans

Approved: December 2013

______

Jerome A. Jackson, Ph.D.

Committee Chair / Advisor

______

Edwin M. Everham III, Ph.D.

Committee Member

______

Charles W. Gunnels IV, Ph.D.

Committee Member

The final copy of this thesis has been examined by the signatories, and we find that both the content and the form meet acceptable presentation standards of scholarly work in the above mentioned discipline. iii

ACKNOWLEDGMENTS

First and foremost I thank my thesis advisor, Dr. Jerry Jackson, whose support, assistance, and interest throughout the whole process was vital in the preparation and completion of this project.

I am grateful to my committee members, Dr. Billy Gunnels and Dr. Win Everham, who provided statistical guidance and vital assistance in the interpretation and editing of the project.

I am appreciative to the Department of Marine and Ecological Sciences and the

Department of Biological Sciences at Florida Gulf Coast University for their support and encouragement during the completion of my degree.

Additionally, I thank the Guadalupe Center of Immokalee for allowing me to conduct research on their property and providing valuable information during the project. A special thank you to the Ding Darling Wildlife Society for their generosity in providing supplemental funding for the project.

I would like to thank my family and friends for their encouragement and positivity while

I completed my thesis work. And last, but not least I would like to thank my husband, Lucas

Halverson, whose assistance with data collection was invaluable and whose positivity gave me the strength to finish my graduate degree. iv

ABSTRACT

North American populations of Black Vultures (Coragyps atratus) and Turkey Vultures

(Cathartes aura) are steadily increasing and their ranges are expanding, and both species are common in southwest Florida. Success of these species in the United States has led to a rise in conflicts between humans and vultures and an increased need for effective vulture management.

The occurrence of a problematic vulture roost at the Guadalupe Center of Immokalee, an early childhood education center in southwest Florida, was the focal point for a conflict between humans and vultures. The Center had up to 250-300 vultures on their property on a daily basis throughout most of the year. Vultures were observed perching on the Center building and surrounding structures, as well as using an associated retention pond for bathing and drinking, and adjacent mowed areas for social interactions.

The primary objective of this study was to evaluate and determine site-specific solutions to a vulture roost location problem. In order to provide site-specific solutions to vulture roost problems, an understanding of vulture behavior and roost habitats used by vultures was essential to determine why the Guadalupe Center and areas surrounding it were attractive as a roost site. A secondary objective included the evaluation of management techniques that were initiated by the

Center and were not site-specific. The overall goal was to evaluate vulture management techniques available, to reduce and disperse the vultures on the property, and reduce vulture- caused damage.

The Guadalupe Center roost was compared to 26 vulture roosts in the United States. Of the 15 roosts observed in Florida, all were associated closely with water suggesting an importance of water to vulture roost location. Air currents, such as obstruction currents were v present in over 70% of the roosts analyzed suggesting the importance of air current production to the proximity of roost sites.

After the implementation of site-specific management techniques, the total population of vultures on the property decreased significantly. The total population of vultures did not decrease significantly after the initiation of non-site-specific management techniques.

The areas of the property the vultures occupied differed between pre- and post- management. During roof-area management, vultures used the forested area north of the Center’s property more often than expected and used the fences, pond, and building less often than expected, suggesting that site-specific management efforts were effective at dispersing the birds and reducing their impact on the property. Non-site-specific Center-initiated management did not have a long-term effect on the population; birds readily habituated to the strategies (deployment of vulture carcasses and pinwheels) and were observed more often than expected on all areas of the Center’s property.

The behavior of the birds at the Guadalupe Center did not differ significantly when comparing pre-management to any management strategy suggesting that management did not prevent vultures from engaging in behaviors essential for survival.

Consistency and persistency are keys to effectively managing a problematic vulture roost.

When the Center initiated non-site-specific management techniques, the vultures did not alter their use of the property. Since the management initiated by the Center was not consistent, vultures were able to readily habituate to the deterrents. Management of vultures should be a site-specific gradual process. Understanding behavior and roost habitat parameters is essential to developing effective management strategies for vultures. vi

TABLE OF CONTENTS

ACKNOWLEDGMENTS ...... iii

ABSTRACT ...... iv

TABLE OF CONTENTS ...... vi

LIST OF FIGURES ...... viii

LIST OF TABLES ...... x

INTRODUCTION ...... 1

MATERIALS AND METHODS

Study area ...... 5

Roost habitat characteristics...... 11

Pre-observational control data collection ...... 12

Management techniques ...... 15

Post-management data collection ...... 23

Data analysis ...... 23

RESULTS

Roost habitat characteristics...... 25

Guadalupe Center roost composition ...... 28

Management techniques ...... 30

Behavior ...... 43 vii

DISCUSSION

Guadalupe Center vulture roost composition...... 45

Vulture response to management efforts ...... 45

Use of noise, visual, and chemical repellants in vulture management ...... 47

Role of roost habitat characteristics in vulture management ...... 51

Importance of vulture behavior in management plans ...... 53

Community activities contributing to vulture roost problems ...... 55

What made the Guadalupe Center attractive as a roost site? ...... 57

Need for effective vulture management ...... 59

APPENDIX A

Black and Turkey vulture species information ...... 62

APPENDIX B

Problems associated with vulture use of the Guadalupe Center property ...... 69

APPENDIX C

Ineffectiveness and limitations in the implementation of the management

techniques of the Guadalupe Center roost ...... 78

APPENDIX D

Future management suggestions for the Guadalupe Center roost site and other

problematic vulture roosts...... 83

LITERATURE CITED ...... 87 viii

LIST OF FIGURES

Figure 1: Map of study area in Collier County, Florida ...... 6

Figure 2: Aerial photograph of Immokalee, Florida ...... 8

Figure 3: Aerial photograph of the Guadalupe Center ...... 10

Figure 4: Types of vulture behavior observed at the Guadalupe Center ...... 14

Figure 5: Fence management ...... 17

Figure 6: Pond management ...... 18

Figure 7: Water pump management ...... 19

Figure 8: Mowed area management ...... 20

Figure 9: Roof and awning management ...... 21

Figure 10: Light pole management ...... 22

Figure 11: Vulture population at Guadalupe Center ...... 28

Figure 12: Average number and age of Black Vultures during pre- and

post-management ...... 29

Figure 13: Average number of Black Vultures during pre- and post-management...... 32

Figure 14: Average number of adult Black Vultures during pre- and

post-management ...... 33

Figure 15: Average number of immature Black Vultures during pre- and

post-management ...... 34

Figure 16: Average number of Black Vultures during pre- and

pond-area management ...... 35

Figure 17: Average number of Black Vultures during pond-area and

roof-area management ...... 36 ix

Figure 18: Average number of Black Vultures during roof-area management and management

disruption...... 37

Figure 19: Average number of Black Vultures during management disruption and Center-

initiated management ...... 38

Figure 20: Dispersion of Black Vultures on the Guadalupe Center property ...... 39

Figure 21: Proportion of Black Vultures engaged in behaviors at Guadalupe Center ...... 44

Figure 22: Fence located at property across from Guadalupe Center ...... 58

Figure 23: Black Vulture using obstruction current at Guadalupe Center ...... 70

Figure 24: Vulture use of Guadalupe Center roofs ...... 72

Figure 25: Vulture use of light poles and light shields ...... 73

Figure 26: Vulture damage to air-conditioning units at Guadalupe Center ...... 74

Figure 27: Vulture use of mowed areas at Guadalupe Center ...... 75

Figure 28: Water pump at the Guadalupe Center ...... 76

Figure 29: Water created by excessive irrigation at the Guadalupe Center ...... 77

Figure 30: Fence damage at the Guadalupe Center ...... 80

LIST OF TABLES

Table 1: Habitat characteristics and composition of vulture roosts ...... 26

INTRODUCTION

Vultures are part of the most threatened avian guild in the world, the avian scavengers

(Sekercioglu 2006). Two of the seven species of New World vultures (i.e. California Condor

(Gymnogyps californianus) and Andean Condor (Vultur gryphus)) are currently listed as threatened or endangered, and twelve out of the sixteen Old World vulture species are listed as vulnerable, threatened, or endangered (IUCN 2012).

In contrast to the many species of vultures that are experiencing population declines,

Black Vulture (Coragyps atratus) and Turkey Vulture (Cathartes aura) populations in the

United States are increasing throughout most of their range (Avery 2004). Data from migration counts, Christmas Bird Counts (CBC), and Breeding Bird Surveys (BBS) suggest that Black and

Turkey vulture populations have increased significantly in many areas across the eastern United

States (Farmer et al. 2008).

While urban development has been cited as a growing threat to birds across the world,

Black and Turkey vulture population increases appear to be partially explained by vultures’ ability to take advantage of urbanization. There are clearly some adaptations of vultures that allow these birds to take advantage of human-caused habitat alterations (Avery 2004, Mandel and Bildstein 2007). For example, an increased albedo of the Earth’s surface (e.g., global warming, clearing of forests, construction of cities, roads, and parking lots) has created an increasing frequency in both time and space of anthropogenic thermals, which vultures use for energy-efficient flight (Mandel and Bildstein 2007), and contributed to the northward range expansion of both species (Mossman 1991, Sauer et al. 1997). Vultures have also adjusted to human-altered landscapes by taking advantage of the architecture of many anthropogenic structures, such as tall buildings and communication towers (Audubon 1967 [1840], Buckley 2

1998, Avery et al. 2002, Evans and Sordahl 2008). Vultures are drawn to these structures not only because of the perches provided, but because of the obstruction currents that are created when a strong wind hits a vertical surface, like a building, creating an updraft (Cone 1962), which vultures use for energy-efficient flight. Another manner in which vultures have taken advantage of human-altered landscapes is through the exploitation of road-killed animals as a food source. Vultures are able to take advantage of the food source, and spend less time searching for food (Kelly et al. 2007).

As both human and vulture populations continue to grow, negative interactions between humans and vultures have become more common. For example, vultures are susceptible to high levels of heavy metals; such as lead (Carpenter et al. 2003), stationary and moving object collisions (Sprunt 1937, Blackwell and Wright 2006, De Lucas et al. 2008), habitat loss (Jackson

1983), and other anthropogenic disturbances. Globally, there is an increasing frequency of human-vulture conflicts that have risen with urban and rural land development.

The increase of Black and Turkey vultures throughout the United States has also impacted humans and their property. Vultures have been estimated to cause over a million dollars in property damage to residential, commercial, industrial, and agricultural areas in Florida between 1993-2001 (USDA 2005).These problems include, but are not limited to the (1) tearing of plastic, rubber, and leather coverings of personal property (USDA 2003); (2) destruction and removal of insulation and linings on personal and commercial property such as vehicles and buildings (USDA 2010); (3) scratching of paint on vehicles (USDA 2010); (4) tearing of roof shingles on buildings (USDA 2003); (5) reported damage to landscaped plants due to excessive roosting numbers and fecal matter (USDA 2003); (6) power outages associated with the accumulation of fecal matter on electric transmission towers; and (7) loss or injury of livestock 3 in Florida and elsewhere (USDA 2005). Many communities in the United States encourage the removal of vultures due to real or perceived property and agricultural damage.

To address adverse human-vulture interactions, several approaches have been taken in the management of vultures. Among these are: deployment of vulture carcasses, taxidermic effigies, or decoy effigies (Avery et al. 2002, Tillman et al. 2002); relocation of problem individuals

(Humphrey et al. 2000); broadcasting of noise deterrents (Schlierf et al. 2007); as well as lethal measures (Runge et al. 2009). While such management techniques may be – or may seem to be individually – effective in certain situations, they may not work at every site that has a vulture problem. For example, the deployment of vulture carcasses is not always an effective long-term solution (Sordahl 2013). Humans with a perceived vulture problem become frustrated when these techniques do not work, which has led to use of lethal measures to remove vultures

(Virginia Department of Game and Inland Fisheries 2013).

