Temporal Population Dynamics of Important Black Skimmer (Rynchops Niger) and Least Tern (Sternula Antillarum) Colonies in Lee An

Home , Black skimmer, Least tern, Rynchops

Temporal population dynamics of important Black Skimmer (Rynchops niger) and Least Tern

(Sternula antillarum) colonies in Lee and Collier County, Florida

______

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

Courtney E. Kern

2020

Florida Gulf Coast University Thesis

APPROVAL SHEET

This thesis is submitted in partial fulfillment of the requirements for the degree of Master of Science

______Courtney E. Kern

______Kara Lefevre, Ph.D., Advisor

______Brian Bovard, Ph.D, Committee Member

______Edwin M. Everham III, Ph.D, Committee Member

______Adam DiNuovo, Outside Reader

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. 1

Acknowledgements

I wish to thank all the people whose assistance helped me complete this project. Firstly, I am indebted to Dr. Kara Lefevre, who worked with me from beginning to end with my research.

Kara has taken every opportunity to help me succeed. I am incredibly grateful to have her as a mentor, advisor, and friend. I would also like to thank Dr. Brian Bovard and Dr. Win Everham for providing me with the proper guidance throughout not just my research, but my career as a young environmental scientist. Dr. Bovard spent countless hours helping me understand JMP and my data analyses, and Dr. Everham gave me vital feedback on the design of my study.

Additionally, seabird biologist Adam DiNuovo was instrumental in providing crucial background information about the skimmer colonies of Southwest Florida across the timespan of this study.

I also wish to express my appreciation to the Florida Fish and Wildlife Conservation

Commission and Audubon Florida for making it possible to visit these colony sites and be able to work alongside wonderful employees and volunteers. This project would not have been possible without the many members of the Florida Shorebird Alliance. The data collected by this team of biologists and community volunteers is crucial for the understanding of Black Skimmer and

Least Tern ecology. Thank you to the FGCU Whitaker Center for STEM Education and

Audubon Society of Southwest Florida for providing me with the funding that helped me complete my coursework and this project.

Finally, thank you Chad Evers, Brenda Thomas, and Patty Krupp, for being mentors to me throughout my experience at FGCU. I am tremendously grateful for the love and support provided by my parents, Bob and Diane Kern, my sister Maddie Kern, and my fiancée Matt 2

Ramsey. Matt, you have put a smile on my face when I stressed over deadlines and you helped me get through the thick of it. I am so thankful for you!

Abstract

Beach-nesting seabirds are particularly susceptible to environmental changes along coastlines, such as development, beach erosion, human interaction, predation, cyclonic storms, and sea level rise. Measuring all components within an ecosystem is impossible, therefore, selecting components that serve as indicators can provide insight to larger-picture conditions.

Birds have been widely used as biological indicators. Studying populations of imperiled species is essential for understanding long-term trends and creating effective management plans, to achieve conservation goals. Without a baseline assessment of abundance and distribution, it is impossible to determine population status, monitor trends, or support management plans. This study focuses on populations of Rynchops niger (Black Skimmers) and co-nesting Sternula antillarum (Least Terns) due to their vulnerability to coastal land loss, sea level rise, and other human-caused impacts in Southwest Florida. Southwest Florida was selected as the focal area of this study because the region supports a majority of the state’s Black Skimmer population. 16 key sites in Lee County and Collier County have proven to be biologically important for Black Skimmer and Least Tern colonies due to their ecological characteristics that sustain seabird colonies. The Florida Shorebird Database (FSD) is a partner-led program created by the Florida Shorebird Alliance (FSA) for monitoring that consolidates survey effort by a mix of professionals and volunteers, to expedite the evaluation of population goals and management practices. The goal of this study was to gather nest, adult, and fledged chick population data for both seabird species between 2011-2019 to better understand Black Skimmer and Least Tern population dynamics along the Florida Gulf of Mexico Coast. The analysis of Black Skimmer and Least Tern breeding data compiled for 2011-2019 showed that Collier County and Lee

County differed in total nest counts per year. Lee County did not experience as dramatic of peaks 4 and declines compared to Collier County, and Lee experienced more of a steady increase in nests over the years. Consequences of varying rates of reproductive success within the region include: potential population decreases in the future in some areas versus increases in other areas; steady regional populations with some sites contributing recruitment to other sites that have lower reproductive success; abandonment of sites with low reproductive success; and merging of colonies into sites with high reproductive success. As development continues to expand along coastal areas, it is critical that large, ecologically important nesting sites be constantly monitored and maintained. Monitoring is crucial in order to measure the success of management plans and conservation objectives. 5

Table of Contents

Abstract ...... 3 List of Tables ...... 6 List of Figures ...... 7 Introduction ...... 8 Standard Methods of Analyzing Population Data ...... 18 Standard Measures of Productivity ...... 23 Methods ...... 25 Breeding Bird Protocol Description ...... 25 Study Area ...... 25 The Florida Shorebird Database ...... 28 Results...... 36 Relationships Between Nesting ...... 36 Spatiotemporal Dynamics Between Counties ...... 36 Peak Counts of Nests, Fledglings, and Adults ...... 38 Peak Count Windows ...... 39 Discussion...... 48 Methodological Considerations ...... 48 Implications for management ...... 53 Reproductive success ...... 53 Juvenile rates of survival and dispersal ...... 53 Managing Critical Habitat ...... 54 Recommendations for Future Research ...... 56 Closing Notes ...... 56 Literature Cited ...... 58 APPENDIX A ...... 65 APPENDIX B ...... 68 APPENDIX C ...... 71 APPENDIX D ...... 72 APPENDIX E ...... 74

List of Tables

Table 1. Count window calendar for shorebird surveys as established by the Breeding Bird Protocol for Florida’s Shorebirds and Seabirds...... 17

Table 2. Location of study colonies in Southwest Florida...... 27

Table 3. Black Skimmer Wilcoxon/Kruskal-Wallis Tests (Rank Sums) for year (a) and county (b)...... 45

Table 4. Least Tern Kruskal-Wallis Tests (Rank Sums) for year (a) and county (b)...... 46

Table 5. Nonparametric Comparisons For All Pairs Using Steel-Dwass Method for Black Skimmer fledglings between years (2011-2019) ...... 47

Table 6. Nonparametric Comparisons For All Pairs Using Steel-Dwass Method for Least Tern fledglings between years (2011-2019)...... 47

Table 7. Peak Least Tern nest, fledged, and adult counts for Collier County...... 65

Table 8. Peak Least Tern nest, fledged, and adult counts for Lee County...... 65

Table 9. Total peak number of Least Tern nests, fledglings, and adults for both Lee and Collier counties combined...... 66

Table 10. Peak Black Skimmer nest, fledged, and adult counts for Collier County...... 66

Table 11. Maximum Black Skimmer nest, fledged, and adult counts for Lee County...... 67

Table 12. Total peak number of Black Skimmer nests, fledglings, and adults for both Lee and Collier counties combined...... 67

Table 13. Least Tern nest count windows by week beginning at initiation date for each year. ... 68

Table 14. Black Skimmer nest count windows by week beginning at initiation date for each year...... 69

Table 15. Total number of Least Tern nests (all sites included) by the first date of each count window...... 70

Table 16. Total number of Black Skimmer nests (all sites included) by the first date of each count window...... 70

Table 17. Total Black Skimmer and Least Tern nests, fledged, and adults per site (all years added together) with number of years each site was active...... 71

List of Figures

Figure 1. Range of Black Skimmer in North America (Cornell University, 2019)...... 15

Figure 2. Range of Least Tern in North America. (Cornell University, 2019)...... 16

Figure 3. Map of all colony sites occupied by Least Terns and Black Skimmers within Lee and Collier county...... 30

Figure 4: Relationship between number of Least Tern and Black Skimmer nests in Southwest Florida from 2011-2019...... 41

Figure 5. Linear regression analysis of mean number of Least Tern nests surveyed in 16 southwest Florida colonies during 2011-2019...... 42

Figure 6. Linear regression analysis of mean number of Black Skimmer nests surveyed in 16 southwest Florida colonies during 2011-2019...... 42

Figure 7. Least Tern and Black Skimmer nest counts by nth day of the year...... 72

Figure 8. Peak Least Tern nests on the nth day of the year by county (a) and Peak Black Skimmer nests on the nth day of the year by county (b)...... 73

Figure 9. Peak nest counts combined for all sites in Lee county (orange) and Collier County (blue) for Black Skimmers and Least Terns...... 74

Figure 10. Peak fledged counts combined for all sites in Lee county (orange) and Collier County (blue) for Black Skimmers and Least Terns...... 75

Figure 11. Peak adult counts combined for all sites in Lee county (orange) and Collier County (blue) for Black Skimmers and Least Terns...... 76

Figure 12. Peak total nest counts for Black Skimmers and Least Terns...... 77

Figure 13. Peak total fledgling counts for Black Skimmers and Least Terns...... 78

Figure 14. Peak total adult counts for Black Skimmers and Least Terns...... 79

Introduction

Development along the Gulf of Mexico coast of Florida has resulted in an overall decline in habitat available for nesting seabirds. Extensive development over time has reduced the availability of sandy beach habitat upon which colonial seabirds rely. Species that have inhabited this region for centuries have been exposed to magnified pressures over a short period of time that previous generations lived without (Burger, 1989). For example, beach erosion has diminished the amount of natural sand that exists above high tide lines (Downing, 1973).

Humans are spending more time on the beach, making most of the remaining beaches intolerable to nesting seabirds. Bare sand is a requirement for nesting, but vegetative succession makes bareness a temporary condition (Downing, 1973). This change in available habitat means birds must move every few years to new habitats that may present different environmental risks.

This study focuses on the outcomes for populations of two species, Rynchops niger and Sternula antillarum, due to their vulnerability to coastal land loss, sea level rise, and other human-caused impacts (Remsen et al., 2019). Another reason for studying coastal species is that their nesting ranges inherently constrain their population sizes, making estimation of abundances more achievable when compared to species with widespread inland distributions that are not exposed to the same threats (Remsen et al., 2019). Studying seabird populations is beneficial for the assessment of conservation impacts and the implementation of management decisions.

