Abstract Species Composition, Relative

ABSTRACT

SPECIES COMPOSITION, RELATIVE ABUNDANCE, AND HABITAT OCCURRENCE OF NEOTROPICAL MIGRATORY BIRDS OVERWINTERING IN DOMINICA, WEST INDIES

by Heather N. Roades

With declines in the populations of many Neotropical migratory birds, it is increasingly necessary to understand their complete life cycle specifically during the overwintering period. Research on overwintering Neotropical migrants is sparse for the Lesser Antilles including the island of Dominica. Species composition, relative abundance, and habitat occurrence of Neotropical migratory birds overwintering in two habitats in Dominica was documented during December 2008 and January 2009. Mist-nets were used to determine species composition and relative abundance. Migrants were only detected at one location, Cabrits National Park. Two species of Neotropical migrants were captured, American Redstart (Setophaga ruticilla) and Northern Waterthrush (Parkesia noveboracensis), accounting for 8% of the total birds captured. This research provides a base-line for future study of Neotropical migrants in Dominica and highlights Dominica’s conservation potential.

SPECIES COMPOSITION, RELATIVE ABUNDANCE, AND HABITAT OCCURRENCE OF NEOTROPICAL MIGRATORY BIRDS OVERWINTERING IN DOMINICA, WEST INDIES

A Thesis

Submitted to the

Faculty of Miami University

in partial fulfillment of

the requirements for the degree of

Master of Arts

Department of Geography

Heather Nicole Roades

Miami University

Oxford, Ohio

2012

Advisor______Dr. William H. Renwick

Reader______Dr. David E. Russell

Reader______Ms. Robbyn J. F. Abbitt Table of Contents

List of Tables ...... iii

List of Figures ...... iv

Acknowledgements ...... v

Chapter 1. INTRODUCTION ...... 1 Chapter 2. LITERATURE REVIEW ...... 3 What is a Neotropical Migratory Bird? ...... 3 Migration...... 3 Evidence of Population Declines ...... 5 Research Needs ...... 7 Neotropical Migratory Birds in the Caribbean ...... 8 American Redstart ...... 9 Northern Waterthrush ...... 10 Resident Species of Dominica ...... 11 New Ways to Study Migratory Birds...... 11 Chapter 3. METHODS...... 13 Research Location ...... 13 Research Sites ...... 14 Cabrits National Park ...... 15 Archbold Tropical Research and Education Center (ATREC) ...... 18 Mist-netting and Banding ...... 20 Chapter 4. RESULTS...... 21 Cabrits National Park ...... 22 Migrants Captured at Cabrits ...... 22 Residents Captured at Cabrits ...... 23 Archbold Tropical Research and Education Center (ATREC) ...... 23 Migrants Captured at ATREC ...... 24

Residents Captured at ATREC ...... 24 Chapter 5. DISCUSSION ...... 28 Migrants in Dominica ...... 28 American Redstart ...... 29 Northern Waterthrush ...... 30 Residents of Dominica ...... 31 Research Limitations ...... 32 Future Research ...... 33 Conservation ...... 33 Conclusions ...... 36 REFERENCES ...... 37

iii

List of Tables

Table 1. Banding dates and number of banding days by location ...... 20

Table 2. Total birds banded by species and location ...... 21

Table 3. Total birds captured by species and location ...... 22

Table 4. Neotropical migrant species and number of individuals captured at Cabrits National Park ...... 23

Table 5. Resident species and number of individuals captured at Cabrits National Park ...... 23

Table 6. Resident species and number of individuals captured at ATREC ...... 24

Table 7. Species captured only at Cabrits National Park ...... 25

Table 8. Species captured only at ATREC ...... 25

Table 9. Species codes for captured species ...... 25

Table 10. Relative abundance by species and location ...... 27

List of Figures

Figure 1. “Connectivity between breeding and wintering populations of Black-throated Blue Warblers, as indicated by analyses of stable isotope values in feathers (Rubenstein et al. 2002). The pattern suggests that individuals from the northern portion of the breeding range migrate to and winter in the western Greater Antilles (mainly Cuba and Jamaica), while those breeding in the more southern Appalachian Mountains winter mostly in the more easterly Antilles (Hispaniola, Puerto Rico). Results from Rubenstein et al. (2002).” (From Holmes 2007. Based on Rubenstein et al. 2002) ...... 4