As vulture and human populations increase, the need for more frequent and more intensive control efforts could negatively impact North American vultures. There is an evident need for evaluation of the efficacy and impacts of current efforts, development of sound management guidelines, and education on the role of vultures in ecosystems, their ecological needs, and the nature and context of the behavior that sometimes is found problematic for humans (Appendix A). Many of the conflicts and management techniques that arise from human- vulture interactions in the Americas may not only inform management efforts for problem species elsewhere, but also provide insight useful in the conservation of threatened vulture species.

The occurrence of a problematic vulture roost at the Guadalupe Center of Immokalee, an early childhood education center in southwest Florida, was the focal point for a conflict between 4 humans and vultures. The Center had up to 250-300 Black and Turkey vultures on their property on a daily basis throughout most of the year (pers. comm.). Vultures were observed perching on the Center building and surrounding structures, as well as using an associated retention pond for bathing and drinking; and adjacent mowed areas for social interactions.

My primary objective in this study was to evaluate and determine site-specific solutions to a problematic vulture roost location problem. In order to provide site-specific solutions to vulture roost problems, an understanding of vulture behavior and roost habitats used by vultures was essential to determine why the Guadalupe Center and areas surrounding it were attractive as a roost site. A secondary objective included the evaluation of management techniques that were not site-specific. Of the techniques implemented, those techniques that were site-specific were expected to be more effective in discouraging and altering the birds’ use of the property than those techniques that were not site-specific.

MATERIALS AND METHODS

Study area

Fieldwork was conducted at the non-profit Guadalupe Center of Immokalee, an early childhood education center that served as a year-round roost site for up to 250-300 Black and

Turkey vultures. The Guadalupe Center is located at the southern edge of Immokalee (ca. 24,000 population), Collier County, Florida (26°25′16″N, 81°25′22″W) (Figure 1). Agricultural fields, as well as some natural landscapes, dominate the area surrounding Immokalee.

Figure adapted Figure adapted

(

2009)

Tampa, Tampa,

Star shows location of Guadalupe Center roost. Center location Guadalupe of shows Star

Florida Center for Instructional Technology, University of South Florida, Technology,South Instructional Florida, University Center of Florida for 1: Map of study area in Collier County, Florida. County, in ofMap Collier 1: study area

from the Figure

The Center is surrounded by southern slash pine (Pinus elliottii var. densa) flatwoods with a saw palmetto (Serenoa repens) understory and scattered cabbage palms (Sabal palmetto) to the north, east, and west. This area also fringes an extensive bottomland hardwood, wetland drainage composed primarily of baldcypress (Taxodium distichum), red maple (Acer rubrum), and Brazilian pepper (Schinus terebinthifolius) (Figure 2). This natural area is privately owned and part of the Big Cypress Basin managed by the South Florida Water Management District.

Earth image taken on 22 December 2010) 22 Earth image taken December on

(Google

(shaded in yellow) in (shaded

east, and west of the Center consists of a pine flatwoods ecosystem that fringes an extensive an that extensive of fringes flatwoods ecosystem ofa Center consists west pine the east, and

2: The Guadalupe Center of Immokalee is located south of Immokalee and is part of a small subdivision, Collier Collier south a of of and small subdivision, Immokalee is part ofImmokalee is located The 2: Center Guadalupe

Figure Village.The area north, bottomland wetland hardwood, drainage 9

A drainage canal runs east-west along the north side of the Guadalupe Center property

(Figure 3), which carries runoff from the parking lot of an apartment building approximately 300 meters to the west of the Guadalupe Center. Prevailing west winds are funneled down the canal and hit the west facing wall of the west-most building of the Guadalupe Center. This wall has no roof overhang, resulting in an upward obstruction current that creates an updraft “elevator” for the vultures to use. Directly to the west of the Center is a 0.6-hectare retention pond with low sloping sides allowing vultures to access water for drinking and bathing. To the west and south of the Center are an isolated subdivision, Collier Village, and another retention pond. The city landfill is located approximately 1.5 kilometers southeast of the Guadalupe Center. Throughout the city, many dumpsters, including some at the Center and others at businesses nearby, provide vultures with access to reliable and predictable food sources.

Earth image taken on 22 December Earth2010) December on 22 image taken

TM 300+ Black and Turkey vultures. (Google vultures. Turkey 300+ and Black

3: Aerial photograph of the Guadalupe Center in Immokalee, Florida. The Guadalupe Center was used as a as roost used Center was Guadalupe Florida. Immokalee,The in the Aerial Center of Guadalupe photograph 3:

Figure location for 250 11

The Guadalupe Center property has many features that make it attractive to the vultures.

These features include the architecture of the Center building, chain-link fences surrounding the

Center’s property, eleven light poles located in the parking lot, an air-conditioning unit and enclosure, open mowed areas, a retention pond, a water pump, and irrigation sprinklers. All of these features together resulted in the attractiveness of the Guadalupe Center property as a roost site. Many of the features provided perch sites for the vultures to engage in social behaviors, or provided the birds with water for drinking and bathing.

Roost habitat characteristics

Data on habitat characteristics of the Guadalupe Center roost were collected prior to the initiation of management techniques in order to compare the Center’s roost to other vulture roosts in the United States. Habitat characteristic data were collected in order to determine why certain areas attract more vultures, and if management techniques could be developed to discourage the vultures from occupying urban roost areas. The Guadalupe Center vulture roost was compared to 26 vulture roosts in the United States. Comparative data were obtained by personal observation, as well as personal observations and data published by others.

Habitat data that were collected included:

1. Presence of structures, both natural and anthropogenic, that allowed for the creation of

obstruction currents and thermals: Structures promoting the creation of obstruction

currents included large vertical surfaces, such as a cliffs or buildings. Structures

promoting the creation of thermals included areas with an increased albedo, often devoid

of vegetation such as agricultural fields or large areas of pavement. 12

2. Availability of food: Due to the presence of roadways and trash receptacles throughout the

United States, all vulture roosts analyzed were assumed to be near food due to the

proximity of roadways to all roosts observed.

3. Availability of water: Any mention of water near the roosts, whether natural or anthropogenic

were considered to be used by the vultures.

4. Area type: The type of area was categorized as urban, rural, or natural. Urban areas were

considered to be regions with anthropogenic buildings or other structures used by the

vultures for roosting. Rural areas were considered to be regions with agricultural fields,

equipment, and buildings. Natural areas were those areas where anthropogenic buildings

were not present or used by the vultures when roosting.

5. Roost tree type: If vultures roosted in trees, the type of trees was recorded. In some cases,

vultures only roosted on anthropogenic structures, thus no roost tree type was recorded.

6. Species composition of the roost: Data were collected on species of birds at each roost to act

as a comparison to the Guadalupe Center roost. Species composition was categorized as

only Turkey Vulture, only Black Vulture or Black and Turkey vulture.

Some roost descriptions did not mentioned any of the above characteristics; these were categorized as “information not available or N/A” and were not included in the analysis of those characteristics.

Pre-observational control data collection

Preliminary observational control data were collected from 7-11 March 2011 using 10 x

35 binoculars. Observations were made during all daylight hours, to understand the daily use of the area by the vultures. The age (immature or adult), species (Black Vulture or Turkey Vulture), 13 behavior, and location of the vultures were recorded hourly to gain an understanding of what aspects of the Guadalupe Center were attractive to the birds.

Vultures were classified as either immature or adult. Since transition to complete adult plumage is gradual, hatching-year and second-year birds were categorized as immature and all after-second-year birds as adults (Pyle et al. 2008). Immature Turkey Vultures were identified by their gray head and/or dark bill tip (Kirk and Mossman 1998, Pyle et al. 2008). Adult Turkey

Vultures were identified by their red head and lighter bill tip (Kirk and Mossman 1998).

Immature Black Vultures were identified by their darker and less wrinkled head, in addition to the conspicuous presence of feathers on the crown and nape of the head (Buckley 1999, Pyle et al. 2008). Adult Black Vultures were identified by their dark, very rugose, featherless appearing head (Buckley 1999).

Pre-observational behavioral sampling observations were made using instantaneous-scan sampling (Altmann 1974). The behavior of each individual vulture was recorded. This resulted in

32 vulture behavior counts during which 9 specific behaviors were identified for observation during post-management efforts (Davis 1983a, b).

The behaviors of the vultures were initially classified using nine categories (Figure 4).

Because of functional relatedness and sample sizes, for data analysis the following behaviors were reorganized: (a) spread-wing and delta-wing postures were grouped together into one category referred to as sunning behavior, and (b) drinking and bathing were grouped together into one category as water-related behaviors that occurred at the pond and at pools created by the sprinklers or rain.

A. Inactivity: Vultures engaged in standing, B. Spread-wing: Vultures with wings lying, or general perch behavior. There was fully extended and exposed to the sun. no movement or interaction with other individuals.

C. Delta-wing: Vultures with wings partially D. Preening: Vultures preening feathers extended inward toward the body and facing anywhere on their own body. the sun.

E. Allopreening: Vultures preening the F. Agonistic: Vultures engaged in feathers anywhere on the body of another aggressive behavior with other individual. individuals. This behavior included activities such as chasing or pecking another vulture. Agonistic interactions require and were recorded as two or more individuals. Per Hinde (1970) agonistic behavior was described collectively as attacking, fleeing, or submissive behaviors. 15

G. Fidgeting: Vultures using bills to peck or H. Drinking and bathing: Vultures pick with no apparent “goal-directed” intent drinking water in pond, canal, or from at nearby items. Vultures were seen pecking temporary pools created by rain or the at roof shingles, insulation, and other Center sprinkler system Vultures anthropogenic items at the roost site. bathing and dipping either their wings and/or head into water.

Figure 4: Types of vulture behavior observed at the Center (Davis 1983a, b).

Management techniques

Management techniques were implemented in the areas on the property where the vultures caused the most problems (Appendix B). Management techniques were implemented gradually as permitted in order to see how each alteration of the property affected the vultures’ location and behavior.

Vulture management efforts were categorized for data analysis as follows due to the simultaneous implementation of some techniques: (1) pre-management, management prior to my involvement; (2) pond-area management, management at the pond, mowed areas, fences and water pump; (3) roof-area management, management on the roof and light poles; (4) management disruption, management efforts employed, but no longer effective or intact; and (5)

Center-initiated management, non-site-specific management implemented and suggested by others (i.e. pinwheels and vulture carcasses).

Vulture management categories were a posteriori defined categories based on the chronological implementation of management by the Center. Categories were organized because 16 of the sequential and simultaneous implementation of the management techniques at the Center

(Appendix C). For example, management at the pond, mowed areas, fences and water pump were included in one category (pond-area management) because of the simultaneous implementation of those techniques. The chronological implementation of management at the

Center is as follows: pre-management, pond-area management, roof-area management, management disruption, and Center-initiated management.

Management techniques included:

Pond-area management

1. Fences. The first management technique implemented was the placement of a thin wire

above the fence stretched between every other fence pole, approximately 6 meters apart.

The wire was stretched 10-15 centimeters above the fence, but vultures were able to push

the wire down and still perch. The wire was moved 20 centimeters above the fence, and

vultures were still able to stretch out the wire and perch. Since the wire was not effective,

two monofilament lines (0.75 mm diameter, 50 lb. fish line) were stretched 20-25

centimeters above the fence (Figure 5). The line needed to be tight in order to prevent

vultures from pushing it down allowing them to still perch as noted with the lower quality

wire. The monofilament line was stretched between each fence pole at 3 meters rather

than 6 meters to prevent vultures from pushing the line down. Lines were placed less than

20-25 centimeters above the fence to prevent vultures from perching underneath.