When creating goals for ecosystem conservation, there is a need to evaluate ecosystem conditions and decide when active management is required (Kushlan, 1993). Measuring all components within an ecosystem is impossible, therefore, selecting components that serve as indicators helps provide insight to larger-picture conditions (Kushlan, 1993). Birds have been 9 widely used as biological indicators and have also been used as indicators of ecosystem function at the population level (Kushlan, 1993). Colonial waterbirds such as ibises, herons, storks, gulls, and terns have particularly been studying in order to assess overall environmental conditions

(Kushlan, 1993). The Black Skimmer (R. niger) and Least Tern (S. antillarum) are considered bioindicators due to their susceptibility to negative anthropogenic influences (Remsen et al.,

2019).

Continuing to study the population ecology of imperiled species is essential in order to understand long-term trends and create effective management plans for them. Current population estimates are the foundation of a population conservation strategy (Remsen et al., 2019). Without a baseline assessment of the abundance and distribution, it is impossible to determine population status, monitor trends, or support management plans (Gore, 1991). For North American birds, population estimates of endangered species are fundamental components of any recovery plan

(Remsen et al., 2019). In order to effectively determine both presence and abundance, it is particularly important to study smaller populations (Rout, Heinze, & McCarthy, 2010). Smaller populations of Black Skimmers and Least Terns may be more vulnerable to environmental stochasticity than larger ones (Boyce, 1992).

Black Skimmers (R. niger) are coastal migratory birds with three distinct subspecies

(Viera, Furness, and Nager, 2018). Details of the following species description come from

Burger (2018). Named for their feeding behavior, Black Skimmers fly just above the water with their bills barely cutting the surface, skimming over saltmarsh creeks and lagoons. They are waterbirds with distinctive black feathers above and white below, and a red bill that is black tipped. Their unique bill structure and feeding method sets them apart from other seabird species.

They are tactile feeders, clamping down on prey with the upper mandible when a food item is 10 encountered. They exhibit sexual dimorphism, with males nearly a third larger than females and the lower mandible of the male being much longer.

Black Skimmers breed from Massachusetts south along the Atlantic and Gulf coasts to southern Mexico, as well as on Caribbean islands and southern California (Burger, 2018; Figure

1). A substantial amount of the global population of Black Skimmers breeds along the Gulf of

Mexico coast (Burger, 2018). The North American race that is a focal species of this study, (R. niger) is almost entirely coastal (Gochfeld et al., 2020). Historically, Black Skimmers nested along much of Florida’s coast north of Charlotte Harbor on the Gulf Coast and north of Brevard

County on the Atlantic Coast (FWC, 2013). However, nesting along the entire east coast is now rare, and occurs with limited reproductive success (FWC, 2013). Birds breeding in Florida are considered residents and are joined by migrants from the northern part of the range during the breeding season (Burger, 2018; Figure 1). The populations of this species are decreasing in North

America, and it is listed as a threatened species in Florida (Logan, 1997; Viera et al., 2018;

FWC, 2013). Although attempts have been made to confidently estimate the number of Black

Skimmers along the Florida Gulf Coast, the population size remains uncertain, as well as their migratory patterns (FWC, 2013). These colonial seabirds are particularly vulnerable because they nest on the ground and do not commonly exhibit sufficient antipredator behavior (Burger,

1984). Factors that influence the reproductive success of Black Skimmers include predation, human disturbance, food availability, pollutants, weather and flooding, vegetative succession, and habitat loss (Coburn et al., 2001). Black Skimmers are widespread and usually associated in colonies with other species, such as terns and gulls (Viera et al., 2018). Perhaps as a result of the threats they face, Black Skimmers have become established in alternative habitats, like rooftops, where they may nest in colonies with Least Terns (Coburn et al., 2001). Black Skimmers nest in 11 colonies that range in size from a few to several hundred pairs (FWC, 2013). Colonies are notoriously unsettled at the beginning of the breeding season and may move several times before egg laying is initiated (FWC, 2013). Upon hatching, the altricial young are brooded continuously during the first week by both parents (FWC, 2013). They benefit by nest protection provided by their aggressive neighbors, when Least Terns mob and attack potential predators (Burger, 2018).

For this reason, colony site selection may be more related to the presence of other species

(Burger, 2018). Colony sites that are unsuccessful are often abandoned (Burger, 2018).

In Florida, Least Terns and Black Skimmers are primarily found along sandy beaches, inlets, and estuaries. They regularly nest along the northern Gulf Coast of Florida, but the number and size of their colonies has not been well documented (Clapp et al., 1983, Spendelow

& Patton, 1988). Both species are also found in interior parts of Florida, particularly near freshwater lakes and manmade bodies of water. Breeding habitat includes sparsely vegetated beaches and gravel rooftops. Least Terns and Black Skimmers both forage in shallow waters immediately offshore, estuaries, and impoundments as well as bodies of fresh water. For both species, the wrack line is considered an important habitat component at various life stages. The wrack is defined as organic matter that washes onto the shore and is an integral component of shoreline ecosystems, providing habitat for macroinvertebrates and nutrients to upland terrestrial communities (Harris et al., 2014). Coastal vegetation such as sea oats (Uniola paniculate) and railroad vine (Ipomoea pescaprae) provide crucial foraging and sheltering habitat for chicks

(FWC, 2013).

Black Skimmers, like many other seabirds that feed mainly on fish, suffered population declines due to oil and organochlorine chemicals during the 1960s and 1970s (Burger, 2018).

While contaminants in the Gulf declined by the early 1980s, Black Skimmers are still declining 12 along the Texas coast (Burger, 2018). Similarly, the number of breeding Black Skimmers in

Louisiana colonies dropped due to erosion of preferred nesting areas, human disturbance, and a decrease in the number of available sites (Burger, 2018). Statewide declines are also indicated in

Florida. The number of Black Skimmers nesting along the Atlantic and Gulf coasts is approximately 90,000 to 101,000 individuals, or 50,000 pairs (Burger, 2018). There are another

4,200 pairs in California and the Pacific coast of Mexico (Burger, 2018). Only a few dozen pairs breed in the Yucatán and are combined with large numbers of northern migratory Black

Skimmers in the winter (Burger, 2018). Breeding Bird Surveys show steep declines in Alabama,

Louisiana, and Florida, with Texas numbers slightly increasing (Burger, 2018).

Black Skimmers are known to exhibit nest site fidelity, which is the tendency to nest in the same place within the colony site each year (González-Solís et al., 1999). Black Skimmers delay breeding until they are 3-4 years old, lay an average of four eggs, and live an average of

10-15 years (Burger, 2018). Breeding behavior usually begins near the last week of March each year and egg-laying can begin between mid-April and mid-May (White et al., 1984). If nesting attempts fail, they will usually renest within a week or so, but not usually after early August

(White et al., 1984). Reproductive success is often quite low, since they nest on ephemeral habitats or beaches exposed to flood tides and anthropogenic activities (Burger, 2018).

The Least Tern is the smallest American tern, characterized by a black-capped crown, white forehead, black-tipped bill, grey back and dorsal wings, white belly, and orange legs.

There are three U.S. subspecies which are nearly indistinguishable morphologically and are currently distinguished by their breeding ranges (Whitman, 1988). The sexes are virtually identical, however Boyd (1984) has developed criteria for identifying the two sexes. The interior population of Least Terns extending from Texas northward to North Dakota was placed on the 13

Endangered Species list in 1985 and is protected under the Migratory Bird Treaty Act (Whitman,

1988).

The Least Tern is a migratory species that nests along freshwater habitats of the Missouri and Mississippi rivers and their tributaries as well as coastal regions in the U.S. (USFWS, 2020;

Figure 2). Least Terns arrive at breeding grounds anywhere between mid-May to late-April

(Whitman, 1988). Departure has been recorded to occur from late July to early September

(Whitman, 1988). Terns choose sites that are well-drained and far from the water line (Whitman,

1988). Like the Black Skimmer, Least Tern nests are constructed by scraping a depression in the sand. Coastal populations have been documented to nest on gravel rooftops of buildings

(Whitman, 1988). Least Terns are notorious for mobbing potential predators to a colony, which gives species like the Black Skimmer, snowy plover, and piping plover, who nest amongst Least

Tern colonies and are not known to show antipredator behavior, protection from threats

(Whitman, 1988).

Least Terns, like Black Skimmers, are known to exhibit nest-site fidelity, which is known to be influenced by previous breeding success (González-Solís et al., 1999). Changes in dispersal and pair bond status have been extensively studied between breeding seasons, but not within- season (González-Solís et al., 1999). Furthermore, increased breeding dispersal and pair divorce rates can be expected when birds renest after a first breeding attempt has failed (González-Solís et al., 1999). For Least Terns, the interval between loss of eggs and renesting has been documented to be as soon as 4 days but up to 16 days. (Massey & Fancher, 1989). After chick loss, the interval has been documented at 5-12 days (Massey & Fancher, 1989). Nesting success for interior Least Tern colonies has ranged from 2.8% to 100% (Whitman, 1988). Hager (1937) 14 reported a 9 percent survival rate for a colony of eastern Least Terns. California Least Terns have had fledging success rates of 11% to 50% (Swickard, 1971; Massey, 1972).

Least Terns, which have a stronger preference for sparsely vegetated beaches (Burger &

Gochfeld, 1990b), have historically used alternative nesting habitats when available, such as dredged spoil islands. The reduced maintenance of these islands has in recent decades resulted in a majority of New Jersey’s population nesting on beaches (Erwin et al., 2003). Thus, many terns share breeding space with beach recreationists. People often gather near colonies and can approach to within feet of the colony edges, which can sometimes elicit flushing and defensive behavior from the terns (Mendillo, 2009). Depending on how long terns are flushed from the nest, reduced hatching may occur (Mendillo, 2009). Further, prolonged stress responses have been shown to result in reproductive failure, immune system repression, impaired growth, and other health problems (Mendillo, 2009).

Figure 1. Range of Black Skimmer in North America (Cornell University, 2019).

Figure 2. Range of Least Tern in North America. (Cornell University, 2019).

Table 1. Count window calendar for shorebird surveys as established by the Breeding Bird Protocol for Florida’s Shorebirds and Seabirds (FWC, 2015).

Count Date Primary purpose Reason

Locate early shorebird Many plovers and 1 March 18-24 oystercatchers are on nests by nests. mid-March.

Locate early seabird Some seabird colonies begin 2 April 15-21 colonies; check status forming in early April. of shorebird nests.