Figure 2. “Thirty-seven-year trend in numbers of breeding birds occupying a 10-ha study area in northern hardwood forest at Hubbard Brook, New Hampshire, USA, 1969-2005. Numbers are totals for all species (males plus females) for permanent residents, short- distance migrants, long-distance (Neotropical) migrants and all species combined.”(From Holmes 2007) ...... 5

Figure 3. Cerulean Warbler (Setophaga cerulea), BBS Trend Map, 1966 – 2003 (From Sauer et al. 2008) ...... 6

Figure 4. Prairie Warbler (Setophaga discolor) BBS Trend Map, 1966 – 2003 (From Sauer et al. 2008) ...... 6

Figure 5. American Redstart (Setophaga ruticilla), ASY male. Photo by H. Roades ...... 9

Figure 6. Northern Waterthrush (Parkesia noveboracensis). Photo by H. Roades ...... 10

Figure 7. The Caribbean with Dominica highlighted ...... 12

Figure 8. The Lesser Antilles. Puerto Rico is not part of the Lesser Antilles ...... 13

Figure 9. Location of the research sites within Dominica ...... 14

Figure 10. Cabrits National Park research site. The circle outlines the extent of The Swamp and the line illustrates the location of the trail used as a net lane ...... 15

Figure 11. Cabrits research site from across Prince Rupert Bay. The arrow represents the location of the net lane trail bisecting the peninsula. The Swamp is located to the right of the arrow. Note the dramatic difference in elevation on each side of the research site. Photo by H. Roades ...... 16

Figure 12. Habitat types on each side of the research site at Cabrits National Park. On the left: dry-scrub forest. On the right: The Swamp with mangroves in the foreground. Photos by H. Roades ...... 17

Figure 13. Location of research site at Archbold Tropical Research and Education Center (ATREC). The Bee Cottage was used a banding station ...... 18

Figure 14. Secondary rainforest along an old estate road used as a net lane at ATREC. Photo by H. Roades ...... 19

Figure 15. Relative abundance for all species captured at Cabrits National Park. Neotropical migrants in bold. See table 9 for species codes ...... 26

Figure 16. Relative abundance for all species captured at ATREC. See table 9 for species codes ...... 26

Figure 17. American Redstarts captured at Cabrits National Park. On left: SY sex unknown. Center: SY male. Right: ASY male. Photos by H. Roades ...... 30

Figure 18. Northern Waterthrushes captured at Cabrits National Park. Sexes unknown. Photos by H. Roades ...... 30

Figure 19. Bananaquit. Left: individual with white supercilium. Right: individual with yellow and white supercilium and grey on crown. Photos by H. Roades...... 31

Figure 20. Plumbeous Warblers. On left: adult. On right: juvenile. Photos by H. Roades ...... 32

Figure 21. Protected lands within Dominica (from Dominica 2000) ...... 35

Acknowledgements

Thanks need to be given to the Department of Geography for providing research funding and a “home” at Miami University. I would also like to thank the Hefner Zoology Museum for giving me the opportunity to work in such a wonderful place.

Thanks to the Forestry, Wildlife, and Parks Division of Dominica for permitting my research and Arlington James in particular for his insight and suggestions. I am indebted to Neil Winn for his help during my research, without which I could not have succeeded.

Finally, I would like to express my gratitude to the members of my committee: Bill Renwick, Dave Russell and Robbyn Abbitt. Thanks for the time, effort, and endless support.

vii

Chapter 1

INTRODUCTION

The Commonwealth of Dominica, an island nation located within the Lesser Antilles, is potentially an important over-wintering location for Neotropical migratory birds. This is due in part to its abundant natural vegetation1 (~65%), which has earned it the name “The Nature Island of the Caribbean” (Dominica 2001). Dominica has a significant amount of primary forest that accounts for 36% of the total land area of the island, more than any other island in the Caribbean (FAO 2008). Widespread deforestation and habitat destruction throughout much of the Caribbean has left Dominica as a habitat “island” amid widespread environmental change. As a relatively large, undisturbed habitat patch Dominica has a potentially important role in future conservation efforts for the entire region.