A sprinkler system was installed on the north fence, but the system was defective

and created excess water for the vultures to use for drinking and bathing. At times the

sprinkler was functioning during both pre- and post-management of the property.

Figure 5: Two strands of monofilament line were installed 20-25 centimeters above chain- link fences on the Guadalupe Center’s property to discourage vulture perching.

2. Pond. The installation of silt fencing around the pond perimeter was used to discourage

vultures from the property (Figure 6). The silt fencing was one meter tall and made of

heavy plastic. Wooden stakes were pre-installed on the fence and were set at 3 meter

intervals. The fencing was installed at the water’s edge, but was not moved as water

levels increased and decreased.

Figure 6: Silt fencing was installed around the Center pond to prevent vultures from using the water for bathing and drinking.

3. Water pump. A PVC pipe extending to the pond was installed to eliminate water access

to the birds (Figure 7).

Figure 7: PVC pipe was extended from the water pump to prevent vultures from using the water.

4. Mowed areas. When the grass in the area was not mowed, allowing the grass to grow

tall, vultures were deterred from occupying the region. When the area was mowed,

monofilament was stretched in a zigzag pattern across the area to prevent the vultures

from landing in the region (Figure 8). The poles were approximately 6-12 meters apart

and the line stretched approximately 9 meters from pole to pole.

Figure 8: Monofilament line stretched across the mowed area of the Center property.

Roof-area management

1. Building architecture. Bird spikes (Bird B Gone Stainless Steel 5.0” width and 4.75”

height) were placed along the peaks and edges of the roofs and awnings on the west-end

to prevent perching (Figure 9A and 9B). Two motion-activated sprinklers were installed

on the roof as well to further deter the vultures from perching (Figure 9C).

A. B.

Figure 9: Management of the Center roof and awning. A. Bird spikes placed on roof. B. Bird spikes placed on awning. C. Motion-activated sprinkler installed on roof.

2. Light poles. Polycarbonate plastic bird spikes (Bird-B-Gone polycarbonate plastic 3”

width) were installed on the light shields to prevent vultures from perching on these

structures; vultures were still able to perch atop the supporting light poles (Figure 10).

Figure 10: Bird spikes placed on the light shields of the light posts at the Center.

Center-initiated management

1. Pinwheels. The Center installed pinwheels on the north fence, mowed areas, and roof.

The pinwheels were installed arbitrarily throughout the mentioned areas.

2. Vulture carcasses. The Center hung three Black Vulture carcasses in the trees separating

the pond from the northern mowed area. The three carcasses were hung upside down in

three adjacent trees.

Post-management data collection

During and after the implementation of management techniques, the age, species, behavior, and location of the vultures on the Center property were recorded daily from April

2011 – December 2012 for a total of 85 days.

Without individually-marked birds, I could not determine the frequency with which individuals were observed. However, the number of vultures present varied from day to day and

Turkey and Black vultures are known to use multiple roosts such that the roost composition was likely fluid (Rabenold 1983). Consequently I viewed the outcomes of the management of the roost each day as independent events.

Data analysis

Each daily sample point was treated as a separate data point. For those days when more than one count was recorded, the first sampling of the day was used. The first sampling was used because the behavior of the vultures was most likely not altered by my presence during the first count. Data from the wet season (May-October) were not included in statistical analyses because the vultures on the property dramatically decreased each wet season without regard to management as communicated by the Center. 24

To examine the overall effect of management techniques on the population of vultures at the Guadalupe Center roost, a one-way permutation test was used with a Monte Carlo Simulation of the p-value (B = 9,999). Total Black Vulture, adult Black Vulture, and immature Black

Vulture average population numbers were analyzed and compared during pre- and post- management efforts.

A one-way permutation was used with a Monte Carlo Simulation of the p-value (B =

9,999) to test the effectiveness of each categorical management technique (pre, pond-area, roof- area, management disruption, and Center-initiated). Average Black Vulture population numbers were analyzed during each of the management technique categories.

To examine the dispersion of the vultures on the property during the different categories of management (e.g. pre, pond-area, roof-area, management disruption, and Center-initiated), a

Pearson’s chi-squared test was used. The five categories were compared to each proceeding management technique category (i.e. pre vs. pond-area, pond-area vs. roof-area, roof-area vs. management disruption, and management disruption vs. Center-initiated) to determine if there was a change in the dispersion of the vultures across the property.

To examine the difference in vulture behavior during each management category, a one- way permutation test was used with a Monte Carlo Simulation of the p-value (B = 9,999). The proportion of vultures engaged in each of the seven behavioral categories during each management effort were calculated for data analysis. A one-way permutation test was used with a Monte Carol Simulation of the p-vaule (B = 9,999) to compare overall pre- and post- management behavioral differences.

All statistical tests were conducted using R (R Core Team 2013) using the package coin

(Hothorn et al. 2006). Significance was accepted at an α-level of 0.05. 25

RESULTS

Roost habitat characteristics

Data were gathered from 27 vulture roosts in the United States (Table 1). Comparative data were obtained by personal observation, as well as personal observations and data published by others. Of the 27 roosts analyzed, over 70% had both Black and Turkey vultures present in the roost. All other roosts had only one species present, either the Black Vulture or Turkey

Vulture.

Over 70% of the roosts analyzed were associated with the formation of obstruction currents similarly to the Guadalupe Center roost. Of vulture roosts analyzed including the

Guadalupe Center roost, all were associated with thermals or structures located nearby that would create thermals, except one where there was no mention of either.

Roosts located near a source of water accounted for 89% of the roosts analyzed. All 15 roosts located in Florida, were located near water or were associated with water. Food was found to be available near all vulture roosts due in part to the amount of roadways located throughout the country.

The roosts analyzed were composed of a variety of species of roost trees. Of the roosts observed, only 11% did not describe or include either conifers or snags, suggesting a strong preference for those roost tree types. In the morning and evening at the Guadalupe Center roost, vultures perched within the forested area on exposed horizontal branches of slash pines and snags and on the top of cabbage palms.

Anthropogenic structures were located near almost every roost; only 22% of the roosts did not directly mention anthropogenic structures in their descriptions.

yes

N/A

WATER

yes

FOOD

yes

N/A

THERMALS

yes

N/A

N/A*

CURRENTS

OBSTRUCTION OBSTRUCTION

both

SPECIES

Black Vulture Black

Turkey Vulture Turkey

rural

urban

AREA

natural natural

ROOST LOCATION ROOST

Table 1: Habitat characteristics and composition of 27 vulture roosts found in the United States the United and in 27 composition found roosts of Table vulture characteristics 1: Habitat

*N/A data not available available data not *N/A

Radford Army Ammunition Plant, Montgomery County, Virginia County, Montgomery Plant, Ammunition Army Radford

Dutch Gap Conservation Area, Chesterfield County, Virginia County, Area, Chesterfield Conservation Gap Dutch

Leesburg, Loudoun County, Virginia County, Loudoun Leesburg,

Nacogdoches County, Texas County, Nacogdoches

Holston River Ammunition Plant, Hawkins County, Tennessee County, Hawkins Plant, Ammunition River Holston

Gettsyburg National Military Park-Quarry, Adams County, Pennsylvania County, Adams Park-Quarry, Military National Gettsyburg

Gettsyburg National Military Park-Harpers Hill, Adams County, Pennsylvania County, Adams Park-Harpers Hill, Military National Gettsyburg

Gettsyburg National Military Park-Big Round Top, Adams County, Pennsylvania County, Adams Top, Round Park-Big Military National Gettsyburg

Malheur National Wildlife Refuge, Harney County, Oregon County, Harney Refuge, Wildlife National Malheur

Chatham County, North Carolina North County, Chatham

Coralville Dam, Johnson County, Iowa County, Johnson Dam, Coralville

Decorah, Winneshiek County, Iowa County, Winneshiek Decorah,

Everglades National Park, Miami-Dade County, Florida County, Miami-Dade Park, National Everglades

Peace River, DeSoto County, Florida County, PeaceDeSoto River,

Myakka River State Park, Manatee County, Florida Florida State ManateePark, County, River Myakka

Lake Butler, Baker County, Florida Baker County, Lake Butler,

Okeechobee County, Florida County, Okeechobee

Bull Pond, Putnam County, Florida County, Putnam Pond, Bull

Lakes Park, Lee County, Florida Lakes LeePark, County,

North Fort Myers, Lee County, Florida Lee County, Myers, Fort North

Orange County Sewage Treatment Plant, Orange County, Florida County, Orange Plant, Sewage Treatment County Orange

Orlando Wilderness Park, Orange County, Florida County, Orange Park, Wilderness Orlando

Bonnet Creek, Osceola County, Florida County, Osceola Creek, Bonnet

Disney World, Osceola County, Florida County, Osceola World, Disney

Harns Marsh, Lee County, Florida Lee HarnsCounty, Marsh, Babcock Ranch, Charlotte County, Florida County, Charlotte Ranch, Babcock Guadalupe Center, Collier County, Florida County, Collier Center, Guadalupe

SOURCE

Prather 1976 et al.

Duerr Duerr 2009

Nickens 2008 Nickens

Haskins 1972 Haskins

Tanner 1947 and Stewart 1983 and 1947 Tanner

Wright 1984 Wright

Davis 1979 Davis

Rabenold 1987 Rabenold

personal observation personal

personal communication personal

personal observation personal

Tillman et al. 2002 et al. Tillman

personal observation personal

Stolen 1996 Stolen

Stolen and Taylor 2003 Taylor and Stolen

personal observation personal

no no

yes

STRUCTURES

ANTHROPOGENIC

ROOST TREE ROOST

sycamore and pine and sycamore

N/A

pine

sycamore and beech and sycamore

pine

pine and hardwoods and pine

pine

cottonwood

deciduous and mixed conifers mixed and deciduous

N/A

deciduous trees snags and deciduous

cabbage palm and snags and palm cabbage

cabbage palm and live oak snags oak live and palm cabbage

cabbage palm, live oak snag, and baldcypress and snag, oak live palm, cabbage

pine

cabbage palm snags and oaks lacking foliage lacking oaks and snags palm cabbage

bay, pine and baldcypress and pine bay,

baldcypress and snags and baldcypress

pine

baldcypress

cabbage palm snags palm cabbage

baldcypress and snag pines snag and baldcypress

pine

pine, cabbage palm, and snags and palm, cabbage pine,

ROOST LOCATION ROOST

Table 1 (continued): Habitat characteristics and composition of 27 vulture roosts found in the United States United in and found composition roosts ofthe Tablevulture (continued): characteristics 1 27 Habitat

Radford Army Ammunition Plant, Montgomery County, Virginia County, Montgomery Plant, Ammunition Army Radford

Dutch Gap Conservation Area, Chesterfield County, Virginia County, Area, Chesterfield Conservation Gap Dutch

Leesburg, Loudoun County, Virginia County, Loudoun Leesburg,

Nacogdoches County, Texas County, Nacogdoches

Holston River Ammunition Plant, Hawkins County, Tennessee County, Hawkins Plant, Ammunition River Holston

Gettsyburg National Military Park-Quarry, Adams County, Pennsylvania County, Adams Park-Quarry, Military National Gettsyburg

Gettsyburg National Military Park-Harpers Hill, Adams County, Pennsylvania County, Adams Park-Harpers Hill, Military National Gettsyburg

Gettsyburg National Military Park-Big Round Top, Adams County, Pennsylvania County, Adams Top, Round Park-Big Military National Gettsyburg

Malheur National Wildlife Refuge, Harney County, Oregon County, Harney Refuge, Wildlife National Malheur

Chatham County, North Carolina North County, Chatham

Coralville Dam, Johnson County, Iowa County, Johnson Dam, Coralville

Decorah, Winneshiek County, Iowa County, Winneshiek Decorah,

Everglades National Park, Miami-Dade County, Florida County, Miami-Dade Park, National Everglades

Peace River, DeSoto County, Florida County, PeaceDeSoto River,

Myakka River State Park, Manatee County, Florida Florida State ManateePark, County, River Myakka

Lake Butler, Baker County, Florida Baker County, Lake Butler,

Okeechobee County, Florida County, Okeechobee

Bull Pond, Putnam County, Florida County, Putnam Pond, Bull

Lakes Park, Lee County, Florida Lakes LeePark, County,

North Fort Myers, Lee County, Florida Lee County, Myers, Fort North

Orange County Sewage Treatment Plant, Orange County, Florida County, Orange Plant, Sewage Treatment County Orange

Orlando Wilderness Park, Orange County, Florida County, Orange Park, Wilderness Orlando

Bonnet Creek, Osceola County, Florida County, Osceola Creek, Bonnet

Disney World, Osceola County, Florida County, Osceola World, Disney

Guadalupe Center roost composition

The total number of Black and Turkey vultures at the Guadalupe Center changed throughout the year and roughly matched a change in the wet and dry season (Figure 11).