Locate new nests & colonies and check 3 May 13-19 status of existing ones. Locate shorebird May and June represent the chicks. peak of nesting season.

Seabird chicks present at most Check the status of all colonies by June.

nests & colonies. 4 June 10-16 Count shorebird and seabird chicks.

Locate new nests & colonies and check July is often the time when 5 July 8-14 status of existing ones. second clutches and renesting Count chicks and attempts are initiated. fledglings.

August represents the tail end Count chicks and of the nesting season when 6 Aug. 5-11 fledglings. recent fledges are most apparent.

The Florida Shorebird Alliance

The Florida Shorebird Alliance (FSA) is a statewide network of partnerships that works to advance the conservation of shorebirds and seabirds in the state. Partners collaborate to research, manage, educate, and create public policy for shorebird conservation

(FWC, 2019a). In 2013, the FSA released the Species Action Plan for Imperiled Beach-nesting

Birds (IBNB), which was developed to improve conservation status for species like the Black

Skimmer (FWC, 2019a). The IBNB sets long-term statewide population goals for Black

Skimmers and outlines conservation plans to tackle threats to this species (FWC, 2019a). The

Florida Shorebird Database (FSD) is a partner-led program created by the FSA for monitoring that consolidates survey effort by a mix of professionals and volunteers, to expedite the evaluation of population goals and management practices (FWC, 2019a). Partners follow the

Breeding Bird Protocol (BBP), which directs them to count birds during specific time windows in each nesting season (FWC, 2019b; Table 1). Data collected by the FSA give insight to population metrics, species distribution, and reproduction outcomes such as nesting success

(FWC, 2019b). These data are used to guide management decisions as well as measure the success of current efforts (FWC, 2019b).

Standard Methods of Analyzing Population Data

Data on the long-term fluctuations in the components of marine ecosystems have both historical and ecological significance: they are important for identifying ecological baselines, understanding ecosystem dynamics, and may ultimately support the prediction of future changes

(Catry et al., 2019). Birds are a key component of many marine ecosystems. In some areas, their populations have been studied for extensive periods and the catalysts for population change are 19 well understood (Catry et al., 2019). However, along the Florida Gulf Coast, relatively few quantitative population studies of marine and coastal birds have taken place.

Because surveys only provide approximations of population size, caution must be taken when using them for population change analyses. Temporal or geographic variation in the proportion of birds counted can be misconstrued as differences in population size (Link & Sauer,

1998). Therefore, these factors must be incorporated as covariables in the analysis of population parameters from count data (Link & Sauer, 1998).

Measuring populations of birds including Black Skimmers and Least Terns has been done in a multitude of ways. The Breeding Bird Survey (BBS) is a cooperative monitoring program that started at the peak of the “pesticide era” more than 50 years ago and is sponsored by the U.S.

Fish and Wildlife Service and the Canadian Wildlife Service (Robbins et al., 1986). It is the most extensive historical database for monitoring bird populations in North America (Bled et al.,

2013). Its main goal is to approximate population trends of the over 400 bird species that nest in

North America and Mexico, many of which migrate across international boundaries (Patuxent

Wildlife Research Center, 2020). It provides data on short-term population fluctuations that can be attributed to specific weather events, recuperation periods following catastrophic declines, typical annual variations, long-term population trends, and invasive species (Robbins et al.,

1986). The BBS also allows for detailed mapping of relative abundance of each species and provides baseline data for comparison to more intensive local studies (Robbins et al., 1986). It can also be used to compare distribution of species by time of year. Observers use standardized methods to survey on one morning each year at the height of the breeding season. The observer records the total number of bird species heard and seen at each stop. Data are summarized, and then evaluated by editors (Robbins et al., 1986). 20

The Breeding Bird Survey standardizes procedures, selects experienced observers, and specifies acceptable weather conditions as much as possible in order to reduce many of the potential sources of bias (Robbins et al., 1986). Possible sources of bias include: the consistency of recorded temperature units, effects of weather on results, date and time dissimilarities in data collection, number of observers, experience of observers, problems with hearing in observers, misidentification, unrecognizable species, number of species, threshold of abundance, changes in survey routes, time spent at each stop, and poor sampling of some species (Robbins et al., 1986).

All sources of bias are recognized and accounted for as much as possible.

A proportional trend is estimated for each route by using linear regression on logarithmic trend transformed data (Robbins et al., 1986). Route trend estimates are weighted by geometric mean counts on the route to approximate bird population trends in an area, a function of number and spacing of the years the route was visited to minimize variance in trend estimates, and the area represented by each route so that equal areas have equal influence (Robbins et al., 1986).

Annual mean counts are used to represent a species average diversity- not the density within suitable habitat. The Breeding Bird Survey provides data that influence models of temporal population change that help to assess bird population variations and trends (Bled et al., 2013).

For waterbirds, a “colony site” is defined as a specific location on a waterbody where focal species nest (Kushlan, 1986). A “colony” is the assemblage of nesting birds at that colony site (McKellar et al., 2019). The goal of using databases to compile population data is to (1) examine the distribution and size of colonies of each species and (2) to establish the degree of overlap in the use of specific colony sites for nesting (McKellar et al., 2019). McKellar and colleagues created a database of historical and current colony sites of colonial waterbirds in the southern region of Canada. Before analysis and mapping, they created a reduced dataset to 21 contain only the locations with known breeding evidence. Restrictions were not placed on the number of individuals required to constitute a colony.

EBird, one of the world’s largest citizen science projects, is a database that uses citizen science to address questions about bird distributions and abundance on large spatial and temporal scales (Bonney et al., 2009). Citizen science possesses the advantages of low cost and ease with which sizeable amounts of data can be collected (Callaghan & Gawlik, 2015). EBird creates a central repository for tens of thousands of people to submit their observations. When a volunteer submits an eBird record, they record the location of the area and, based on the date, eBird generates a list of likely birds to be seen in that region (Callaghan & Gawlik, 2015). The use of a smart phone as a data recording tool is an incentive for participation, since eBird has a mobile app for entering data in the field (Callaghan & Gawlik, 2015). EBird’s popularity and its high level of data integrity have facilitated more than 90 peer-reviewed scientific publications that have either used eBird data or studied features of the project (Sullivan et al., 2014).

Methods of surveying differ depending on the size of the colony being observed. In their literature review, McKellar et al. (2019) identified ground nest surveys done by traversing the colony in parallel transects as the most accurate method, yet it can be time consuming and may cause disturbance if done during incubation as opposed to post-fledging. They pointed out that use of Unmanned Aerial Vehicles (UAVs, or drones) has the advantages of being able to survey a colony quickly, causing less disturbance, and may increase the detectability of smaller species.

An alternative form of aerial survey is the use of planes. The ACP Aerial Breeding

Waterfowl Survey began in 1986 and is flown annually by the USFWS with a pilot observer and a passenger observer (Amundson et al., 2019). Observers count birds as the GPS location and flightpath of the aircraft is recorded. These surveys generate count data which comprise 22 observations of a species along each transect during each year. Observations represent an index to true abundance rather than an estimate of the actual population size (Amundson et al., 2019).

The timing of a survey in a given year influences the indices of abundance. Amundson and colleagues (2019) evaluated spatially explicit population changes of Arctic breeding waterbirds in three different ways. They mapped the geometric mean rate of change in predicted abundance per area for area with greater than or equal to 3 non-zero counts over the 25-year period, they summarized density and trends for the entire study region, and they evaluated whether population growth rate varied over the survey period by conducting a rolling-window analysis where they estimated the geometric mean rate of change over successive 10-year periods beginning each year of the study (Amundson et al., 2019). Population growth was plotted in each period relative to the long-term average for the species.

Marine radar has also been used to survey populations of seabirds in North America.

Marbled murrelets were surveyed during breeding at strategic locations, and a linear trend was created to set nesting and population targets for the Canadian population in British Columbia

(Bertram et al., 2015). Marine radar was concluded to be a robust method for monitoring these seabirds. The marbled murrelet exhibits annual changes in abundance, likely related to ocean foraging conditions affecting breeding success (Bertram et al., 2015). Here, a Bayesian hierarchal model was used, providing a statistically consistent conceptual framework to estimate population trends in each site within each region (Bertram et al., 2015).

In other studies, population models are used to analyze the decline of biodiversity as well as to predict future trends and support management decisions (Ouvrard et al., 2019). Different population dynamic models have been developed in literature to describe overall population trends in a region. Numerical tools allow researchers to model population changes with partial 23 differential equations (PDEs) in order to exemplify historical and spatial dynamics simultaneously (Ouvrard et al., 2019). In France, dynamic models for birds have been used to evaluate different policy scenarios that promote targets for biodiversity up to 2050 (Ouvrard et al., 2019). Accurate models in terms of time and space are necessary to help decision makers take biodiversity goals into account when creating public policies (Ouvrard et al., 2019).

Integrated population models (IPMs) are another type of modelling framework that explicitly integrate demographic information in population models (Zhao et al., 2019). They have advantages in accounting for various sources of uncertainty and offer more accurate estimates of parameters than models that analyze abundance and demographic data separately

(Zhao et al., 2019). Due to the advantages that IPMs present, they have been used in ecological research and are considered a substantial modeling framework for the decision making behind conservation initiatives (Zhao et al., 2019).

Standard Measures of Productivity

Troy (1996) measured the reproductive success of shorebirds breeding in Arctic Alaska, using the Kruskal-Wallis test to detect significant differences in nest initiation dates. Burger et al.

(1994) studied population dynamics of Least Terns and Black Skimmers in the Northeastern U.S.

They determined reproductive success in each colony by dividing the number of fledglings by the number of nests (pairs). Then, they used an ANOVA followed by a Tukey’s test to compare reproductive success among regions. Cohen, Houghton, & Fraser (2009) also used an ANOVA to compare continuous variables among years and between sites when looking at the reproductive success of piping plovers. Hartman & Oring (2009) were able to determine long- billed curlew fledging success by banding chicks. By doing so, they included individual covariates of chick weight, size (tarsus length), and body condition of chicks. Further, McGowan 24 et al. (2005) described productivity to be the number of chicks fledged per breeding pair per year. They calculated the standard error of productivity by averaging the number of chicks fledged by each pair that attempted to nest, and then calculating the variance of that average.