To date, no published quantitative research on the distribution and abundances of Neotropical migratory birds has been conducted in Dominica. Bird identification guides are available for Dominica and the West Indies, but most of the information on Neotropical migrants is the result of casual observations not systematic surveys (James et al. 2005, Raffaele et al. 2003). As a result, many species are likely underrepresented in the species lists and counts for the island. Consequently, it is necessary to ascertain Dominica’s current importance to Neotropical migrants to better plan local, regional, or global conservation efforts.

In light of the above points, the objective of this research was to do the following in Dominica:

 Determine the species composition2 of migrant birds within a secondary wet forest and a dry scrub forest/mangrove swamp.  Determine the relative abundance2 of migrant bird species within secondary wet forest and a dry scrub forest/mangrove swamp.  Determine the habitat occurrence for migrant species.

This research contributes to an understanding of the species composition, relative abundance and habitat occurrence of Neotropical migrants over-wintering in secondary and dry scrub forests in Dominica. Research that provides base-line data will be essential in the development of long- term research projects critical to Neotropical migrant conservation and aid in the planning for local developments in Dominica.

1 This includes: forest, swamp, savannah/grassland, and any other naturally occurring habitats. 2 Species composition refers to the number of different species that are present in a given area. Relative abundance is a measure of the number of each species that is present in a given area divided by the total number of species in that location. Habitat occurrence refers to each individual species and the habitats in which they occur. For example, if Northern Waterthrushes occur in two different forest types, mangrove and coastal scrub, but are encountered more often in mangroves than the coastal scrub N. Waterthrushes have a greater rate of occurrence within mangroves. This is an important distinction, especially when determining the preferred habitat(s) for each species. Comparisons of species composition and relative abundance were made between the two habitat types.

There are many gaps in our knowledge regarding the ecology of Neotropical migratory birds. In the search for answers to the causes for the declines of Neotropical migratory birds many basic questions remain to be answered. Such critical questions include:

1. What is the driving factor behind declines in Neotropical migratory bird populations? 2. What are the precise wintering ranges and migratory pathways of migrant species? 3. How important are individual locations? 4. What are the habitat requirements for overwintering migrants? 5. What are the food preferences for overwintering migrants?

This is particularly true for overwintering migrants in Dominica. This research contributes to the knowledge of the wintering ecology of Neotropical migrants by establishing some baseline data on the birds that spend their winters on Dominica. Understanding where and how these birds spend their winters in an integral piece of the puzzle, but it is just one part of the effort to understand the complex lives of migratory birds. This research provides data to help make more knowledgeable decisions both on a hemispheric and local scale. “Only by considering events throughout the entire annual cycle can well-informed decisions be made about how best to conserve and manage declining populations of migratory birds” (Rubenstein et al. 2002,1065).

A major obstacle to the conservation of Neotropical migrants arises from their very nature, they migrate across political boundaries. Even if we had all the answers to maintain these populations, the fact that they spend a portion of their lives in other countries makes conservation plans difficult to implement and enforce. Enormous amounts of time and money are spent to preserve breeding bird habitats, but without similar efforts in the wintering locations conservation efforts will not succeed. We in the U. S. have a vested interest in what happens on these wintering locations and the future health of our forest ecosystems depend on the preservation of lands thousands of miles away. In Dominica, the preservation of habitat for migrant birds also ensures that resident species, many of which are endemic to the island or region, are conserved for future generations. International collaboration is the key component to Neotropical migrant conservation, without which even our best conservation efforts will ultimately fail.

The dramatic decline of many of our Neotropical migratory birds has raised concern amongst scientists and bird watchers alike. Being an integral part of our ecosystem, these birds also bring great joy and pleasure to those who pursue them hoping for just a brief glimpse. We eagerly wait each spring the arrival of the birds from the south that fills our forests and fields with song. Their departure in the fall signals an end to the summer and an indication of the approaching winter. The loss of these birds would not only put our natural systems in peril but the world would be a much duller place to live.

Chapter 2

LITERATURE REVIEW

What is a Neotropical Migratory Bird?