Black Vultures far out-numbered Turkey Vultures at the site in 17 out of 22 months of observation during both pre- and post-management efforts (Figure 11). Since Turkey Vultures were not present in as high of numbers as Black Vultures, were often only located in the forested area north of the Center, and were only present early in the morning before leaving the roost and at dusk when coming to roost, their data were excluded from further analysis.

Figure 11: Total number of Black and Turkey vultures present at the Guadalupe Center from March 2011 through December 2012.

The average numbers of immature and adult Black Vultures were recorded at the

Guadalupe Center roost. Prior to management, there were more immature Black Vultures on property than during management (Figure 12). After management, there were comparatively more adult Black Vulture at the roost than immature Black Vultures (Figure 12).

Figure 12: Average number of immature Black Vultures and adult Black Vultures during pre- and post-management (during the dry season at the Guadalupe Center).

Management techniques

The average number of Black Vultures on the property significantly decreased when comparing pre- to post-management efforts (Figure 13: Z = 3.63, p < 0.01). Similarly, the average number of adult Black Vulture significantly decreased when comparing pre- and post- management efforts (Figure 14: Z = 2.2192, p = 0.017) as well as the average number of immature Black Vultures (Figure 15: Z = 4.1, p < 0.001).

The average number of Black Vultures on the property decreased significantly when comparing pre-management efforts to pond-area management efforts (Figure 16: Z=2.4673, p<0.01). The average number of Black Vultures did decrease when comparing pond-area management to roof-area management, but it was only marginally significant (Figure 17:

Z=1.9047, p=0.05). When comparing the roof-area management to when management was disrupted there was a marginally significant increase in the average number of Black Vultures on property (Figure 18: Z=1.7166, p=0.05). When comparing Center-initiated management to management disruption, there was not a significant decrease in the average number of Black

Vultures on the property (Figure 19: Z=1.4871, p=0.162).

The areas the vultures occupied during pre-management and during pond-area management differed significantly (Figure 20 A, B: X2=65.89, p<0.001). During pre- management the vultures were found primarily at the pond (Figure 20 A, B). Prior to pond-area management, vultures were on the fences 30% of the time (Figure 20 A, B). After pond-area management only 15% of vultures were found on the fences (Figure 20 A, B). After pond-area management was implemented, the vultures were also observed more than expected on the building and at the pond. In addition, there was a significant difference between the areas occupied by the vultures when comparing pond-area management to roof-area management 31

(Figure 20 C, D: X2=251.69, p<0.001). After roof-area management, vultures occupied the forested area north of the Center more often than expected and were observed on the building and at the pond less than expected.

Vultures used different areas at the Center when roof-area management was compared to days during management disruption. During management disruption, vultures returned to the building, fences, and pond (Figure 20 E, F: X2=86.46, p<0.001). Vultures were not observed as often in the forested area north of the Center during days when management was disrupted.

When comparing the days during management disruption to Center-initiated management there was no significant difference in the areas the vultures used on the property (Figure 20 G, H:

X2=5.42, p=0.144), suggesting that management disruption and Center-initiated management did not alter the dispersion of the birds on the property.

Figure 13: Average number of Black Vultures during pre- and post- management at the Guadalupe Center. The top and bottom of each box indicate the 75th and the 25th percentiles. The line through the box is the median, and the error bars are the 5th and 95th percentiles.

Figure 14: Average number of adult Black Vultures during pre- and post-management at the Guadalupe Center. The top and bottom of each box indicate the 75th and the 25th percentiles. The line through the box is the median, and the error bars are the 5th and 95th percentiles.

Figure 15: Average number of immature Black Vultures during pre- and post-management at the Guadalupe Center. The top and bottom of each box indicate the 75th and the 25th percentiles. The line through the box is the median, and the error bars are the 5th and 95th percentiles.

Figure 16: Average number of Black Vultures during pre- and pond- area management at the Guadalupe Center. The top and bottom of each box indicate the 75th and the 25th percentiles. The line through the box is the median, and the error bars are the 5th and 95th percentiles.

Figure 17: Average number of Black Vultures during pond-area and roof-area management at the Guadalupe Center. The top and bottom of each box indicate the 75th and the 25th percentiles. The line through the box is the median, and the error bars are the 5th and 95th percentiles.

Figure 18: Average number of Black Vultures during roof-area management and management disruption at the Guadalupe Center. The top and bottom of each box indicate the 75th and the 25th percentiles. The line through the box is the median, and the error bars are the 5th and 95th percentiles.

Figure 19: Average number of Black Vultures during management disruption and Center- initiated management at the Guadalupe Center. The top and bottom of each box indicate the 75th and the 25th percentiles. The line through the box is the median, and the error bars are the 5th and 95th percentiles.

Figure 20: Dispersion of Black Vultures on the Guadalupe Center property during pre- and pond-area management. A. Total number of Black Vultures on areas of property. B. Percentage of Black Vultures on areas of property.

Figure 20 (continued): Dispersion of Black Vultures on the Guadalupe Center property during pond-area and roof-area management. C. Total number of Black Vultures on areas of property. D. Percentage of Black Vultures on areas of property.

Figure 20 (continued): Dispersion of Black Vultures on the Guadalupe Center property during roof-area and management disruption. E. Total number of Black Vultures on areas of property. F. Percentage of Black Vultures on areas of property.

Figure 20 (continued): Dispersion of Black Vultures on the Guadalupe Center property during management disruption and Center-initiated management. G. Total number of Black Vultures on areas of property. H. Percentage of Black Vultures on areas of property.

Behavior

Vultures were engaged in similarly proportioned behaviors during all management categories (Figure 21). Vultures engaged in behaviors described as inactive, the majority of the time on the property. The second most common behavior was preening in all management efforts. Sunning and water-related behaviors were exhibited more often than agonistic, allopreening, and fidgeting.

The differences between pre- and post-management proportions were tested for each of the seven behavior categories. There was a significance difference between most pre- and post- management behaviors when analyzing each behavior separately against management type.

When comparing water-related (Z=-5.001, p<0.001), sunning (Z=-4.918, p<0.001), inactive (Z=-

5.5549, p<0.001), allopreening (Z=-2.9609, p=0.007) and preening (Z=-6.7252, p<0.001) during pre- and post-management, all behaviors significantly decreased between pre- and post- management. Fidgeting (Z=-2.5276, p=0.014) and agonistic (Z=-2.1475, p=0.0305) behaviors were significantly different between pre- and post-management as well.

A. B.

D. C.

Figure 21: Proportion of vultures engaged in each of seven behaviors observed at the Guadalupe Center roost during each management category.

DISCUSSION

Guadalupe Center vulture roost composition

The composition of the population of vultures at the Center was important in management efforts. There were two species present on the property; Black Vultures and Turkey

Vultures. Black Vultures far outnumbered the Turkey Vultures and were present throughout the day and in all areas of the property. Turkey Vultures, on the other hand, were often present only early in the morning before leaving the roost or late at night when coming to roost. Turkey

Vultures were observed most often in the forested area north of the Center and not on the Center property, thus they were not part of the main roost problem at the Guadalupe Center. In addition

Black Vultures are most commonly associated with vulture roost damage of the two species of vultures.

The age composition of the roost was important to management as well. Of the Black

Vultures present at the Guadalupe Center roost, the majority were immature birds. Rabenold

(1987) found that immature Black Vultures were site faithful, as opposed to adults that did not stay at the same roost consistently. Similarly, Stewart (1978) found that Black Vulture roosts consisted largely of young nonbreeding aged birds. The birds at the Guadalupe Center most likely consisted of nonbreeding birds either too old or too young to breed suggesting that the birds would stay in the area as long as the benefits of the site outweighed the costs.

Vulture response to management efforts

The total number of Black Vultures at the Guadalupe Center decreased significantly between pre- and post-management efforts suggesting that the management techniques implemented discouraged vulture use of the Center’s property. The implementation of 46 management techniques also caused the vultures to alter their use of the property after each management effort category.

During pre-management, vultures were found across all areas of the property. Areas of the property that the vultures used included the building, fences, pond (including the surrounding mowed area), and the forested area north of the Center. After pond-area management, vultures were observed more often than expected on the buildings and at the pond. The birds, however, were observed less than expected on the fences and in the forested area. Overall, the number of vultures decreased, but a higher proportion of birds did occur at the pond. The birds may have occurred at the pond more often due to the scarcity of the resource and difficulty in accessing the resource. The vultures’ persistence of staying in areas near the water suggests that the water and surrounding areas were the major draw of the property. It is also important to note that the silt fence surrounding the pond often fell down, thus was never fully implemented allowing vultures access to water.

Roof-area management followed the management conducted at the pond-area. The birds used the property differently when comparing pond-area and roof-area management. Vultures were observed more than expected in the forested area north of the Center and less than expected in all other areas of the property during roof-area management. The movement of the birds to the forested area suggests that the roof-area management was successful in deterring the majority of the birds from the Center’s property. The combined management efforts at the pond and roof cut off the vultures’ access to water, perch sites, and areas for social and maintenance behaviors.

Many of the management techniques deteriorated after their initial implementation (i.e. management of the pond, mowed areas, fences, and building all fell into disrepair). The silt fencing was under water, monofilament lines on the fences and in the mowed area were broken, 47 and the sprinklers and bird spikes on the roof were not functioning. During times of management disruption, the birds were observed throughout all areas of the property. The birds were also observed less often than expected in the forested area north of the Center’s property. This suggested that the intact management did encourage the birds to use areas other than the Center’s property.

After management disruption, the Center implemented a few techniques suggested by other individuals. The techniques suggested by others were not designed for the specific population of vultures occupying the Guadalupe Center property and were not designed for the problems associated with the Guadalupe Center property. These techniques included the hanging of vulture carcasses near the pond and the placement of pinwheels in the mowed areas, roofs, and fences. There was no significant difference in the birds’ use of the property during the non-site- specific Center-initiated management and management disruption. This suggests that our management which was site-specific and problem-specific was more successful than the Center- initiated management, which was not site-specific.

Use of noise, visual, and chemical repellants in vulture management

The Center often initiated management techniques that were not site-specific and were suggested by other individuals. These non-site-specific management techniques were not based on the behavior of the vultures or the habitats used by the vultures at the Guadalupe Center.