This estimate of productivity assumed that the local breeding number remained constant during the breeding season and that pairs retained their breeding territories. Similar to my study, many birds in their study were unmarked. However, observations of marked birds and other studies of these species supported their assumptions (Nol & Humphrey, 1994).

My study aims to examine how regional measurements of Black Skimmer and Least Tern nests, fledglings, and adults along the Florida Gulf Coast change with time. Another objective is to determine whether these temporal changes differ by region, in this case, Collier versus Lee counties, and whether the number of Least Tern nests influence Black Skimmer breeding success. Further, I evaluate which sites are of greatest importance for the breeding biology of these birds. Ultimately, the goal is to establish whether regional measures of nests and fledglings between these two species change over time, if these temporal changes vary by region, and if presence of Least Tern co-nesting influences breeding success of Black Skimmers in those areas.

Data recorded from 2011-2019 in the Florida Shorebird Database are utilized to denote numbers of nests, fledglings, and adult birds along 16 key sites in Lee and Collier counties.

Methods

Breeding Bird Protocol Description

The shorebird nesting season in Florida generally starts in mid-February and regular surveys are conducted until mid-August. Observers are required to survey once per month during count windows : March 18-24, locate early shorebird nests; April 15-21, locate early seabird colonies and check status of shorebird nests; May 13-19, locate new nests and colonies and check status of existing nests as well as locate shorebird chicks; June 10-16, check the status of all nests and colonies and count chicks; July 8-14, locate new nests and colonies and count existing ones; and August 5-11, count chicks and fledglings (Table 2). Count windows occur on the same dates each year, to provide consistency for shorebirds and seabirds. More frequent surveys are recommended for better tracking of populations (Florida Fish & Wildlife

Conservation Commission, 2015).

Study Area

This study included Black Skimmer and Least Tern colonies located within Lee County and Collier County, Florida, situated along the Gulf of Mexico. Sites were mapped on Google

Earth Pro to visualize spatial coverage in site selection. These counties are historically important breeding regions for both species. FWC defines a colony as “a congregation of 1 or more pairs of breeding birds that nest and roost in close proximity at a particular location” (FWC, 2013).

Colonies may contain multiple species. The sites included Big Hickory Island, Big Marco Pass,

Bowditch Beach, Captiva Island, Carlos Pointe Beach, Caxambas Pass, Cayo Costa State Park,

Gasparilla Island, Keewaydin Island, Kice Island, Lover’s Key State Park, Morgan Beach, New

Beach, Sanibel Island, Second Chance, and the Ten Thousand Islands (Table 2). Most of the study sites were flat, open, unobstructed sand beaches or islands, which enabled visual estimates 26 and contributed to low interobserver variability (Burger et al., 1994). When colonies were undisturbed, Black Skimmers and Least Terns continued to incubate and could be counted while they incubated (Burger et al., 1994). A site was defined as a location of past or present colonial nesting.

In Google Earth Pro, northernmost sites were differentiated from southernmost sites. The coastal length encompassing the northern half of the sites was about 26.01 miles long, and the length of the southern half was about 18.13 miles long (Figure 3). The total distance between

Gasparilla Island (northernmost site) and the Ten Thousand Islands (southernmost site) is about

77.8 miles. Distinguishing a northern half and a southern half made comparisons between the two regions easier for this study.

Table 2. Location of study colonies in Southwest Florida.

Site Name County Location

Big Hickory Lee 26°22'9.30"N 81°51'29.32"W

Big Marco Pass Collier 25°58'2.43"N 81°44'45.35"W

Bowditch Lee 26°27'50.76"N 81°58'5.18"W

Captiva Lee 26°31'39.28"N 82°11'41.33"W

Carlos Pointe Lee 26°24'9.87"N 81°53'10.38"W

Caxambas Collier 25°54'31.36"N 81°42'31.81"W

Cayo Costa Lee 26°38'41.47"N 82°14'16.48"W

Gasparilla Lee 26°45'7.23"N 82°16'0.96"W

Keewaydin Collier 26° 5'18.24"N 81°47'59.98"W

Kice Island Collier 25°52'53.41"N 81°41'38.34"W

Lovers Key Lee 26°23'16.78"N 81°52'38.92"W

Morgan Beach Collier 25°51'16.13"N 81°41'28.32"W

New Beach Collier 25°51'54.49"N 81°41'44.22"W

Sanibel Lee 26°25'55.39"N 82° 6'48.96"W

Second Chance Collier 25°50'24.04"N 81°40'2.71"W

Ten Thousand Islands Collier 25°51'18.63"N 81°29'33.43"W

The Florida Shorebird Database

The source of data used in this analysis is publicly available and can be accessed through the Florida Shorebird Database. Approximately once a year from 2011-2019, the Florida

Shorebird Alliance (consisting of 12 ornithological research partnerships around the state) collaborated to conduct shorebird surveys during the breeding windows. Most of these surveys

Count windows occur during the breeding season for seabirds and shorebirds- between March and August. Routes are surveyed from established start point to end point, with observers completing a route form and entering all data into the FSD. New colonies are recorded with the longitude and latitude of each, using a GPS unit. Each site is given a descriptive name including the species, location, and nest sequence (FWC, 2015).Route forms are completed after each route is surveyed, and all data are entered into the Florida Shorebird Database. FSA works by utilizing an adaptive management framework (FSA, 2020). Long-term monitoring, a critical component of adaptive management, enables the study of abundance, distribution, and productivity of shorebirds and seabirds (FSA, 2020). Monitoring also permits the studying of impacts of various factors like predation and habitat loss. Based on these data, partners within the FSA can implement strategies to manage and conserve native shorebird populations in the region (FSA,

2020).

The Florida Shorebird Database (FSD) is a method of collecting occurrence and reproductive data on six focal species of nesting shorebirds and 14 species of colonial nesting seabirds, including the Black Skimmer and Least Tern (FWC, 2019a). This database is managed by the Florida Fish and Wildlife Conservation Commission (FWC) and is a free online resource for this information (FWC, 2019a). The purpose of the FSD is to monitor long-term trends of shorebird and seabird populations across the state. Biologists can use these data to determine 29 distribution, status, and trends for various species in the state (FWC, 2019a). In 2010, FWC collaborated with multiple partners to reconstruct the Florida Beach-Nesting Birds Website, which was launched in 2005 (FWC, 2019a). Now, the FSD serves as a tool that can provide answers to crucial questions about the status of shorebirds and seabirds in the state (FWC,

2019a).

Seabird colonies are recorded in a Seabird Colony Form. Nests are identified by counting adult birds in incubating posture, omitting those merely standing in the colony. Each incubating adult is considered as one nest. Black Skimmers that are incubating may be difficult to identify because they dig scrapes to rest, so scraping does not always equal nesting. Incubating posture can be recognized by an upright posture and elongated neck. As eggs hatch, adults begin to brood young. This can also make it difficult to determine whether a Black Skimmer is incubating, so brooding behavior is also counted as a nest. All incubating birds within sight of the colony boundaries are counted on the Seabird Colony Form. A colony is Active when a nest of any species is present, and remains Active until all nesting adults, chicks, and fledged juveniles have left (FWC, 2015).

Direct Counts are done using binoculars or a spotting scope to count individuals within a colony. The average of at least two counts are reported for each colony nest count. The same method is used to count chicks. Estimate Counts are conducted in situations when the observer is not able to conduct a Direct Count. A section of the colony is delineated as the count area. A

Direct Count of this area is conducted and extrapolated to determine an estimate for the remaining percentage of the colony (FWC, 2015).

Presence/Absence and Did Not Check: Presence is indicated when nests or chicks are seen but not counted. If the area is searched but no nests or chicks are seen, Absent or “0” is 30 recorded. If the presence or absence of chicks or nests cannot be verified, Did Not Check is recorded (FWC, 2015).

Northern portion of sites

Southern portion of sites

Figure 3. Map of all colony sites occupied by Least Terns and Black Skimmers within Lee and Collier county. Northern and southern portions of sites shown.

Black Skimmer and Least Tern occupancy data for Lee and Collier nesting sites were obtained from the FSD. When exported to EXCEL, the FSD data was organized by Survey Year,

Site Name, Coordinates of the Site, Total Visits to Site, Reported Status of Site, Species Present,

Maximum Nests, Maximum Downy Chicks, Maximum Feathered Chicks, Maximum Flight-

Capable Chicks (Fledged), and Maximum Adults. For the purpose of this study, downy and feathered chick counts were excluded. Each site name entered in the database was recoded based on its geographical coordinates for consistency because in many cases, colony sites were referred to by different names by different members of the FSA that entered count data. The listed coordinates were used to verify the region of each colony. Colonies were grouped into the 16 sites. If one site could experience different environmental influences than another, they were considered separate.

The earliest available data for the selected sites and species in the FSD was from 2011.

Data from 2020 was not finalized at the time of analysis for this study. Due to discrepancies in training, expectations, and abilities of observers, data from 2011-2014 were commonly characterized by estimate counts, rather than the more precise direct count method. This was considered when sorting through the FSD.

The data were sorted into two separate tables - one for Least Terns and one for Black

Skimmers. Each table was broken down into Colony, County, Species, Year, Initiation Date,

Fail/Completion Date, Maximum Nests, Maximum Fledged, and Maximum Adult Counts. The

Initiation Date is described as the first date where nests were recorded at that site. This is also described as the date the first egg is laid (Troy, 1996). The earliest Initiation Date for Least Terns was April 17th, and the earliest Initiation Date for Black Skimmers was May 14th. The

Fail/Completion date is described as the date when nesting stops, or all chicks have hatched. 32

Ideally, colonies will nest until completion, or for the duration of a full nesting season. This could be as a result of a nesting failure, perhaps due to predation, storm, or tide event.

Nests, adults, and flight-capable juveniles were considered to be the measurements most indicative of success at each of these sites (Burger et al., 1994).

Peak nests, fledged, and adult counts were extrapolated from the FSD for each site, for both species, annually between 2011 and 2019. Peak (highest) counts were considered to be more accurate than minimum counts or means (Burger et al., 1994). Minimum counts underestimate the number of nests per season. Using the mean of all recorded counts for that site and year is not accurate because it underestimates the peak count for that season (Drury, 1973).