Neotropical migratory birds breed in Canada and the U.S. in the summer and spend the winters in Mexico, Central America, South America and the Caribbean. More specifically, these birds occur in the Western Hemisphere, breed in the Nearctic (the area north of the Tropic of Cancer), and travel to the Neotropics (located south of the Tropic of Cancer) for the winter (Rappole 1995, DeGraff and Rappole 1995, and Faaborg 2002). The boundary between the Nearctic and the Neotropics is based on climate and vegetation and is not clearly defined. The Tropic of Cancer is used as the division of the Nearctic and the Neotropics for the purposes of determining the status of migrant birds. According to DeGraff and Rappole (1995, 9), “this border is reasonable biologically and provides a precise reference point when examining the breeding and wintering distributions of birds”. There are 361 species of Neotropical migrants, which include songbirds, shorebirds, raptors and waterfowl. Of these, songbirds (warblers, tanagers, vireos, orioles, sparrows) comprise the majority (DeGraff and Rappole 1995).

Migration

Neotropical migrants rely on multiple geographic locations (breeding, wintering, and stop-over) throughout their annual cycle. They require not only suitable habitat in which to spend the winter, but also appropriate stop over points along the way. As stated by DeGraff and Rappole (1995, 14), migration, though beneficial “may also expose migrants to a higher likelihood of extinction than resident species are exposed to, because of the multiplicity of environmental risks that migrants confront in an annual cycle.” Today, most threats to migrants are the result of human activities. Habitat destruction in all migratory areas is the major threat, but human population growth and pollution are also a concern (Rappole 1995 and Arendt 1992). Other perils faced during these yearly migrations include predation, finding sufficient food and the journey itself which can involve distances measured in thousands of miles and for many, nonstop flights across the Gulf of Mexico (Faaborg 2002). Many Neotropical migrants spend their lives in very specific regions in both their summer and winter homes. For example, populations of Black-throated Blue Warblers (Setophaga caerulescens) segregate themselves in their wintering grounds based on the geographic location where they breed [Fig. 1] (Rubenstein et al. 2002, Holmes 2007). Scientists are beginning to unravel the details of migratory connectivity using stable isotopes and genetic markers (Rubenstein et al. 2002, Kimura et al. 2002, Webster et al. 2002, Kelly et al. 2005, Boulet and Norris 2006). Should any one of these locations is degraded or destroyed; an entire population may be lost.

Despite these dangers migration has many benefits. By traveling northward in the spring these birds can take advantage of the abundant food supplies, namely insects, and numerous nesting sites that can be in short supply in the “crowded” tropics. The journey north also leads to decreases in the risk of density-dependent nest predation and parasitism which results in increased reproductive success (Alerstam and Hedenstrom 1998). According to Faaborg (2002), “A single tropical site may have more species breeding in it than have been recorded in whole states in the Temperate Zone”. The number of resident species increases the further you travel south, culminating with the incredible diversity of northern South America. Colombia, one of the most biologically diverse areas in the world, has nearly 1,700 species of birds (Faaborg 2002). More species means more competition and fewer resources. With this many species living in one place, it is no wonder that the majority of Neotropical migrants winter north of South America (Faaborg 2002).

When considering the entire life of an individual bird, the breeding and wintering grounds are equally important. It is also important to realize that we share these birds. The time spent here in the U.S. and Canada as ‘our’ birds is relatively brief compared to the time spent as ‘their’ birds on the wintering grounds. Many Neotropical migrant species spend up to ¾ of each

4 year on the wintering grounds (Arendt 1992). A complete understanding of these birds’ lives must go beyond the idea of a backyard bird and take on a global perspective. For these birds, ‘home’ is everywhere.

Evidence of Declines in Population

Many species of Neotropical migrants are experiencing long-term declines in their populations (Keller & Yahner 2006, Askins et al. 1990, Sauer & Droege 1992, Peterjohn et al 1995). Long-term studies such as the Breeding Bird Survey (BBS) in the U.S. and Canada have shown that declining trends are occurring at local and regional scales on the breeding grounds (Peterjohn et al. 1995, Sauer et al. 2008, see Sauer and Droege 1992). For example, Cerulean Warblers (Setophaga cerulea) are declining at a rate of 3% per year [Fig. 3] and Prairie Warblers (Setophaga discolor) at 1.5% per year [Fig. 4] across their breeding ranges (Sauer et al. 2008). Long-term research in New Hampshire at the Hubbard Brook Experimental Forest, a large unfragmented and relatively mature forest, has also demonstrated declines in Neotropical migrants [Fig. 2] (Holmes 2007).