These techniques were suggested by individuals and agencies that had implemented these techniques successfully at other vulture roosts or with other bird species, but had not visited the

Guadalupe Center site specifically. The non-site-specific management techniques failed to take into account the population of vultures or the physical features of the Center. It seemed clear from my observations that as long as the benefits for the vultures at the roost site outweigh the 48 energy costs required to continue to use the site, the vultures would continue to occupy the

Center grounds. The use of noise repellants, such as shouting and creating loud sounds, fireworks and other pyrotechnics; visual repellants, such as pinwheels, dead vultures, and owl decoys; and chemical repellants only garnered short-term successes. Birds, including vultures, readily habituate to stimuli that cause no harm. The attraction of the site remained with the use of noise, visual, and chemical repellants and the vultures continued to return until the site was altered to make it less attractive.

Use of noise repellants. Prior to my involvement at the Center, personnel attempted to deter the vultures with a variety of noise repellants. Center personnel used firecrackers to discourage vulture use of the Center. The vultures left the property only momentarily after the use of pyrotechnics. The Center staff would also yell and clap their hands at the vultures, but the vultures would only fly to another area of the property. The vultures habituated to the loud noises produced by the Center staff, thus noise repellants did not deter the vultures from the property.

Use of visual repellants. Pinwheels, toys incorporating a folded plastic rosette attached by a pin or nail to a stick so that the vanes of the rosette catch the wind and cause it to spin, were suggested and installed by Center personnel in hopes of dispersing vultures. Center personnel installed the pinwheels on 22 March 2012, and the vultures continued to use the site, but ignored areas where the pinwheels were installed. A week after the installation of the pinwheels the vultures began to perch immediately next to them.

Other visual deterrents, such as owl decoys were used prior to my visit to the site. Center personnel noted that the owl decoys did not work. Similarly, I observed Black Vultures at the

Seminole Casino of Immokalee perched right next to an owl decoy intended to scare the vultures.

Clearly any deterrent value of owl decoy was short-lived. 49

A common vulture management technique employed across the United States is the use of vulture effigies or carcasses in efforts to disperse roosts. Center personnel obtained a permit from the United States Fish and Wildlife Service for the allowable take of Black Vultures.

Against recommendations, three Black Vultures were shot on Center property on 31 March

2012. The dead vultures were hung upside down by their feet in trees adjacent to the north side of the pond, where most vultures were located. This was in accordance with instructions provided by the U.S. Department of Agriculture (Seamans 2004, Humphrey et al. 2010, [and others]). I visited the property later that evening and viewed vultures in the forested area north of the Center and on light poles. Vultures continued to increase in numbers over the next few weeks as the dead vultures decomposed. Often, USDA staff members recommend obtaining permits for the allowable take of vultures after all other management resources have been exhausted (USDA

2003). The allowable take of vultures is becoming more common in vulture management across the country as USDA officials promote the use of vulture effigies and carcasses as successful roost dispersal mechanisms. The few studies that have examined the long-term effectiveness of vulture effigies and carcasses as roost dispersers have been inconclusive and most studies have been conducted at communication tower roosts (Avery et al. 2002).

The effectiveness of vulture effigies after the initial displacement of a vulture roost has not been studied adequately. In June 2012, a Turkey Vulture carcass was hung from one of two communication towers at a vulture roost in northeast Iowa. The carcass provided by the USDA, initially displaced the vultures from both communication towers and even led them to abandon their roost a ½ kilometer away (Sordahl 2013). The vultures had occupied the roost area for over

20 years. In September 2012, approximately 30 vultures returned to use the roost, but it is assumed these vultures were northern migrants that used the roost as a stopover site while 50 migrating south (Sordahl 2013). The resident Turkey Vultures would typically have departed from the roost in October to migrate south. The vultures did return in March 2013. Currently, there are 50-100 vultures using both communication towers and the night roost. The vultures are not occurring in as high of number as the past (as many as 300), but they have returned, suggesting that effigies and carcasses are not a long-term permanent solution to dispersing roosts.

Researchers do not fully understand why vultures will abandon a roost site permanently or temporarily when a carcass or effigy is hung. The public and researchers often anthropomorphize vultures and attribute roost dispersal to the fact that vultures do not want to be near other dead vultures. At the Guadalupe Center, vultures at times were found dead and on occasion other vultures were seen eating the vulture carcasses (pers. obs.). Vultures are known scavengers and will scavenge their own species if the opportunity arises (Audubon 1967 [1840], personal observations). My study shows similar ineffectiveness of this management technique; the use of vulture effigies and carcasses has limited short-term effectiveness as a deterrent strategy of vulture roosts.

Use of chemical repellants. The vulture roost at the Guadalupe Center was a human-interest story that was told through radio, television, and newspapers. Responses and suggestions from the public for dispersing the vultures were numerous. One individual offered to spray a homemade concoction that was said to be effective in deterring birds from properties. The individual would not disclose what ingredients were in the mixture, but said it would be effective against the vultures. The product was sprayed in an area where the vultures were roosting on a fence. While the vultures did leave the immediate area while the individual was spraying, they returned within 30 minutes after the spraying was completed. The spray had no visible lasting 51 influence on the vultures, but did kill some of the vegetation in the area where it was sprayed.

Other studies support the ineffectiveness of chemical repellants in dispersing vulture roosts

(Schlierf et al. 2007).

Role of roost habitat characteristics in vulture management

After gaining an understanding of the problems and areas used by the birds, I looked at other roosts in the United States to understand what habitat characteristics were shared between the Guadalupe Center roost and other roosts.

A comparison of the vulture roost at the Guadalupe Center to other roosts in the United

States was important to determine what habitat characteristics were typically associated with large roosts. Understanding what habitat characteristics are attractive for a communal roost will allow researchers and wildlife management personnel to better assist individuals with roost problems on their property.

Most of the vulture roosts I surveyed were associated with habitat parameters that promote the production of air currents, such as obstruction currents and thermals, for energy efficient flight in vultures. Before the arrival of Europeans to North America, the eastern United

States was predominately covered by forests, which were heat absorbing. This feature limited the ability of vultures to use the pre-European forests of eastern North America. Today, much of the

United States is covered by agricultural fields and cities, which reflect large amounts of heat

(Jackson 1991). Roads, large concrete lots, water surfaces, and even buildings may enhance the production of thermals (Geiger 1965). The reflection of heat creates thermals, which create eased flight for soaring birds, such as vultures.

The unevenness of the land surface and borders between forests and clearings promote the development of obstruction currents. Large vertical surfaces, like the Guadalupe Center 52 building contribute to the formation of obstruction currents as well. Studies show that areas that promote obstruction currents and thermals, allowing for effortless flight, are preferred sites for vulture roosts (Thompson et al. 1990).

Data on roost tree type were collected because some trees have been reported to be more attractive to birds as they create more accessible perch sites than others (Wright et al. 1986,

Thompson 1987). Of the roosts analyzed in this study, conifers and snags were consistently used as preferred roost trees. Vulture roost habitat studies found similar results. Thompson found in his study that taller trees and conifers were preferred to smaller deciduous trees (1987). At the

Guadalupe Center, the roost trees most commonly occupied were conifers or snags. There are several reasons why large birds, like vultures prefer to roost in conifers. Tall trees, like conifers have branches that are well-spaced which allow for a vulture’s large wingspan and easy takeoff

(Thompson 1987). Conifers tend to have larger diameter branches that move less in the wind, providing a steady perch for vultures (Koford 1953). Conifers also have a horizontal arrangement of branches that allow for easy flight takeoff (Wright et al. 1986). Similar to conifers, snags, trees without an increased amount of foliage were found to be preferred by vultures due to eased flight (Ceballos and Donazar 1990).

The preference of vultures to conifers and snags at roosting sites has been well- researched, but the preference to have a roost located by a water source has not been discussed as thoroughly. Similar to the Guadalupe Center roost, Stolen (1996) found that vultures in Florida prefer tall trees that are near water. In addition, Audubon in his accounts of the Black Vulture and Turkey Vulture described both birds as preferring roost areas near water (1967 [1840]).

Other species of vultures, like the California Condor, are known to roost near water sources as 53 well (Snyder and Snyder 2000). There seems to be a preference in areas with characteristic dry seasons, for vulture roosts to be located near a source of water.

At the Guadalupe Center, there was a large open mowed area that vultures frequented. In one study, researchers found that areas of open ground near a roost were used between one to three hours before leaving to roost (Rabenold 1987). In addition, Audubon described a roost of over a thousand Black Vultures along a river with the ground beneath the roost devoid of vegetation (1967 [1840]). Vultures at both the Guadalupe Center and in other studies used the open ground for social interactions and maintenance behaviors. At the Guadalupe Center, monofilament line was stretched across mowed areas to discourage vulture use in those regions.

Management techniques should be implemented in open areas of vulture roosts to prevent vultures from engaging in daily social and maintenance behaviors.

An understanding of vulture roost habitat characteristics is important not only for management, but for conservation. Many species of Old World vultures are either listed as threatened or endangered (IUCN 2012) and researchers have found that Old World vultures share similar roost site characteristics (Yamac 2006). The roost sites studied by Yamac showed a strong preference to areas that promoted the creation of obstruction currents and a preference of conifers as roost trees (2006). Old World vultures are at risk for extinction, thus any information about the preferred habitat characteristics for roosting in New World vultures has the potential to assist with the conservation efforts of the Old World species.

Importance of vulture behavior in management plans

The majority of birds observed at the site were engaged in maintenance behaviors

(preening) or behaviors described as inactive (lying or perching) during all management efforts.

Other individuals have found similar results at roosts throughout the United States. Stolen (1996) 54 found that Black Vultures at a roost in central Florida spent most of their time engaged in maintenance behaviors such as, preening and scratching; and social behaviors, such as agonistic interactions and allopreening (1996). In addition, Clark and Ohmart (1985) found that Turkey

Vultures spent the majority of their time engaged in preening and resting behaviors. Davis

(1983b) also found that over 50% of Turkey Vultures engaged in preening behavior pre- and post-roosting. Similarly behavioral patterns have been observed in other New World vultures.

For example, Koford (1953) found that preening was the most common behavior exhibited by

California Condors at roosts.

An understanding of what the vultures are doing at a particular site and how the birds use the site are important in effective vulture management. This information will help determine what management techniques should be implemented to deter vulture use of the property.

Vultures at the roost were often observed drinking or bathing at the pond and preening in the mowed area after using the water. Many of the birds at the Guadalupe Center engaged in preening were wet suggesting the importance of the water to the roost location. While the vultures did engage in behaviors the same proportionate amount of time during pre- and post- management efforts, the total population was significantly reduced after management techniques were initiated. The understanding of the birds’ behavior at the roost site allowed me to suggest management techniques based on their location and overall behavior at the site.

Vulture social and maintenance behaviors at the Guadalupe Center did not change overall between pre- and post-management strategies. When analyzing each behavior separately, the behaviors most common were found to be the most significantly different between pre- and post- management. This is mostly likely caused by the reduction in vulture numbers between pre- and post-management. Vultures seemed to exhibit the same proportionate amount of behavior 55 regardless of management efforts. This suggests that management does not affect these behaviors negatively. Vultures were still able to engage in maintenance behaviors, behaviors essential for survival, regardless of management efforts.

While the social and maintenance behaviors of the birds did not change, how the birds used the property changed dramatically depending on the management strategy. Vultures were present throughout all areas of the property when management was not intact and not site- specific. When the pond-area and roof-area management were intact vultures used the areas of the property differently. In addition, management strategies at the pond and roof areas affected the birds by dramatically reducing the number of vultures on the property.