A count of nests made at any one time does not take into account the early clutches that have been lost, late clutches not yet laid, adult birds out foraging, or birds moving between colonies

(Drury, 1973). Nesting initiation dates were documented by looking at the first recorded nest in the FSD for each year and colony site. Initiation dates show what time of year the birds began nesting and allowed for the comparison to initiation dates provided in the literature. Then, nest failure/completion dates were documented. If nesting ended earlier than the typical completion date window, it was considered a failure. Failures may occur due to a variety of environmental factors such as predators, human activity, flooding, or storms. If nesting stopped on a date that was considered normal and not too early on in the season, it was recorded as a complete, or successful, nesting attempt.

EXCEL was used to create a spreadsheet for each documented entry for nests. All sites in which birds nested were graphed based on the visit date and the number of nests for both Lee and

Collier. Having all documented nests from both species on one graph made it more effective to 33 examine when peak nesting dates were. Graphing all documented nests, not just the peak counts, provided a visual for nest count densities along the given timeline.

Weekly counts were inspected, selecting the greatest number of nests (or pairs) in order to estimate colony size. Peak fledglings were recorded for each count window per site. Then, each instance where a colony nested, but did not produce fledglings, was removed from the dataset. After a nesting failure, birds will nest again on the same site or move to another site. By counting only the instances where nesting and fledging occurred, it is much more likely that birds are not being recounted.

These instances were removed from the dataset because they may have deleterious effects on any statistical analyses performed. These cases may also seriously bias or influence estimates that could be of practical interest (Osborne & Overbay, 2008). Judd & McClelland (1989) make several strong arguments for removal in these cases in order to get the most authentic estimate of population parameters possible. However, not all researchers agree on this reasoning (e.g., Orr,

Sackett, & DuBois, 1991). It should be noted that data cleaning can never be a remedy for poor study design or study conduct. Yet, all studies, no matter how well designed or implemented, have to deal with errors from various sources and the effects they have on study results (Van den

Broeck, 2005). Little guidance is currently provided in the peer-reviewed literature on how to set up and carry out data cleaning in an efficient and ethical way, and the data cleaning process has not been described or studied comprehensively (Van den Broeck, 2005). This is a case where scientists must use training, intuition, rational argument, and thoughtful consideration in decision making (Osborne & Overbay, 2008). Although some authors argue against the removal of data, they are in the minority, particularly when the data are illegitimate (Osborne & Overbay, 2008). 34

The benefits of data cleaning extend to simple and multiple regression as well as different types of ANOVA procedures (Osborne & Overbay, 2008).

After removing instances where fledging did not occur, EXCEL was used to create a spreadsheet for just the peak nesting date ranges based on the weekly counts mentioned.

Although using peak nesting dates captures the highest number of nests counted on a day in a given year, it does not take into account the nests that were laid before or after the peak date. A way to alleviate this issue is to select count windows for each species beginning at the earliest initiation date and determine the highest number of nests per window. Each window spanned one week beginning at the earliest initiation date for that year. For example, the initiation date for

Least Terns in 2011 was April 19th. Therefore, the first window for 2011 was April 19th-April

26th. The next window began on April 27th, and so on. Peak count windows varied depending on the year. In some years, seabirds nested earlier than others, and vice versa. Next, each peak nest count per window was added together to get a sum of the peak nest numbers for that year. So, the total cumulative peak nest count for Least Terns in the first count window of 2011 was 805 nests.

This method more accurately represents the true number of nests in a season. Total peak nest counts for each site were categorized based on the county they were located in. For graphing, dates were translated into nth days of the year using a formula in Excel.

The sites with the peak number of nests and fledglings were pulled from the original dataset for each species. Burger et al. (1994) estimates overall reproductive success of a colony by dividing the number of fledged young by the number of pairs nesting in the colony (nests).

They argued that this method caused the least amount of disturbance to a colony and yields results comparable to other estimates. The number of fledglings was divided by the number of nests in Excel, providing a measure of reproductive success for each year. 35

Statistical analyses were performed in JMP. Nesting data violated the assumptions of the

ANOVA and could not be transformed, so a Kruskal-Wallis non-parametric test was used to determine differences in fledge counts between years. A Wilcoxon nonparametric test was used to evaluate differences in the number of fledged birds between counties, because there are only two treatment levels for county (Lee and Collier). EXCEL was used to compare peak fledged counts between the two counties from 2011-2019. Next, a correlation analysis was performed to determine whether Black Skimmer nesting success is determined by the presence of Least Terns.

Then, a linear regression was performed for each species to look at colony size over time.

Number of nests was used as a parameter for colony size.

Results

Relationships Between Nesting

A correlation analysis was performed to determine the relationship between Black

Skimmer and Least Tern nesting in the study sites in 2011-2019 (Figure 4). Black Skimmers tend to show up to nest later in the nesting season than Least Terns do, often times choosing colony sites where terns are already nesting. After conducting the correlation analysis, it was concluded that Least Tern nests have little to no influence on the number of Black Skimmer nests in a colony (r2=0.0075). While the number of Least Tern nests that are present at a colony site may not directly influence the absolute number of Black Skimmer nests, it may tempt Black

Skimmers to choose certain nesting sites over others.

Linear regression analyses were done for mean colony size (number of nests) per year for both species. R2= 0.1796 for mean least tern nests per year, and r2=0.5348 for mean black skimmer nests per year (Figures 5&6). 2015 showed a major drop in the number of Least Tern nests, which may be attributed to a spike in predation for that year. Both species seemed to experience declines in 2018, which was a particularly bad year for red tide in the region. In each of the regression analyses done, low r2 values are reported. These datasets have an inherently large amount of variation, causing the r2 values to be low.

Spatiotemporal Dynamics Between Counties

All nesting attempts were plotted to compare the two species’ nesting dates. Between

2011-2019, there were many instances of nesting. By looking at the first day a nest was made, it was clear that Least Terns do nest earlier in the season than Black Skimmers (Figure 7, in

Appendix D). 37

The highest documented Least Tern nests per nth day of the year were plotted, rather than plotting every nesting instance. When looking at peak nests, it is apparent that there have been higher nest counts in Collier than Lee (Figure 8a, in Appendix D).

When the same was done for peak Black Skimmer nests, similar conslusions could be made. Collier has been shown to have higher nest counts for both bird species. Black Skimmers do not experience as high of nest counts, and seem to have much higher peak numbers in Collier than in Lee (Figure 8b, in Appendix D).

The analysis of Black Skimmer and Least Tern breeding data compiled for 2011-2019 showed that Collier County and Lee County differed in total nest counts per year. Lee County did not experience as dramatic of peaks and declines compared to Collier County, and Lee experienced more of a steady increase in nests over the years (Figure 9, in Appendix E).

Collier County has had much higher spikes in the number of fledged birds, particularly in

2013 and 2016. Interestingly, 2013 and 2016 were two of Lee County’s worst years for Black

Skimmer fledglings, when numbers were much higher in Collier during those same two years, indicating a major spatial difference. Collier experienced the highest Least Tern fledgling counts in 2017, and the lowest in 2015 and 2018. Collier experienced the highest Black Skimmer fledgling counts in 2016, but the lowest in 2012 and 2015. Lee Least Tern fledgling counts were highest in 2013 and lowest in 2011, and Lee Black Skimmer fledgling counts were highest in

2018 and lowest in 2011-2013 (Figure 10, in Appendix E).

Overall, more adult birds were counted in Collier versus Lee County (Figure 11, in

Appendix E). Both species seemed to follow similar patterns for the counties they were located in. Adults of both species experienced increases in Collier County for 2018.

When the total nest counts were added together for each county, it was evident that both 38 species, regardless of county, suffered declines in nests during 2015. Both seemed to peak in

2016, and then begin to taper down in the following years (Figure 12, in Appendix E).

Total fledged chick counts were added together for both counties. While fledged counts were quite variable among the years, it is evident that 2012 and 2015 were considerably low years for both species. Conversely, both species experienced increased fledged counts in 2013 and 2016. Black Skimmers experienced high fledged counts in 2018 between both counties, while the opposite was true for Least Terns. During this year, Least Terns left their large colony sites in Big Marco and their whereabouts were undocumented. This has been thought to be attributed to the particularly serious red tide event during the summer of 2018 (Figure 13, in

Appendix E).

Adult birds among counties were combined for each species. Independent of county, both species experienced declines in the number of adults in the year 2014. In 2016, adult counts of both species were high (Figure 14, in Appendix E). In 2018, a major red tide event caused Least

Terns to migrate to other sites that were not documented. It is unknown where the majority of these adult Least Terns moved during that summer.

Peak Counts of Nests, Fledglings, and Adults

The peak annual number of Least Tern nests in Collier county between 2011 and 2019 ranged from 184 (2019) to 892 (2012). In Lee county, counts of Least Tern nests ranged from

188 (2012) to 515 (2015). The abundance of Collier Least Tern fledglings ranged from 5 (2015) to 341 (2017), and Lee Least Tern fledglings ranged from 26 (2011) to 259 (2019). Counts of

Collier Least Tern adults ranged from 183 (2011) to 1544 (2016; Tables 7&8, in Appendix A).

The peak count of Least Tern nests in both counties combined was highest in 2016 with

1176 nests, and lowest in 2019 with 550. The total number of Least Tern fledglings was highest 39

in 2013 with 454 nests and lowest in 2018 with 92. The total number of adult Least Terns was

highest in 2012 with 1969, and lowest in 2011 with 707 (Table 9, in Appendix A).

The peak count of Black Skimmer nests in Collier county ranged from 139 (2012) to 784

(2017). In Lee county, the number of nests ranged from 44 (2011) to 450 (2016). The number of

Collier Black Skimmer fledglings ranged from 0 (2012, 2015) to 536 (2016) and Lee Black

Skimmer fledglings ranged from 0 (2011, 2012, 2013) to 112 (2018). The number of Black

Skimmer adults ranged from 739 (2014) to 2522 (2018) in Collier, and from 44 (2011) to 450 in

Lee (2016; Tables 10&11, in Appendix A).

The peak count of Black Skimmer nests in both counties combined was highest in 2016 with 1037 nests, and lowest in 2011 with 331, which was similar to the Least Tern trend for those years. The total number of Black Skimmer fledglings was highest in 2016 with 537 nests and lowest in 2012 with 0. The total number of adult Black Skimmers was highest in 2018 with 2851, and lowest in 2014 with 947 (Table 12, in Appendix A).