Figure 2. “Thirty-seven-year trend in numbers of breeding birds occupying a 10-ha study area in northern hardwood forest at Hubbard Brook, New Hampshire, USA, 1969-2005. Numbers are totals for all species (males plus females) for permanent residents, short-distance migrants, long-distance (Neotropical) migrants and all species combined.” (From Holmes 2007, 3)

Figure 3. Cerulean Warbler (Setophaga cerulea), BBS Trend Map, 1966 – 2003 (From Sauer et al. 2008)

Figure 4. Prairie Warbler (Setophaga discolor) BBS Trend Map, 1966 – 2003 (From Sauer et al. 2008)

The reasons for these declines are not well understood, but researchers attribute them to two major causes: the loss and fragmentation of habitat on the breeding grounds (Latta and Baltz 1997, Faaborg 2002) and/or on the wintering grounds (Keller and Yahner 2006, Rappole and McDonald 1994). Habitat loss is a quantifiable loss of original habitat whereas fragmentation is the quantifiable loss plus a reduction in the habitat quality (Faaborg et al. 1995). Recently, some have suggested that a combination of habitat change on breeding and wintering grounds, along with habitat change on migratory stopover locations explains declines (Holmes 2007).

In fragmented habitats, size is also a measure of habitat quality. The concept of island biogeography (MacArthur and Wilson 1963) is used to explain some of the reasons behind decreased species richness in habitat fragments (Faaborg et al. 1995, Askins et al. 1990, Faaborg 2002, Laurance 2008). Many Neotropical migratory birds are habitat interior specialists and/or require a minimum habitat size. These species are “area sensitive” and tend to disappear from fragments that are many times larger than their territories (Faaborg et al. 1995). The surrounding habitat matrix is also important consideration. Patches of habitat surrounded by an early successional forest is likely to contain more species compared with the same habitat patch surrounded by intensive agriculture (Laurance 2008). Fragmented habitats are shown to negatively affect breeding birds due to decreased reproductive success and increased mortality resulting from higher rates of nest predation and parasitism and lower mate pairing success (Faaborg et al. 1995, Askins et al. 1990). Although the impacts of habitat loss and fragmentation on overwinter survival and success on the wintering grounds have been largely unexplored, there is some evidence that winter habitat quality can influence breeding success the following spring (Holmes 2007). A majority of the research on Neotropical migrants has focused on their breeding season ecology and/or the effects of forest fragmentation/habitat loss on these breeding populations (Faaborg et al 1995, Faaborg 2002, Donovan et al. 1995).

Aside from habitat loss and fragmentation, it is also uncertain whether migrant populations are most limited in their breeding or wintering grounds (Sherry and Holmes 1995, Sherry and Holmes 1996, Stillett and Holmes 2005, Holmes 2007, Sherry et al. 2005). Population limitations occur when factors such as food availability and the amount of suitable habitat constrain population numbers. For example, in North America the breeding areas cover a land area of about 16 million km2, but the major wintering areas cover only about 2.7 million km2 (Newton 2008). “Such a concentration of migrants is found nowhere else on Earth. […] Not only are the populations of many species highly compressed there, but more species are found together in the same area” (Newton 2008, 734). Consequently, the loss of one acre of habitat on the wintering grounds will have a greater impact than a similar loss on the breeding grounds (Faaborg 2002).

Research Needs

Overall, there is a tremendous shortage of information concerning Neotropical migrants on their wintering grounds and many ornithologists have expressed the need for much more research in this area, particularly in the Caribbean (Petit et al. 1995, Arendt et al. 1992, Sauer and Droege 1992). The Caribbean is of particular importance due to the extensive and rapid loss of habitat throughout much of the region. Only 11.3% of the Caribbean’s primary vegetation