Community activities contributing to vulture roost problems

While the Center may be able to alter and manage their property to make it less attractive to the vultures, they will be unable to alter the community’s actions that contribute to the large population of vultures in the area. The community of Immokalee is partially accountable for the vulture roost problem at the Guadalupe Center. In Collier County, there are over 100,000 acres of farmland and in 2007 over 175,000 acres of vegetables were produced (USDA 2009). Large numbers of Black Vultures and a few Turkey Vultures have been observed feeding on rotting vegetables in the agricultural fields that surround Immokalee (Jerry Jackson, pers. comm.). Black

Vultures are known to take advantage of vegetative matter as a food source. Black Vultures in

Louisiana were reported to have eaten sweet potatoes when traditional food sources were scarce

(McIlhenny 1945). In addition, Haverschmidt (1947) reported that Black Vultures would occasionally eat the African oil palm fruits that fell to the ground and would eat coconut flesh left over at factories in Coronie. In Immokalee, culled vegetables are left to rot in large piles, which were a predictable food source for many birds in the area, including vultures. 56

There may be some form of seasonality to the presence of vegetable cull piles. I visited two cull pile sites from April 2011-December 2012. Culled vegetables were not present or very limited between June-October 2011 and June-October 2012. The vultures at the Guadalupe

Center were not present in high numbers during the characteristic wet season months, but these months also coincide with the lack of culled vegetable piles in the area. The agricultural practices of Immokalee may contribute to the vulture problem at the Guadalupe Center.

The availability of culled vegetables is not the only food source that vultures may depend on in the area. Dumpsters and garbage litter the streets of Immokalee, often trash receptacles are left open for vultures to take advantage of and have contributed to the large vulture population in the area. The Seminole Casino of Immokalee is located less than one kilometer from the

Guadalupe Center and has a large dumpster that is regularly left uncovered. I visited the dumpsters 56 times between April 2011 and December 2012 and viewed over 1,000 Black

Vultures, with a maximum of 72 Black Vultures observed on one occasion. There are countless dumpsters located throughout Immokalee and very rarely are the dumpsters covered properly.

While vultures at the Guadalupe Center roost can be encouraged to leave the site, vultures will continue to exist in high numbers in the community due to human activities.

Changing agricultural practices (the elimination of large rotting vegetable piles), encouraging an anti-litter behavior (closing trash receptacles and trash clean-up), and the removal of road-killed animals found within city limits would help reduce local vulture populations. A typical vulture diet consists primarily of carrion which is unpredictable and unevenly distributed, thus the predictability of food (i.e. trash receptacles or culled vegetable piles) in the city must be addressed. 57

Vandalism of management methods at the Guadalupe Center was an issue as well.

Individuals would often break into the Center’s property to use the pond for fishing. The individuals would knock down the silt fencing that surrounded the pond. The silt fencing was installed to prevent vultures from gaining access to the water and vultures were able to access the pond after vandalism. In addition to the vandalism, individuals that broke into the Center property would also leave litter and fish remains around the pond, providing the vultures with more foraging opportunities. Community awareness of the vulture problems within the city limits should be addressed. The Guadalupe Center could have signs attached to their fences explaining the management and importance of keeping the vultures off of the property.

What made the Guadalupe Center attractive as a roost site?

The vultures’ use of the Guadalupe Center as a roost site was not due to one singular reason or feature of the property. The Guadalupe Center provided the vultures with all the necessary needs for a relatively easy and comfortable existence, including food, water, perch sites, areas for social interactions, and proximity to nesting and roosting areas. All of the features together and their interconnectedness provided the ideal roost site for the vultures. If all of these features had not been present together the vultures may not have occurred in such high numbers on the property.

The property across from the Center had a few characteristics similar to that of the

Guadalupe Center property, but no vultures. One feature shared between the Guadalupe Center and the nearby property was the presence of chain-link fences. The chain-link fences differed from the Center’s in that the chain-links projected above the fences’ top support (Figure 22).

Vultures could not easily perch on these fences as compared to the Center’s fence. 58

Another feature shared between the Center and the other property was the presence of a retention pond surrounded by trees. The retention pond at the other property had much steeper slopes than the pond at the Guadalupe Center. The Guadalupe Center pond had shallow areas that provided easier access for bathing and drinking for the vultures.

While the two properties shared the presence of fences for perching and a retention pond that provided the birds with water, it did not have the combination of features that the Guadalupe

Center property had. The Center property provided the birds with not only perch sites and water, but also food (dumpsters), areas for socialization (large mowed areas and roost tree habitat), proximity to ideal nest habitat and roost trees (forested area north of the Center), and areas that promoted the creation of thermals and obstructions currents (building architecture).

Figure 22: Fence located across from the Guadalupe Center property that possibly discouraged vultures from using it as a perch site.

Need for effective vulture management

Vultures have long been living in close association with humans, taking advantage of their middens and waste. Human-vulture conflicts have been documented in as early as the 1800s

(Audubon 1967 [1840]). Audubon (1967 [1840]) described both Turkey and Black vultures as being “half domesticated” in cities, taking advantage of human food scraps. In his account of the

Black Vulture, he described early vulture management of roofs and chimney tops. Individuals would place spikes and pieces of glass on roofs and chimneys tops to prevent the roosting of vultures in the southern United States (Audubon 1967 [1840]).

The need for information and research regarding Black and Turkey vulture roosts in association with humans is recognized (Bruggers et al. 2002), but there have been few long-term studies on vulture management. The importance of developing an understanding of vulture roost management is crucial to continue on a path of positive coexistence between humans and vultures.

If vulture management methods that result in positive outcomes for both humans and vultures are not reached, lethal forms of management may be employed. Because of the ecosystem services that Black and Turkey vultures provide and because they are long-lived species (Clapp et al. 1982) with low reproductive rates, laying only two eggs per nesting season

(Jackson 1983, Stewart 1983), the use of lethal means to control them may have significant negative consequences for the species.

Lethal management techniques have not been proven successful in dispersing vulture roosts. In the Dutch Gap area of Chesterfield, Virginia, Black Vultures were routinely killed from 2002-2006. Over 1,200 Black Vultures were killed, but vultures still continued to cause significant property damage to the area (Virginia Department of Game and Inland Fisheries 60

2013). As of 2007, there were over 400 Black Vultures and approximately 30-40 Turkey

Vultures occupying the area. The local culling of vultures was ineffective at reducing the amount of property damage caused by vultures due to the immigration of new vultures into the area.

Long-term studies on vulture demographics are needed to understand the effect of lethal methods in vulture management. The lack of data on vulture demographics and the compliance with state and federal regulations protecting these native birds have created difficulties (Runge et al. 2009) and should discourage individuals from including lethal measures in their management plans.

The ability to effectively manage a large vulture roost will unquestionably lead to fewer human-vulture conflicts. Less human-vulture conflicts will ensure not only the safety of vulture populations, but result in less property and agricultural damage. Any knowledge as to why vultures are attracted to certain areas will benefit not only the Guadalupe Center site, but other areas that are experiencing similar vulture-related problems. Finding an economical and effective way to deter the vultures from agricultural and personal property is essential for vulture populations to continue to thrive.

The various management techniques employed at the Guadalupe Center roost site dramatically reduced the number of vultures present on the property and affected their overall use of the site. Persistence and consistency are keys to successful management of vulture roost problems. Management should be site-specific and gradual. The roost at the Guadalupe Center had several areas that were attractive to the birds, and each area needed to be addressed individually to discourage vulture use of the property. Every area that was attractive to the vultures required a different management method. While there are instances where each technique of managing vultures has proven successful, none provide a conclusive solution for all vulture management problems. Understanding site-specific and problem-specific parameters is 61 essential to developing effective management for vultures. In most cases, vulture roost problems will need to be solved using a variety of techniques (Appendix D). 62

APPENDIX A

Black and Turkey vulture species information

Current and historical range. The family Cathartidae includes all extant species of New World vultures. There are three species of New World vultures that occur within the United States;

Turkey Vulture (Cathartes aura), Black Vulture (Coragyps atratus), and the California Condor

(Gymnogyps californianus). Two of the species, the Black and Turkey vulture occur throughout the state of Florida. Both Black and Turkey vultures act as frequent avian scavengers in the southeastern United States, where they share similar habitats and food resources (Coleman and

Fraser 1987).

While both Black and Turkey vultures only occur in the New World today, fossil records show that cathartids did exist in Europe from the early Eocene (Feduccia 1996) to the early

Miocene (Rich 1983). The earliest fossil records show that cathartids occurred during the early

Oligocene in the New World (Feduccia 1996), and fossils of both Black and Turkey vultures have been found in lower Pleistocene deposits in Florida (Wetmore 1956). Based on fossil records, both species of vultures have had extensive opportunities for interaction and coexistence in the state of Florida.

Black Vultures are a resident species throughout much of their range, including Florida

(Buckley 1999). The Black Vulture range extends north to Pennsylvania, encompasses the southeastern United States and extends south through South America (Buckley 1999). Within the last seventy years, the Black Vulture range has shifted, moving farther north through the United

States (Greider and Wagner 1960). While Black Vulture populations have been increasing in the

United States since 1966 (Sauer et al. 1997), their populations are still at risk due to human 63 activities including trapping, shooting, poisoning, pesticide contamination, loss of habitat, and frequent disturbance of nest and roost sites (Buckley 1999).

Turkey Vultures differ from Black Vultures as they are a highly migratory species.

Populations in south Florida are augmented by migrating birds as early as October through the end of winter (Stevenson 1970). The Turkey Vulture range extends north into southern Canada and extends south through southern South America (Kirk and Mossman 1998). During the winter months, Turkey Vultures migrate to the southern parts of their range which include the southeastern United States, western California, the eastern Caribbean islands, Mexico, Central

America, and South America (Kirk and Mossman 1998). Turkey Vulture populations are increasing, along with their breeding range extending farther north (Mossman 1991), but they face similar population risks as Black Vultures.

Ecosystem services. Black and Turkey vultures play an essential ecological role in the environment. They are the only living obligate terrestrial vertebrate scavengers (Houston 1979,

Ruxton and Houston 2004). Vultures are key scavengers, signaling (by their presence) to other terrestrial vertebrate scavengers, where animal carcasses are located (Houston 1979).

Because vultures act as the “garbage disposals” of our ecosystems, they and other scavengers are fundamental to terrestrial ecological communities. While performing ecosystem service, vultures, other vertebrate scavengers, insects, other invertebrates and fungi assist in nutrient cycling by quickly disposing of decaying carcasses and thus reduce the potential spread of disease (Markandya et al. 2008).

A vulture’s ability to dispose of diseased carcasses is an ecosystem service that is essential for the health of humans and other animals worldwide. Bacteria associated with diseases such as anthrax (Darling and Bates 1912) and botulism (Kalmbach 1939) are destroyed 64 in the digestive tracts of vultures. If vultures were not present, these carcasses would decompose slowly, thus facilitating the spread of these pathogens. Most wild animals do not die because of predator-prey interactions, but from such things as disease, parasites, starvation, and a variety of other non-predatory related causes (Houston 1979).

The measurement of metals in feathers may allow birds to act as bioindicators for the health of many different ecosystems (Burger 1993). The position of vultures at the top of the food chain and their ability to bioaccumulate heavy metals allow vultures to act as biological indicators of pollutants in the environment (van Wyk et al. 2001).

Foraging and diet. Vultures feed on a wide variety of both domestic and wild carrion (Coleman and Fraser 1987), and exploit the high numbers of road-killed animals found throughout the

United States (Sprunt 1937, Thiel 1976, Stewart 1978). Vultures typically prefer to feed on fresh carrion (Rapp 1943, Houston 1986); however they cannot always do so because of the toughness of the skin; therefore they either wait for a carcass to decompose further, or wait for the assistance of other carrion feeders (Wallace and Temple 1987).