Peak Count Windows

For Least Terns, the window with the highest number of total peak nests was the week of

4/24/16-5/1/16, with 816 nests surveyed among all sites. During this window, there were 1,567

adult Least Terns counted, which roughly translates to 2 adults per nest (Table 13, in Appendix

B).

The median peak nesting count date was determined for both species. For Least Terns,

that was day 114 — depending on the year, this translates to about April 24th (Table 13). For

Black Skimmers, the median peak nesting day of the year was 138, which usually falls on May

18th (Table 14, in Appendix B).

The count window in each year with the highest amount of Least Tern nests seemed to be the last week in April. The earliest initiation date for Least Terns was 4/17/12 and the latest initiation date was 5/25/2018 (Table 15, in Appendix B). The count window in each year with the highest amount of Black Skimmer nests fell in the middle of May. The earliest initiation date for Black Skimmers was 5/14/15 and the latest was 5/28/14 (Table 16, in Appendix B).

Of the 16 sites, Big Marco Pass had the most nests, fledglings, and adult birds of both species. Total nests ranged from 2 to 58,164 individuals, total fledged ranged from 0-11,605 individuals, and total adults ranged from 12 to 185,053, which is about 15 times the highest recorded number of fledges recorded in the history of the database for this region. The sites with the most years active were Carlos Pointe and Second Chance (9 years) and the site with the least years active was Ten Thousand Islands (1 year; Table 17, in Appendix C).

700

600

500

400

300

200 Black Skimmer Black Skimmer nests y = 0.0653x + 41.132 R² = 0.0075 100

0 0 100 200 300 400 500 600 Least Tern nests

Black Skimmer Least Tern nests nests Black Skimmer nests 1 Least Tern nests 0.086368 1

Figure 4: Relationship between number of Least Tern and Black Skimmer nests in Southwest Florida from 2011-2019. There was no correlation between the two species (r2 = 0.007).

120

100 P=0.255661 80 y = -3.0204x + 6154.5 R² = 0.1796 60

40 Mean Least Tern Nests

0 2008 2010 2012 2014 2016 2018 2020 2022 Year

Figure 5. Linear regression analysis of mean number of Least Tern nests surveyed in 16 southwest Florida colonies during 2011-2019. P=0.255661.

250

P= 0.025169 200 y = 14.946x - 30013 R² = 0.5348

150

100

MeanBlack Skimmer Nests 50

0 2008 2010 2012 2014 2016 2018 2020 2022 Year

Figure 6. Linear regression analysis of mean number of Black Skimmer nests surveyed in 16 southwest Florida colonies during 2011-2019. P=0.025169.

Survey counts were analyzed to determine whether the number of fledged Least Terns varied significantly with respect to year. The data did not meet the assumptions of normality required for analysis of variance, ANOVA, and could not be transformed to meet the assumptions. Therefore, a nonparametric Kruskal-Wallis test was performed.

The Kruskal-Wallis test indicated that there were significant differences in the number of

Black Skimmer fledglings in at least two of the surveyed years (P=0.0043; Table 3a). The results of the Wilcoxon/Mann-Whitney U nonparametric analysis indicated that there was not a significant difference in the number of fledged Black Skimmers between Lee and Collier

(P=0.0548; Table 3b).

The Kruskal-Wallis test indicated that there was a significant difference in Least Tern fledglings between at least two of the surveyed years (P<0.0001; Table 4a). The results of the

Wilcoxon/Mann-Whitney U nonparametric analysis indicated that there was a significant difference in the number of fledged Least Terns between the two counties (P=0.0011; Table 4b).

A multiple comparisons Steel Dwass test was done, and showed that only 2012 and 2018 were statistically different from each other in the number of fledged Black Skimmers (P=0.0319;

Table 5). A Steel-Dwass multiple comparisons test indicated that, for Least Terns, years 2015 and 2016, 2012 and 2016, 2018 and 2014, and 2018 and 2017 had significant differences in the number of fledges between them (Table 6).

Productivity Estimates

The calculated productivity estimates when dividing the number of fledged chicks by the number of nests per year for Least Terns are as follows: 2011- 0.18, 2012- 0.17, 2013- 0.42,

2014- 0.26, 2015-0.16, 2016-0.21, 2017-0.43, 2018-0.11, 2019- 0.54 (Table 9). 44

The calculated productivity estimates when dividing the number of fledged chicks by the number of nests per year for Black Skimmers are as follows: 2011- 1.05, 2012- 0, 2013- 0.72,

2014- 0.19, 2015- 0, 2016- 0.52, 2017-0.34, 2018- 0.51, 2019- 0.57 (Table 12).

Table 3. Black Skimmer Wilcoxon/Kruskal-Wallis Tests (Rank Sums) for year (a) and county (b). The results of the Wilcoxon/Mann-Whitney U nonparametric analysis indicated that there was not a significant difference between Lee and Collier (P=0.0548). The Kruskal-Wallis test indicated that there were significant differences in the number of Black Skimmer fledglings in at least two of the surveyed years (P=0.0043). a.)

Year Count Score Sum Expected Score Mean (Mean- Score Mean0)/Std0 2011 27 7091.00 7722.00 262.630 -1.099 2012 28 6482.00 8008.00 231.500 -2.613 2013 51 14213.5 14586.0 278.696 -0.482 2014 40 10428.0 11440.0 260.700 -1.446 2015 33 8471.50 9438.00 256.712 -1.531 2016 137 40848.0 39182.0 298.161 1.443 2017 104 28772.5 29744.0 276.659 -0.931 2018 104 32797.5 29744.0 315.361 2.926 2019 47 14202.0 13442.0 302.170 1.022

1-Way Test, ChiSquare Approximation ChiSquare DF Prob>ChiSq 22.3284 8 0.0043 b.)

Level Count Score Sum Expected Score Mean (Mean- Score Mean0)/Std0 Collier 437 127183 124982 291.037 1.921 Lee 134 36123.0 38324.0 269.575 -1.921

2-Sample Test, Normal Approximation S Z Prob>Z 3.6123 -1.92056 0.0548

1-Way Test, ChiSquare Approximation ChiSquare DF Prob>ChiSq 3.6902 1 0.0547

Table 4. Least Tern Kruskal-Wallis Tests (Rank Sums) for year (a) and county (b). The Kruskal- Wallis test indicated that there was a significant difference in Least Tern fledglings between at least two of the surveyed years (P<0.0001). The results of the Wilcoxon/Mann-Whitney U nonparametric analysis indicated that there was a significant difference in the number of fledged Least Terns between the two counties (P=0.0011). a.)

Year Count Score Sum Expected Score Mean (Mean- Score Mean0)/Std0 2011 36 105243.0 12078.0 292.306 -1.459 2012 42 10027.0 14091.0 238.738 -3.548 2013 100 39813.0 33550.0 398.130 3.720 2014 82 30677.0 27511.0 374.110 2.044 2015 61 15285.5 20465.5 250.582 -3.811 2016 155 52535.5 52002.5 338.939 0.267 2017 72 28182.5 24156.0 391.424 2.751 2018 67 18811.5 22478.5 280.769 -2.587 2019 55 18930.0 18452.5 344.182 0.368

1-Way Test, ChiSquare Approximation ChiSquare DF Prob>ChiSq 55.4190 8 <0.0001 b.)

Level Count Score Sum Expected Score Mean (Mean- Score Mean0)/Std0 Collier 363 114092 121787 314.302 -3.268 Lee 307 110694 102999 360.565 3.268

2-Sample Test, Normal Approximation S Z Prob>Z 110693.5 3.26840 0.0011*

1-Way Test, ChiSquare Approximation ChiSquare DF Prob>ChiSq 10.6838 1 0.0011*

Table 5. Nonparametric Comparisons For All Pairs Using Steel-Dwass Method for Black Skimmer fledglings between years (2011-2019). Only 2012 and 2018 were statistically different from each other in the number of fledged Black Skimmers.

Level -Level Score Mean Std Err Diff Z p-Value Difference 2018 2012 19.6504 6.050586 3.24769 0.0319

q* Alpha 3.10173 0.05

Table 6. Nonparametric Comparisons For All Pairs Using Steel-Dwass Method for Least Tern fledglings between years (2011-2019). Years 2015 and 2016, 2012 and 2016, 2018 and 2014, and 2018 and 2017 had significant differences in the number of fledges between them.

Level -Level Score Mean Difference Std Err Diff Z p-Value 2013 2012 32.3726 7.189732 4.50262 0.0002 2016 2015 30.0869 8.778034 3.42753 0.0177 2016 2012 30.0039 9.179037 3.26874 0.0299 2017 2015 25.9217 6.218794 4.16828 0.0010 2014 2012 25.0232 6.373724 3.92600 0.0028 2017 2012 22.8829 5.905212 3.87504 0.0034 2018 2014 -21.5608 6.721995 -3.20750 0.0362 2018 2017 -22.1294 6.402731 -3.45624 0.0160 2015 2014 -28.2312 6.574458 -4.29407 0.0006 2018 2013 -29.4992 7.304950 -4.03825 0.0018 2015 2013 -35.4464 7.207312 -4.91812 <0.0001

q* Alpha 3.10173 0.05

Discussion

Methodological Considerations

Declines in the reproductive success of beach-nesting birds may result from predation, intense weather events such as cyclonic storms, and tides/flooding (Burger et al., 1994). Any of these factors may cause total failure of a breeding colony. Failure can result in either colony abandonment or massive re-nesting (Burger & Gochfeld, 1991). Anthropogenic causes of reproductive losses include direct disturbance such as walking in colonies, off-road vehicles, dogs, habitat loss, and pollutants (Peakali, 1992; Shope, 2020).

Algal blooms have the potential to poison shorebirds through direct ingestion, or bioaccumulation in filter-feeding invertebrate prey (Gibble & Hoover, 2018). While it is believed that seabirds accumulate toxins through the ingestion of affected prey, they have also been shown to be susceptible to the nontoxic byproducts of algal blooms such as surfactants that foul their feathers and decrease their waterproofing capacity, which has resulted in mortality events.

Climate warming and eutrophication has led to the increase in severity, frequency, intensity, and composition of these harmful blooms (Gibble & Hoover, 2018). Understanding the relationship between harmful algal blooms and seabird mortality is crucial for the effective monitoring and management of future populations and may also have broader implications for the health of local marine environments (Gibble & Hoover, 2018). Black Skimmers had a combined fledged count of 523 for both counties in 2018, but Least Terns only had 92 fledged chicks during that year.