7 remains (Myers et al. 2000). Furthermore, the continued destruction of habitat threatens not only migrant birds but also many endemic species found in one of the top ‘biodiversity hotspots’ on the planet (Myers et al. 2000). As a result of the loss of habitat, ornithologists have suggested that some species may be shifting their wintering ranges east and south from the more degraded islands in the west (Arendt et al. 1992). This possible change in the migratory routes comes mainly from anecdotal evidence suggesting that the extensive loss of habitat in places such as Cuba and Haiti will force the birds to move to more intact ecosystems in the eastern Caribbean. While Cuba does support the largest amount of forest in the Caribbean, the country is only about 20 % forested (FAO 2008). For perspective, compare to the seemingly forestless state of Ohio which boasts around 33% forest cover (ODNR). Deforestation in Cuba was the likely driver behind the extinction of Bachman’s Warbler (Vermivora bachmanii) (Newton 2008). Fortunately, Cuba, in addition to Puerto Rico, St. Vincent and the Grenadines has gained forest cover since 1990 (FAO 2008). Haiti, known for its severe environmental degradation, has only 3% of its total land covered in forest with continued losses (FAO 2008). Therefore, an understanding of the entire life cycle is essential, including the wintering grounds, if conservation efforts are to be successful.

Neotropical Migratory Birds Overwintering in the Caribbean

Avian research conducted in the Caribbean has focused overwhelmingly on the islands of the Greater Antilles (Cuba, Jamaica, Hispaniola, and Puerto Rico) and the Bahamas (Wunderle and Waide 1993, Wallace et al. 1996, Silwa and Sherry 1992, Faaborg and Arendt 1992, Confer and Holmes 1995) [Fig. 7]. Little information is available regarding the species composition, relative abundance and habitat occurrences of Neotropical migrants in the Lesser Antilles [Figures 7 & 8]. Much of the new information on migrants in the Lesser Antilles has been published as a result of recent bird banding efforts. Only four bird-banding stations have operated within the entire Lesser Antilles; they are stations in the British Virgin Islands, St. Martin, Barbados, and Guadeloupe (Brown and Collier 2004, McNair et al. 1999, Boal et al. 2006, Levesque 2008, pers. comm.). These banding stations are reporting species not previously thought to occur in the region or surprising numbers of individuals formerly considered rare. For example, the Yellow-billed Cuckoo (Coccyzus americanus) and the Northern Waterthrush (Parkesia noveboracensis) are both listed as accidentals for Dominica, yet the banding station in Guadeloupe, the island next door, reported 63 and 74 individuals respectively in 2007 (Levesque 2008, pers. comm.). Given the results from these banding efforts, it is likely that the same Neotropical migrant species occur on Dominica.

Collier and Brown (2004) banded on the island of St. Martin, approximately 200 miles NNW of Dominica, in a mangrove scrub forest and a secondary dry forest over January, February, and March of 2004. They captured 18 species of migrants and observed an additional four others. Of the 637 birds captured at their two sites within the secondary dry forest, they netted a total of 151 individuals from 17 species. Migrants accounted for nine of these species and 57 individuals - 31% of the birds captured. The mangrove scrub forest yielded 371 individuals from 17 species. Of these, migrants accounted for 7 species and only 10 individuals, about 3% of the total birds captured. Steadman et al. (2009) conducted point counts on St. John in the U.S. Virgin Islands during December 2005 and 2006. They recorded 17 species of

Neotropical migrants that accounted for 11.8% of total bird observations. Moist, mature forests yielded the most species and the most observations of Neotropical migrants. Because research on overwintering Neotropical migrants in the Lesser Antilles is limited, the adjacent Greater Antilles might reveal important clues to potential overwintering migrants. Wunderle and Waide (1993) surveyed 15 different habitat types on islands all across the Greater Antilles and the Bahamas. They found dry scrub and forest had the lowest migrant totals of all habitats sampled throughout the region. Mangroves were found to have the highest percentages of migrants. They also found that the American Redstart, Black-and-white Warbler and the Northern Waterthrush occurred most often in this habitat type. These findings are in line with other researchers in the Greater Antilles (Silwa and Sherry 1992, Wallace et al. 1996, Confer and Holmes 1995). Interestingly, Collier and Brown (2004) encountered more migrants in the secondary dry forest and Steadman et al. (2009) found more in moist mature forests, both contradicting Wunderle and Waide’s (1993) findings in the Greater Antilles and Bahamas. Looking at the variability between these three examples shows formulating overarching generalizations regarding overwintering Neotropical migrants would be irresponsible.