Black and Turkey vultures share similar food resources, but their food-finding abilities differ greatly. Turkey Vultures differ from Black Vultures in that they use their highly developed olfactory organs to find their food primarily by smell (Bang 1964, Stager 1964). Turkey Vultures prefer to feed on smaller food items, are less likely to feed near humans, and are more often to feed in smaller groups or alone (Kirk and Mossman 1998). They are less aggressive than Black

Vultures and are often outcompeted at food sources (Kirk and Mossman 1998).

The Black Vulture diet is highly variable when compared to the Turkey Vulture; it includes carrion, vegetative matter (McIlhenny 1945, Buckley 1996), and even in extreme cases live prey (Sprunt 1946, Lovell 1947, Jackson et al. 1978). Black Vultures rely heavily on sight as 65 well as on Turkey Vultures to find carrion (Buckley 1996, 1997). The ability of the Turkey

Vulture to use its heightened sense of smell often involves Black Vultures following them to carcasses (Buckley 1996). Turkey Vultures typically fly at lower heights where their olfactory senses are the strongest and Black Vultures soar much higher looking for Turkey Vultures on or near a carcass (Buckley 1996).

A dominance hierarchy exists between and within species of vultures at carcasses

(Wallace and Temple 1987). Turkey Vultures almost always arrive at a carcass first because of their superb sense of smell (Kirk and Houston 1995). Black Vultures are far more aggressive than Turkey Vultures and will often displace Turkey Vultures from a carcass (Stewart 1978,

Wallace and Temple 1987, Buckley 1997). While a large group of Black Vultures may displace a single Turkey Vulture, a solitary Black Vulture will have a more difficult time getting rid of a

Turkey Vulture (Wallace and Temple 1987, Houston 1988, Buckley 1996). Because large groups of Black Vultures can easily displace Turkey Vultures (Stolen 1996) Turkey Vultures will typically feed on smaller carcasses (Stewart 1978). Feeding vultures will seldom tolerate more than one vulture at a carcass (Prior and Weatherhead 1991). Typically one vulture will feed while other vultures wait close by (Kirk 1988).

For vultures that scavenge in groups, the potential advantages presumably outweigh the costs. There are definite disadvantages to feeding in a large group such as the obtainment of less food for individuals (Lindström and Ranta 1993). There are also advantages of foraging in large groups such as increased alertness for predators (Clark and Mangel 1986) and the possible assistance in opening a carcass (Wallace and Temple 1987).

Communal roosting. Black and Turkey vultures both roost communally and will often do so together; communal roosts are important to many species of birds, not only vultures during at 66 least part of their annual cycle (Beauchamp 1999). The communal roost is a significant aspect in the social behaviors of vultures. Communal roosts may be permanent (roosts used yearly), seasonal (roosts formed during breeding season), or temporary based on location to food sources or migration (Sweeney and Fraser 1986). Black Vultures may use the same communal roost site for decades (Prather et al. 1976). The number of individuals in Black Vulture roosts varies and may even contain up to thousands (Prather et al. 1976). Turkey Vultures often will roost with

Black Vultures at a communal roost site increasing the number of individuals. Turkey Vultures will form single species roosts of up to 300 individuals (Kirk and Mossman 1998).

While it is known that vultures and other birds communally roost, there are several hypotheses as to why birds choose to roost communally. Potential advantages of communal roosting include, but are not limited to: thermoregulatory benefits (Brenner 1965), reduced predation risks (Lack 1968), transfer of information regarding foraging (Ward and Zahavi 1973), reduced travel distances between daily activity centers (Caccamise and Morrison 1986), and the dispersion of foragers to reduce intraspecific competition (Chapman et al. 1989). Communal roosts act as a gathering place for both adult and juvenile vultures (Buckley 1999). There are disadvantages of communal roosting as well. There may be increased competition for food

(Alexander 1974), mates (Hoodgland and Sherman 1976) and preferred roost sites (Swingland

1977). Vultures use roosts to communicate and socialize. Vultures do not have a syrinx or voice box so gathering in large groups is essential for communication.

Breeding and nesting. Black and Turkey vultures do not build nests. They lay their eggs, usually two, on the ground, in abandoned buildings, caves, or hollow trees (Jackson 1983). Black and Turkey vultures differ somewhat in nesting locations because Turkey Vultures are solitary nesters and Black Vultures are known to nest in close proximity to others (Jackson 1983). 67

Black Vultures maintain long-term pair bonds and are monogamous (Decker et al. 1993).

They will reproduce annually (Rabenold 1983) once sexual maturity has been reached. Prior to nesting, Black Vultures will perch together near the nest site before the nesting begins (Jackson

1983). Black Vultures may begin nesting as early as February and as late as May. The peak of egg-laying occurs from late February to the end of April (Buckley 1999). Black Vulture pairs may continue to use the same site for nesting for years if breeding is successful (Rabenold 1983).

In Florida, both parents will incubate the eggs for a period of 28-30 days and young will fledge the nest at approximately 98 days (Jackson 1983). The birds may have young on the nest as early as late March and as late as early August (Buckley 1999). The peak months for young on the nest are from early April until early July (Buckley 1999). Young are long-term dependents on their parents (Jackson 1975) and also may associate at communal roosts and while foraging after fledging (Rabenold 1986).

Turkey Vultures are most likely monogamous and will mate for life (Buckley 1999).

Turkey Vultures differ from Black Vultures in breeding season. Turkey Vultures will lay eggs from mid-April until early July with the peak season occurring from the end of April to the end of May (Kirk and Mossman 1998). Turkey Vultures may have young on the nest from late May to mid-September with the peak season occurring from late May to mid-August (Kirk and

Mossman 1998). Turkey Vulture incubation periods are long and similar to those of the Black

Vulture. Turkey Vultures most likely breed annually, similar to Black Vultures, once sexual maturity is reached (Jackson 1983). There is probably a long-term dependency of young to the parents, comparable to the Black Vulture (Jackson 1983).

Habitat use. The habitat of the Black and Turkey vulture differs based on use. The nesting habitat of both vultures should include forested areas or partially forested areas with nest sites, 68 such as hollow trees, abandoned buildings, or other dark recesses (Kirk and Mossman 1998).

Undisturbed sites are preferable since human disturbance can reduce breeding success (Jackson

1983).

The preferred roosting habitat of vultures should include areas with large trees (Davis

1983b) and areas that promote the creation of thermals and updrafts for flight (Thompson et al.

1990). Typically, roosts will be found near some source of water (Prather et al. 1976).

Throughout the United States vultures have been known to roost on anthropogenic structures, such as communication towers (Evans and Sordahl 2009) and buildings (Audubon 1967 [1840]).

Foraging habitat should include open areas, such as fields or pastures where food can be easily found visually for Black Vultures or by scent for Turkey Vultures (Kirk and Mossman

1998, Buckley 1999). The preferred habitat of both vultures should be a mixture of open areas for foraging; areas that include remote nest sites, such as dense thick woodlands, hollow trees, or abandoned buildings; and large stands of tall trees for roosting (Kirk and Mossman 1998,

Buckley 1999).

APPENDIX B

Problems associated with vulture use of the Guadalupe Center property

The main difficulty associated with the Guadalupe Center roost was finding a way to stop the vultures from creating the problems they were causing on the property. Ultimately and optimally this required encouraging the birds to abandon the roost.

To effectively manage the problems, all areas that the vultures occupied on a daily basis needed to be addressed.

The problems associated with the vultures on the property included:

1. Fences. The chain-link fences that surrounded the Center’s property provided the vultures

with access to abundant perch sites.

2. Drainage canal. A drainage canal ran parallel to the fence immediately adjacent to the north

side of the Guadalupe Center’s property and the forested wetland (Figure 3). The canal

ran east-west, creating an almost effortless flight path for the vultures due to the

channeling of the prevailing winds. The vultures on occasion used the canal for bathing

and drinking. The canal also provided a food source for the vultures when it dried

seasonally; invertebrates and fish that lived in the canal were isolated in smaller pools

and were easily caught or died as the pools dried.

3. Pond. A pond located immediately to the west of the Center building was used by the vultures

for drinking and bathing. Vultures were present in lower numbers during the wet season

suggesting that the pond may be the reason the vultures were on the property.

4. Building architecture. The architecture of the Center building encouraged the perching of

vultures on the roof and surrounding structures. The Center roof generated thermals that

facilitated nearly effortless flying for the vultures. Vultures damaged the roof by tearing 70

shingles with their bills and through the high levels of excrement deposits on the

building. There were five skylights located at the peak of the Center’s main roof. The

vultures perched on the skylights resulting in excrement accumulation and scratching of

the plastic.

At the west end of the building, where most the birds congregated, the vultures

took advantage of an obstruction current (Figure 23). The eaves of the building did not

overhang which encouraged the formation of obstruction currents; wind hitting a vertical

object and shunting upwards. Without the overhanging eave the wind was shunted

vertically, creating an “elevator” for the birds, allowing for flight with minimal energy

expenditure.

Figure 23: Black Vulture using obstruction current created by the architecture of the building.

There were definite patterns to where the vultures perched on the buildings based on the location of whitewash from fecal matter (Figure 24A). Vultures typically perched along the edges or peaks of the buildings and awnings (Figure 24B). The peak of the buildings facilitated easy takeoff for the birds. Birds perched there could take advantage of wind from any direction. Some of the roofs at the Center had lightning rods at the peak (Figure 24). Vultures were unable to perch on the apex of roofs with lightning rods suggesting that bird spikes could prevent vultures from perching on other Center roofs.

The nature of the Center’s roofs contributed to the vulture problem as well. The rough asphalt shingles that covered all of the rooftops provided the vultures with a surface that promoted traction and allowed for ease of movement on the roof as well as a firmer footing for takeoff and landing. The steepness of some of the roofs (8/12 pitch;

34o) (Figure 24A) also discouraged perching. The Center’s main roof was low sloping

(3/12 pitch; 14o) allowing the vultures access to abundant perch sites (Figure 7).

A. B.

Figure 24: A. Vultures preferred to roost at the peaks and edges of roofs as can be seen by the pattern of excrement. B. Vultures were able to take off more easily from the edges and peaks of the roof. The lightning rods prevented the vultures from perching on top of the roofs.

5. Light poles. Eleven light poles located to the south of the Center building in the parking lot

were used by the vultures for perching. The light poles and light shields were covered in

fecal matter due to the consistent perching of the vultures (Figure 25). Of the 11 light

poles in the Guadalupe Center parking lot, only the four most westerly poles were used

by the vultures. These poles were the nearest to the obstruction current created by the

building architecture and closest to the retention pond.

Figure 25: Vultures used the Center’s light poles and light shields for perching.

6. Air-conditioning units. An air-conditioning unit and enclosure located immediately to the

west of the Center building was used as a perch site for the vultures (Figure 26A). A low

concrete wall that surrounded the air-conditioning unit attracted the vultures for

additional perch sites and was covered in fecal matter. Vultures destroyed pipe insulation

and feathers were drawn into the air-conditioning unit filters (Figure 26B).

A. B.

Figure 26: A. Vulture perching on air-conditioning unit and enclosure. B. Damage caused by vultures ripping apart the installation around the air-conditioning unit pipes.

7. Mowed areas. Vultures were consistently present and engaged in maintenance and social

behaviors in a mowed area located directly north of the pond (Figure 27).

Figure 27: Vultures used a mowed area north of the pond for social and maintenance behaviors.