2018 was a year in which Florida suffered from a particularly menacing red tide event that ravaged the Southwest Florida coast. What may have been an extremely threatening occurrence for Least Terns seems not have affected Black Skimmer populations as dramatically. As 49 populations of shorebirds are studied more thoroughly, it is important to pay attention to the catastrophic effects that red tide may have on them.

Coastal colonial species have evolved alongside the natural forces of storms, tides, and natural predators, so their populations have a history of withstanding them. (Burger & Gochfeld,

1990a). However, the synergy of additional pressures of increased predator abundance, human disturbance, and pollutants may diminish reproductive success to levels that are not sustainable

(Burger, 1994).

In any given year, it is possible to have events occur which lead to varied productivity in a colony. In this case, the years that showed higher nest or egg counts than fledged counts may have been as a result of a wash out event or spike in predation.

Also notable, for Black Skimmers, recorded productivity was zero in 2012. While this could be attributed to something like a catastrophic environmental event that would wipe out the fledglings in a colony, what likely occurred in that year was simply a lack of resources to survey birds. In 2012, the FSD was still considerably young, and it is probable that many sites were not being monitored as frequently or as diligently as they are now.

Of the 16 sites, Big Marco Pass had the most nests, fledglings, and adult birds of both species. What is interesting here is that the highest number of total adults counted was roughly fifteen times that of the total fledged. This was likely due to the fact that not all adult birds are able to breed and may utilize sites for food or other resources.

Consequences of varying rates of reproductive success within the region include: potential population decreases in the future in some areas versus increases in other areas; steady regional populations with some sites contributing recruitment to other sites that have lower reproductive success; abandonment of sites with low reproductive success; and merging of 50 colonies into sites with high reproductive success (Burger, 1994). Patterns in monitoring data will indicate reproductive impairment and population trends and can also indicate areas where further study is warranted (Burger, 1994).

One other consequence of low productivity is colony desertion and subsequent immigration to other, more productive colonies. Burger (1982) indicated that Black Skimmers do change sites when reproductive success has diminished. If shifts such as these continue, regional populations may merge into few, bigger colonies located on more secure nesting sites (Burger,

1994). This potential loss of spatial variability on the landscape is disadvantageous because it increases the risk of devastating events affecting a sizeable amount of the population (Burger,

1994).

In Collier county, Black Skimmer numbers have diminished in some years but have remained stable in the past two years or so, with fledged counts being in the 400s (Table 10).

However, Lee county Black Skimmers have not been so productive. Lee county Black Skimmer fledglings peaked in 2018 at 112 chicks, but were not nearly as successful in 2019, with the peak number of fledglings only reaching 33 (Table 11). The pattern has shown that Lee sites have not been as productive for both Black Skimmers and Least Terns as Collier sites have. This may be attributed to the fact that there are simply more nesting sites in Collier than there are in Lee.

What is of particular interest is that, although Least Terns have had more nests than Black

Skimmers, Black Skimmers have shown to have higher numbers of fledged chicks (Tables 9 &

12). Perhaps Least Tern chicks have a higher mortality rate than Black Skimmer chicks, causing tern chicks to not live to fledging age. Perhaps being that Black Skimmers are naturally a larger and more robust bird, they are less susceptible to predation than the smaller Least Terns. 51

Census work that is conducted over a large geographical region and time period is subject to several potential biases, including selection of colonies to monitor, methods of determining reproductive success, and observer bias. This study aimed to minimize those confounding factors. The data in the FSD is collected by members of the FSA who do counts by observing birds in the field during specified count windows. Observer bias can occur if there is a lack of agreement between observer estimates of the number of birds, or if an observer consistently over- or under-estimates the number of fledglings or adults (Burger et al., 1994). To reduce this source of error, observers are trained with the same field protocol, and total counts are conducted at least twice, then averaged, in order to get a more accurate estimate. Reproductive success may be underestimated, when some fledglings leave the colony undetected between counts or are not present during a count. However, Least Terns and Black Skimmers nest on open beaches with high visibility, and the number of nesting pairs and fledged young can be accurately counted with patience (Burger et al., 1994), making these factors less likely. Also noteworthy is that, although beneficial for spatial analyses of colony presence, estimate counts do not provide as reliable data as direct counts do. Years 2015-2019 consisted of more direct count data, so these years may provide a more accurate representation of population dynamics.

The selection of colonies to monitor is potentially flawed if colonies selected are not representative of the entire population (Burger et al., 1994) or not consistently monitored annually. Possible biases may also occur where only large, stable colonies are monitored and smaller, transitory colonies are overlooked (Burger et al., 1994). Consequently, this study was designed to include all surveyed colonies in Lee and Collier counties along the Gulf of Mexico coast of Florida. 52

That aside, it is important to note that there may be sites along the Florida Gulf Coast in which seabird nesting is occurring that are not actively being surveyed due to a variety of reasons. The FSA estimates that, in 2019, there were 2,274 pairs of ground nesting Black

Skimmers in the Southwest Florida region, which is significantly more than any other region in the state (FWC, 2020). About 77% of Black Skimmers that breed in Florida have been documented in Southwest colonies (FWC, 2020).

One reason to monitor all colony sites within a study area is that beach-nesting birds change colony sites when shoreline erosion occurs as a result of storms or tides (Burger et al.,

1994). Still, Least Terns do often nest in the same general area annually (Burger, 1984; Atwood

& Massey, 1988). The possibility of major colony shifts makes it challenging to select a sampling regimen prior to nesting initiation. Thus, by sampling all known colonies of Least

Terns and Black Skimmers, the need to select was eliminated, rendering it possible to make an estimate of the entire populations for each species (Burger et al., 1994).

Hurricanes are ecologiucally transformative and may create favorable habitat for beach nesting birds. The relationships between seabirds/shorebirds and storms are complex. Storms that are too frequent may cause recruitment into the breeding population to not be enough to account for adult loss and sustainance of the population (FWC, 2020). On the other hand, if storms are not frequent enough, natural dune succession and vegetation reduces the availability of potential nesting habitat, elevates predation rates, and diminishes productivity (FWC, 2020). Hurricane

Irma hit the southwest coast of Florida during September of 2017. During that year, a shift in the number of nests from bnoth species occurred. Particularly in Lee County, both species experienced declines in nest counts. It may be considered that the hurricane was a catalyst for this reaction, but cannot be gathered from the data. 53

Implications for management

Future studies on imperiled beach nesting birds should consider the following factors.

Return rates

Although some breeding sites are temporary, many are used in repeated years.

Research on site fidelity is vital to long-term protection of active breeding sites (FWC,

2013). Colony fidelity for banded Least Tern adults has been documented throughout their breeding range (Atwood & Massey, 1988, Renken & Smith, 1995). Research is necessary to measure the return rate of breeding adults to their natal colony sites, in order to approximate evident survival and recruitment of Florida-reared chicks (FWC, 2013).

Reproductive success

Estimates of reproductive success are needed to define long-term population trends, the relative importance of nesting sites or colonies, and if sub-populations are replacing themselves or are relying on other populations for recruitment (Burger et al. 1994). Research should also focus on exploring factors that limit chick and fledgling survival.

Juvenile rates of survival and dispersal

To predict the viability of avian populations, it is critical to understand juvenile survival and dispersal rates (Stenzel et al. 2007). A statewide banding program focused on juvenile imperiled beach nesting birds would supplement this research (FWC, 2013). This program would use capture-recapture procedures, where birds are marked distinctively with bands or flags and then re-released into the population where they can be re-sighted

(Williams et al. 2002).

Banding birds makes long term population studies more feasible, and it provides information on the dispersal and migration of different species (Weimerskirch et al., 1985). 54

Combined with the efforts of programs such as MOTUS and eBird, banding can be an incredibly effective way to learn about bird migration patterns. The process involves placing an aluminum ring around a bird’s leg; the band bears a number that allows for the bird to be easily identified if it is found again (Samsonenko, 2000). Banding also allows for birds to be studied as individuals. The wealth of data generated is also useful for studying population biology and productivity (Samsonenko, 2000). For future studies on seabird population dynamics, banding is fundamental. Without it, the behavior and ecology of these birds cannot be fully understood. It is notable that, banding Least Tern and Black Skimmer chicks in the region where my study was done would also allow for more in-depth study and for the following of individuals via recapture methods. Black Skimmer banding began in 2015 in Pinellas County,

Florida and 2017 at Sand Dollar Island (Collier County). In 2018, Marco Island’s Beach and

Coastal Resources Advisory Committee partnered with Audubon of the Western Everglades to continue Black Skimmer banding.

Managing Critical Habitat

Acute events such as hurricanes can dramatically alter ecosystems. Coastal erosion and storm surges have the potential to drastically change or even destroy critical shorebird habitat, and the spatially extent of these storms can result in negatively impacted colonies over an entire region.. However, issues that gradually increase in intensity also have the potential to threaten these ecosystems. The effects of anthropogenic global climate change will manifest through changes in land usage, prey availability, mismatching of arrival dates and prey dynamics, predation effects, disease, and parasitism (Sutherland et al., 2012). The complexity of these interactions will make it difficult to predict the response of shorebird species. Given this, it will become increasingly important to conserve and manage habitats that are known to be significant 55 in the seabird life cycle. Further, as a consequence of thermal expansion, average sea level is predicted to rise faster than ever observed (Sutherland et al., 2012). The loss of ice has broadened the expanse of near-shore open water, providing greater fetch for waves and altering shorebird nesting and littoral feeding habitats (Sutherland et al., 2012). Man-made structures to prevent flooding are likely to impede the relocation of intertidal habitats.