American Redstart (Setophaga ruticilla)

The American Redstart is a fairly common winter resident throughout much of the Caribbean. Its status in the Greater Antilles is well understood as it is one of the most studied species in the region (Brown and Collier 2004, Wallace et al. 1996, Wunderle and Waide 1993, Silwa and Sherry 1992). Little is known regarding the status of the American Redstart in the Lesser Antilles. The work of Brown and Collier (2004) on St. Martin is the most complete data set available. American Redstarts are medium-sized warblers with a distinctive plumage [Fig.5]. The plumage of the after-second Figure 5. American Redstart 3 after-second year male in year (ASY) male is black, orange, and white while the females Dominica. Photo by H. are gray, yellow, and white. The hatching year (HY) and second Roades. year (SY) males resemble females, although the second year males will often have a few black feathers and will be salmon colored instead of yellow. They breed across the eastern United States and Canada with a few localized populations in the northern western states and winter in Mexico, Central America, northern South American and the West Indies (Sherry and Holmes 1997, Dunn and Garrett 1997). As a habitat generalist during the non-breeding season, the American Redstart can be found in a variety of habitats across its wintering range. In the Caribbean, American Redstarts primarily occupy mangroves (Wunderle and Waide 1993). In addition to maintaining territories on their breeding grounds, American Redstarts will also establish and defend territories while on their wintering grounds (Holmes et al. 1989). The after-second year males are the most successful in acquiring a territory within a high quality habitat resulting in the young males and females being pushed into lower quality areas (Marra et al. 1993, Marra 2000). The females that

3 For age determination, all birds are given the birth date of January 1. For example, a bird that hatched in June 2009 is a hatch year (HY) bird until January 1st, 2010 when it becomes a second year (SY) bird and a second year (SY) bird becomes an after-second year bird (ASY).

9 were able to obtain a territory in the high quality habitat were larger and more aggressive than the females in the low quality habitats (Marra 2000). In addition to the age of the individual (HY/SY vs. ASY), the plumage brightness of the adult male American Redstart also plays a role in the ability to maintain a territory in a high quality habitat (Reudink et al. 2009). To determine optimal habitat for American Redstarts, Marra and Holberton (1998) measured the corticosterone levels of individuals wintering in scrub and mangrove habitats. Corticosterone is a hormone, secreted by the adrenal cortex, which increases in the body as it becomes more stressed. They found that birds wintering in the scrub had higher levels of corticosterone when compared to the birds wintering in mangroves, indicating that mangroves are of higher quality. This has further implications when considering the breeding success of these individuals the following spring. A bird wintering in a low quality habitat will most likely start their northward journey in less than optimal body condition (minimal fat reserves) making them more susceptible to adverse conditions (i.e. weather and loss of stop-over sites) they may encounter during migration and upon arriving at the breeding grounds are not in condition to commence nesting. By being habitat generalists, they may appear to be more resilient to habitat loss and degradation but this trait may also be a detriment to individuals and/or populations. Marra, Hobson, and Holmes (1998) found these same individuals acquired different isotopic signatures from the habitat in which they fed. Scrub habitats are dominated by C4 plants which results in the acquisition of high levels of 13C into the body, while mangrove habitats are 13 4 13 dominated by C3 plants which results in low C levels . Using C levels as the habitat type markers, they found that the American Redstarts arriving first on their breeding grounds in New Hampshire had low 13C levels compared to those that arrived later. American Redstarts are experiencing population increases in some regions while in others, the populations are decreasing. The driving factors behind these population changes are not well understood. Research is needed to determine the causes of these population changes and the connectivity between breeding and wintering locations (Sherry and Holmes 1997).

Northern Waterthrush (Parkesia noveboracensis)

The Northern Waterthrush is a locally common Neotropical migratory bird throughout the Caribbean. They are habitat specialists appearing to rely exclusively in mangrove habitats on the wintering grounds (Wunderle and Waide 1993, Wallace et al. 1996). Northern Waterthrushes are monomorphic (plumage characteristics same for both sexes) warblers that are brown backed with undersides that vary from whitish to yellowish in color and is streaked with brown. The supercilium is usually yellowish and tapers behind the eye [Fig.6]. They breed primarily in Canada and Alaska but can also be found in the north eastern states from Maine to New York and higher elevations in Pennsylvania and West Virginia. They also breed in the northern parts of Wisconsin and Michigan and portions of Montana, Idaho and Washington. Ohio has a very small portion of breeding birds in the extreme northeast. They