8. Forested area. A forested area located north of the Center was an attractive roost site for the

vultures. The vultures used the snags (standing dead trees), pines, and cabbage palms for

perch sites. The cabbage palms that the vultures used for roosting had tops that had been

flattened by the roosting of the vultures, thus further increasing their suitability as vulture

perch sites. The area was immediately adjacent to, but not located on the Guadalupe

Center property. 76

9. Water pump. A water pump located east of the pond and west of the Center building was

used to maintain the water levels of the retention pond. Water levels were maintained to

avoid thermal stratification and minimize algal blooms and the resuspension of

previously deposited materials. Water spewing from the pump provided an additional

water source for the vultures (Figure 28).

Figure 28: Water from the water pump allowed vultures to have additional access to a water source.

10. Irrigation sprinklers. The presence of irrigation sprinklers on the Center property provided

the vultures with additional water sources. Sprinklers would often run all day and create

streams and puddles for the vultures to bathe in and drink from (Figure 29).

Figure 29: Vultures using a puddle created by excessive irrigation of the lawns at the Guadalupe Center.

APPENDIX C

Ineffectiveness and limitations in the implementation of management techniques at the

Guadalupe Center roost site

The immediacy of the vulture roost problem at the Guadalupe Center resulted in part to the ineffectiveness of some of the management techniques. To generate true experimental data, the roost should have been observed for longer than one week prior to the start of management in order to collect more baseline data. Data on behavior and precipitation (and other abiotic factors) was limited due to the immediacy of the vulture roost problem. Abiotic data was not included in the study due to the lack of preliminary data and due to simultaneous management efforts.

The implementation of some of the techniques by Center personnel did not allow for the collection of precise experimental data during management. Several suggestions were provided to the Center personnel on how to adequately manage for vultures in each area of the Center’s property. Occasionally, management techniques were not conducted as instructed or conducted simultaneously with other management techniques, at times resulting in the prevention of true experimental data.

Center employees would also sometimes use management techniques that were not suggested in hopes of deterring the vultures more quickly, in those cases I incorporated responses of the vultures to their management efforts into data collection efforts to document the possible impact of those management techniques.

The limitations and effectiveness of the vulture management techniques as employed are discussed below.

1. Fence management. Vulture fecal matter can be highly corrosive (Figure 26), therefore the

prevention of vultures from perching on the fences was critical. The vultures were 79 attracted to the fences because there were abundant perches that provided them with an area to rest, socialize, preen, sun and easily takeoff.

Prior to my involvement at the Center, motion-activated sprinklers were installed on the fences. The sprinklers did work to deter vultures from perching, but often broke down. If sprinklers were not maintained, vultures would readily habituate when the sprinklers no longer emitted water and the birds would continue to use fences as perch sites.

Prior to the installation of the monofilament, a thin wire was stretched above the fences (Figure 30A). Vultures were able to stretch the wire and enable perching. Due to the ineffectiveness of the wire, the Center installed a monofilament line above the fence to prevent birds from perching on the fences (Figure 30B). The monofilament line broke easily and was not resistant to the excessive heat associated with Florida’s subtropical climate.

The placement of the monofilament above the fences was somewhat ineffective in preventing vultures from perching as well. Vultures were sometimes able to push the monofilament up and perch beneath it.

A. B.

Figure 30: A. Damage caused by vultures excessively perching and defecating on the Center’s fences. B. Vultures were able to push down and stretch a thin wire.

2. Pond management. The management of the pond was important in making the site less

attractive to the vultures. After the initial installation of the fencing around the north side

of the pond, most birds congregated away from the pond or on the south side that had

open water suggesting that silt fencing would adequately prevent vultures from using the

pond.

After the initial installation, silt-fencing was installed around the entire perimeter

of the pond to prevent vultures from using the water. The fence was not placed directly at

the waterline to prevent vultures from using the water. Pond levels would increase and

decrease during the wet and dry season, thus the fence needed to be moved. Silt-fencing

was often underwater or would have dry areas exposed allowing vultures access to the

water.

3. Roof management. The architecture of the Guadalupe Center encouraged the high number of

vultures roosting on the property. The birds were concentrated on the west end of the

Center’s main building where the presence of a vertical updraft occurred. The eaves on 81

the Center building did not overhang promoting the creation of the obstruction current. If

the eaves did overhang, the upward flowing air would hit the eave and be pushed outward

horizontally, resulting in little vertical airflow.

The prevention of the vultures from easily using the obstruction current created on

property was important. Bird spikes were installed along the edges and ridges of the main

roof. The bird spikes were not adhered properly to the roof and often detached from the

shingles and were not replaced.

In addition to the bird spikes, two motion-activated sprinklers were installed on

the Center roof due to the ineffectiveness of the bird spikes. The sprinklers on the

Center’s roof were battery operated and would often break down allowing the vultures to

habituate to non-working sprinklers.

4. Light pole management. Vultures used light shields and light poles for perching on the

Center’s property. The bird spikes attached to the top of light shields prevented vultures

from perching on the shields, although vultures were still able to perch on top of the pole.

Overall, bird spikes were effective in deterring the vultures from perching at the specific

site where the spikes were affixed.

5. Air-conditioning unit management. It was important to discourage vultures from using the

concrete wall that surrounded the air-conditioning units as a perch site. Black Vultures

are known to peck and rip apart rubbers seals, leather boat cushions, and other similar

structures. At the Guadalupe Center, Black Vultures ripped apart and destroyed foil

wrapped insulation around pipes leading to the air-conditioning unit. The vultures were

likely attracted to the foil insulation because they often will rip apart foil wrappers found

in dumpsters and along roads and find food inside. They were attracted to the vibrations 82

of the pipes as well as they are similar to the vibrations produced by dying animals. After

the installation of the monofilament line on the fences, most vultures stopped perching on

the enclosure around the air-conditioning units, but no direct management was

implemented to the enclosure or unit.

6. Management of mowed area. The monofilament line that was stretched across the mowed

area north of the Center did prevent the high numbers of vultures from using the area.

Often lines were found broken and were never replaced, allowing the vultures to continue

to use the area.

7. Management of forested area north of Center property. The Center did not own the

forested area north of their buildings, thus no direct management could be implemented.

8. Water pump management. The Center personnel extended the pipe from the water pump to

the pond to prevent the vultures from using the pump as an additional water source. The

pipe was never fully extended to the water line, thus vultures were able to still access the

water to some extent. It was critical to prevent vulture access to water on the Center

property.

9. Irrigation sprinkler management. The regular irrigation system at the Center sometimes

provided a water source for the vultures. The Center was advised to stop the use of the

sprinklers during the day or to run the sprinklers less often to discourage vulture use.

When irrigation sprinklers were allowed to run continuously for long periods of time,

vultures were present in high numbers. They bathed in the “shower” provided by

sprinklers and in puddles created by the sprinklers.

APPENDIX D

Future management suggestions for the Guadalupe Center roost site and other problematic vulture roosts

A variety of management techniques to discourage vulture use of the property were suggested to the Guadalupe Center. In some cases the Center was unable or did not follow through with management suggestions. These suggestions are listed below and may be considered in future management efforts.

1. Fence management. The thin wire and monofilament line installed at the Center were not

adequate in preventing vulture use of the fences. Future management should include a

wire that can withstand a variety of environmental conditions and is not susceptible to

stretching in lieu of monofilament line. Additional lines of wire may be needed to further

prevent vulture perching. Two wires should be installed above the fence, one on either

side, in order to prevent the birds from pushing the line to one side and perching.

Staggering the two lines may be beneficial to prevent even further perching underneath

the line.

If the installation of wire is not possible, the planting of vegetation along fences

may prevent the vultures from using the fences. A fence located north of the Center

building had a hedge that grew above the fence line; vultures did not use this fence for

perching. The Center and other individuals that own fences that are susceptible to

perching vultures, could plant hedges adjacent to fences to prevent vulture perching.

The location of fences is important in vulture management as well. The fence

located north of the Center’s playground was not used by the vultures. The vultures most

likely did not make use of this fence due to the shade from nearby trees, distance to water 84

source, and the bend in the canal that prevented wind-tunneling from creating an

effortless flight path for the vultures.

2. Pond management. If the installation of fencing around a water source is not an option

individuals could encourage the growth of tall vegetation along the water’s edge. On the

northwest side of the Center’s pond there was a heavy concentration of cattails. Vultures

were never observed inside or in front of the cattails suggesting that the vegetation acted

as a natural barrier between the vultures and the water source.

Vultures also frequented the areas around the pond that were shaded by trees. To

discourage further use, trees could be pruned to allow more sunlight and decrease the

amount of shade available to the vultures.

Future property owners with retention ponds used by vultures may be able to

discourage vulture bathing by eliminating shallow areas for bathing when other

management options prove ineffective. In doing so they might thus reduce, but not

eliminate attraction of the site to the vultures. Even with deep water, if the vultures have

access, the water might still be an attractant for drinking and possibly for foraging

(Jackson et al. 1978). It is important to consider multi-species management when altering

habitats. The shallow areas attract vultures, but they also provide refugia for fish and

foraging opportunities for wading birds, such as herons and egrets.

3. Roof management. The Center installed bird spikes and motion-activated sprinklers to deter

the vultures from occupying the roof. Both the bird spikes and sprinklers required a high

amount of maintenance. Future management efforts could include the placement of a

vegetative barrier to the west of the building to prevent the creation of the obstruction 85

current. A vegetative barrier, like a hedge would absorb the wind and discourage

additional vulture use of the roof.

Other property owners, who want to discourage vulture use, should construct

buildings with overhanging eaves or plant hedges to absorb wind to prevent the creation

of obstruction currents on their property.

The type of materials used on the roofs may contribute to vulture use of rooftops

as well. The Center roof was covered in asphalt shingles. A metal roof would not provide

the traction needed for the vultures to take off and land. It seems likely that the damage

caused by the vultures would have been less if the roof had been metal. Vulture

excrement could have been removed easily and without further damage caused by the

removal, and the vultures would not have been able to pick apart the roof as they did with

the asphalt shingles.

4. Light pole management. The placement of bird spikes on the light shields did prevent from

vultures perching, however no management occurred on the light poles. Future

management could include the placement of a plastic funnel or small section of bird

spikes on the top of the poles to prevent perching.

5. Air-conditioning unit management. Center personnel were encouraged to enclose the air-

conditioning units to prevent vulture damage, but this was never implemented. Future

management should include the placement of bird spikes along the enclosure or the

complete enclosure of the air-conditioning unit to prevent damage.

6. Management of mowed area. Management of the mowed area included the placement of

monofilament line near the ground to prevent vulture use of the area. Monofilament was

often broke due to the mowing of the lawn. Future management could include stretching 86

monofilament or wire from the fence top to the trees, allowing mowers to access the area

without breaking lines.

An inexpensive solution to preventing vulture use in these areas would be to stop

mowing the grass. There were often times when the Center would not mow the grass for

weeks. When the grass was allowed to grow long, vultures did not occupy the area

because it was difficult to see and maneuver through the longer vegetation.

7. Management of forested area north of Center property. No management efforts could be

initiated in an effort to deter the birds from these roosts since the property was not owned

by the Center. In extreme cases, future management could include habitat modification.

The trees used most often for roosting could be cut down to prevent vulture roosting.

Since the trees were not on Center property, management was not specifically conducted.

The use of the cabbage palms by the vultures suggests that the vultures are capable of

creating their own roost tree sites to some extent.

8. Water pump management. Future management at the Center should include the full

extension of the pipe to the pond, preventing vulture use of the water on the Center

property.

9. Irrigation sprinkler management. The Center and other property owners should use the

irrigation sprinklers for shorter periods of time or after dark; vultures would not be able

to take advantage of this as an additional water source.

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