The results of this study show Big Marco Pass to be a critically important site for both

Black Skimmers and Least Terns. It is crucial that sites such as Big Marco Pass be protected for the purpose of conserving coastal birds in the state, to safeguard regional populations in this part of the world. These already threatened species are particularly vulnerable when relying so heavily on few sites to breed. Random stochastic events such as hurricanes could have serious consequences for productivity. Migratory species such as the Least Tern and Black Skimmer differ from others because they depend on multiple locations that may be spread over continents, and individual sites may support substantial proportions of whole populations during the course of annual migrations (Sutherland et al., 2012). Migrants inhabit not only breeding and nonbreeding sites, but also a range of migratory routes and stopover locations in between

(Faaborg et al., 2010; Bayly et al., 2018). The loss of any of these key sites at any point along migratory routes can therefore have far-reaching consequences for entire populations (Sutherland et al., 2012). Management decisions are informed by identifying site-specific factors that limit reproduction and site fidelity (FWC, 2013). Documenting distribution and recognizing the factors that trigger movement patterns are critical to the recovery of Black Skimmer and

Least Tern populations (FWC, 2013). There is a demonstrated need for strengthened resources to study migratory species in areas like Florida that are proven to be crucial for migratory species

(Lefevre & Smith, 2020). The monitoring of species’ movements with a collaborative approach 56 can lead to more efficient use of resources and more effective conservation action (Lefevre &

Smith, 2020).

Recommendations for Future Research

It is important that any future studies conducted using similar methods to this one take into account the critical need for streamlining data entry and data management. Prioritizing an organized method for data entry on the observer end will make forthcoming analyses more straightforward. Additionally, when analyzing the data, it is equally important to make the method of data sorting easier. Having thousands of data entries will make it difficult to gather meaningful results unless it is compiled in a systematic way.

Closing Notes

As development continues to expand along coastal areas, it is critical that large, ecologically important nesting sites be constantly monitored and maintained. Further, management decisions must be informed by population studies, in order to assure that conservation efforts are maximized. Monitoring is crucial in order to measure the success of management plans and conservation objectives. Data collection in large quantities should be coordinated efficiently in order to streamline future research efforts. Data should be collected with the research objectives in mind so the process of analysis is simplified.

The purpose of this study was to highlight the dynamics between the populations of these seabirds in a region that is critically important to their breeding biology. Each nesting season has presented unique challenges for both Least Terns and Black Skimmers, which has offered opportunities for monitors to learn about their reproductive ecology and how to develop conservation efforts. The monumental effort by the FSA has allowed for the use of data in the 57

FSD to lend insight to population estimates in the state, which will bolster protection of our remarkable coastal wildlife.

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APPENDIX A

Peak Counts and Productivity Estimates

Table 7. Peak Least Tern nest, fledged, and adult counts for Collier County.

Year Peak Nests Peak Fledged Peak Adults 2011 837 172 183 2012 757 37 1430 2013 892 203 702 2014 761 130 700 2015 358 5 1161 2016 661 213 1544 2017 635 341 1216 2018 623 7 1309 2019 184 40 444

Table 8. Peak Least Tern nest, fledged, and adult counts for Lee County.

Year Peak Nests Peak Fledged Peak Adults 2011 264 26 524 2012 295 144 539 2013 188 251 732 2014 285 144 546 2015 306 103 580 2016 515 39 419 2017 256 45 641 2018 246 85 446 2019 366 259 779

Table 9. Total peak number of Least Tern nests, fledglings, and adults for both Lee and Collier counties combined. Productivity estimates done by dividing number of fledged birds by number of nests.

Productivity Peak Nests Peak Fledged Peak Adults Year Estimate Total Total Total (fledged/nests) 2011 1101 198 707 0.179837 2012 1052 181 1969 0.172053 2013 1080 454 1434 0.42037 2014 1046 274 1246 0.26195 2015 664 108 1741 0.162651 2016 1176 252 1963 0.214286 2017 891 386 1857 0.433221 2018 869 92 1755 0.105869 2019 550 299 1223 0.543636

Table 10. Peak Black Skimmer nest, fledged, and adult counts for Collier County.

Year Peak Nests Peak Fledged Peak Adults 2011 287 349 2257 2012 139 0 1405 2013 628 502 1386 2014 677 158 739 2015 195 0 1174 2016 587 536 1825 2017 784 331 1874 2018 690 411 2522 2019 493 464 1170

Table 11. Peak Black Skimmer nest, fledged, and adult counts for Lee County.

Year Peak Nests Peak Fledged Peak Adults 2011 44 0 44 2012 118 0 118 2013 72 0 72 2014 208 14 208 2015 425 56 425 2016 450 1 450 2017 195 2 195 2018 329 112 329 2019 375 33 375

Table 12. Total peak number of Black Skimmer nests, fledglings, and adults for both Lee and Collier counties combined. Productivity estimates done by dividing number of fledged birds by number of nests.

Productivity Peak Nests Year Peak Fledged Total Peak Adults Total Estimate Total (fledged/nests) 2011 331 349 2301 1.054381 2012 257 0 1523 0 2013 700 502 1458 0.717143 2014 885 172 947 0.19435 2015 620 1 1599 0.001613 2016 1037 537 2275 0.51784 2017 979 333 2069 0.340143 2018 1019 523 2851 0.513248 2019 868 497 1545 0.572581

APPENDIX B

Nest Counts and Count Windows

Table 13. Least Tern nest count windows by week beginning at initiation date for each year. Nest counts include all nests from all sites within the count window. Peak counts for each year inbold.

2011 2012 2013 2014 2015 2016 2017 2018 2019

WEEK 1 805 713 557 291 527 816 698 3 414 WEEK 2 0 0 593 95 114 0 101 0 2 WEEK 3 0 1 300 47 9 152 42 0 1 WEEK 4 18 0 42 124 0 0 0 48 23 WEEK 5 191 58 5 0 0 0 0 200 0 WEEK 6 29 0 0 0 0 0 0 20 107 WEEK 7 41 0 0 0 0 0 6 5 3 WEEK 8 0 0 0 0 0 0 0 254 0 WEEK 9 0 0 12 0 0 0 0 15 0 WEEK 10 0 0 0 0 0 0 0 2 0 WEEK 11 0 0 0 2 0 0 0 4 0 FIRST DATE OF PEAK 4/19 4/17 4/30 4/20 4/24 4/24 4/24 5/25 4/25 WINDOW DAY OF YEAR # 109 108 120 110 114 115 114 145 109

Table 14. Black Skimmer nest count windows by week beginning at initiation date for each year. Nest counts include all nests from all sites within the count window. Peak counts for each year in bold.

2011 2012 2013 2014 2015 2016 2017 2018 2019 Week 1 287 138 550 677 326 109 744 369 493 Week 2 0 0 0 30 0 461 0 410 57 Week 3 0 5 30 0 0 0 40 0 0 Week 4 0 0 48 0 0 91 41 0 0 Week 5 0 0 15 0 0 0 0 0 0 Week 6 0 0 0 0 0 31 0 0 0 First date of peak 5/17 5/23 5/15 5/28 5/14 5/24 5/15 5/23 5/18 window Day of year # 137 144 135 148 134 145 135 143 138

Table 15. Total number of Least Tern nests (all sites included) by the first date of each count window. Year First date of peak Day of year Number of nests window (n) 2011 4/19/11 109 805 2012 4/17/12 108 713 2013 4/30/13 120 593 2014 4/20/14 110 291 2015 4/24/15 114 527 2016 4/24/16 115 816 2017 4/24/17 114 698 2018 5/25/18 145 254 2019 4/25/19 115 415

Table 16. Total number of Black Skimmer nests (all sites included) by the first date of each count window. Year First date of peak Day of year Number of nests window (n) 2011 5/17/11 137 287 2012 5/23/12 144 138 2013 5/15/13 135 550 2014 5/28/14 148 677 2015 5/14/15 134 326 2016 5/24/16 145 461 2017 5/15/17 135 744 2018 5/23/18 143 410 2019 5/18/19 138 493

APPENDIX C

Colony Site Statistics

Table 17. Total Black Skimmer and Least Tern nests, fledged, and adults per site (all years added together) with number of years each site was active. Site Name County Total Nests Total Total Adults # Years Fledged Active

Big Hickory Lee 78 17 328 2 Big Marco Collier 58164 11605 185053 8 Pass Bowditch Lee 90 420 969 1 Captiva Lee 471 264 1450 5 Carlos Lee 13484 3412 35318 9 Pointe Caxambas Collier 873 256 3660 4 Cayo Costa Lee 96 2 605 6 Gasparilla Lee 331 33 915 5 Keewaydin Collier 2329 320 8609 8 Kice Island Collier 20 3 122 1 Lovers Key Lee 480 6 447 4 Morgan Collier 128 5 346 2 Beach New Beach Collier 105 4 203 1 Sanibel Lee 101 11 266 4 Second Collier 8005 1019 22872 9 Chance Ten Collier 2 0 12 1 Thousand Islands

APPENDIX D

Nest Counts by Day of Year

Figure 7. Least Tern and Black Skimmer nest counts by nth day of the year. Least Terns begin nesting earlier in the year, with Black Skimmers to follow a few weeks later.

73 a).

700

600

500

400

300

200 Peak Least Tern Nests Tern Least Peak

100

0 0 50 100 150 200 250 Lee Collier nth Day of the Year

b).

600

500

400

300

200

Peak Black Nests Black Skimmer Peak 100

0 0 50 100 150 200 250 Lee Collier nth Day of the Year

Figure 8. Peak Least Tern nests on the nth day of the year by county (a) and Peak Black Skimmer nests on the nth day of the year by county (b). Highest nest counts for each species taken from each of the 16 study sites and added together for years 2011-2019. 74

APPENDIX E

Nest, Fledged, and Adult Counts for Lee and Collier County

Figure 9. Peak nest counts combined for all sites in Lee county (orange) and Collier County (blue) for Black Skimmers and Least Terns. Highest nest counts for each species taken from each of the 16 study sites and added together for years 2011-2019.

Figure 10. Peak fledged counts combined for all sites in Lee county (orange) and Collier County (blue) for Black Skimmers and Least Terns. Highest fledged chick counts for each species taken from each of the 16 study sites and added together for years.

Figure 11. Peak adult counts combined for all sites in Lee county (orange) and Collier County (blue) for Black Skimmers and Least Terns. Highest adult counts for each species taken from each of the 16 study sites and added together for years 2011-2019.

Figure 12. Peak total nest counts for Black Skimmers and Least Terns. Nest counts for both Lee and Collier counties added together for each species.

Figure 13. Peak total fledgling counts for Black Skimmers and Least Terns. Fledged counts for both Lee and Collier counties added together for each species.

Figure 14. Peak total adult counts for Black Skimmers and Least Terns. Adult counts for both Lee and Collier counties added together for each species.