4 C3 plants (ex. wheat and soybeans) as a result of the Calvin cycle produce 3-phosphoglycerate as its first product. Hot, dry weather causes the stomata to close, effectively starving the plant of CO2, which limits the amount of food the plant can produce. C4 (ex. corn and sugarcane) plants fix carbon before the Calvin cycle, producing the 4-carbon containing oxaloacetate. This process allows the plant to use CO2 more efficiently in hot and dry environments and allows the plant to produce sufficient food even when the stomata are closed. 13C is a naturally occurring stable 13 isotope of carbon. C3 plants because of their method of carbon fixation have small amounts of C while C4 plants have high amounts of 13C (Campbell et al. 1999).

10 winter from Mexico to northern South America and the West Indies (Eaton 1995, Dunn and Garrett 1997). Throughout its breeding range, populations of the Northern Waterthrush appear stable. However, of concern are the mangrove habitats in the wintering range that are being lost at an increasing rate (Eaton 1995). According to Eaton (1995), “to assess needs and best approaches to conservation measures, more data are needed on the status, habits, and ecology of this species on its wintering grounds”. Considerably less data is available concerning the Northern Waterthrush within the Caribbean. In the Lesser Figure 6. Northern Antilles, Brown and Collier (2004) recorded Northern Waterthrush. Photo by H. Roades. Waterthrushes on St. Martin and Steadman et al. (2009) observed them on St. John. This may partly be due to the secretive nature of this species. They are drab, silent, and do not advertise themselves on their wintering grounds resulting in lower rates of detection. Because male and female Northern Waterthrushes have identical plumage, sex determination during the non-breeding season is not possible based on physical characteristics. But according to Reitsma, Hunt, Burson, and Steele (2002) the Northern Waterthrush, unlike the American Redstart, does not appear to segregate by sex on the wintering grounds.

Resident Species of Dominica

Like the migrants, research on resident species in the Lesser Antilles including Dominica is minimal. Only a few published research articles detail some of the birds found on Dominica. The most recent paper deals entirely with residents that were banded in 1978 in a fruit orchard at Bayac Estate (Prys-Jones 1982). As part of that study only 11 species were captured. James Bond (1928) described the status of birds on Dominica, St. Lucia, St. Vincent, and Barbados, focusing only on residents. Bond (1941) also described the nest and eggs many of the resident species of Dominica. Latta and Faaborg (2009, p. 292) demonstrate that research on the wintering grounds benefits both migrants and residents. They state that “[…] ecological research on wintering migrants often involves methodologies that provide information about the ecology and demography of little known tropical resident species, including new information on resident distributions, habitat requirements, community composition, and behavior.” By conducting research on the overwintering Neotropical migrants in the Lesser Antilles, we will learn more about the resident species that share part of their lives with the migrants.

New Ways to Study Migratory Birds

Emerging technologies have a very important role in helping to better understand bird migration in general and migratory connectivity, in particular. Migratory connectivity is, according to Boulet and Norris (2006, p.1), “the degree to which individuals or populations are geographically arranged among two or more periods of the annual cycle”. The use of stable isotopes is a very promising tool to geographically link the breeding and wintering locations of

11 individuals and populations of migrant birds (Hobson 2005, Hobson and Wassenaar 1997). Stable isotopes are biogeochemical markers that are used to “infer geographical origins” of animals (Rubenstein and Hobson 2004, 1). For migrant bird research the most common and useful stable isotope is deuterium (δD), an isotope of hydrogen. δD is naturally occurring in rainfall with levels decreasing with an increase in latitude (Rubenstein and Hobson 2004). As a result of rainfall the δD is integrated into the food web were it is then ingested and incorporated in the feathers of birds. The level of δD in the birds’ feathers allows estimates of the latitude where that feather was grown. Since birds only molt twice a year, once on the breeding grounds and once on the wintering grounds, the birds’ origins can be inferred (Hobson 2005). GIS is also being used in addition to the stable isotopes to further refine the links of migratory connectivity (Hobson et al. 2007). New advances in the size and weight of electronics have allowed geolocators to be used on migratory songbirds, birds that are too small for satellite tracking equipment. These geolocators detect the sunrise and sunset times which are used to determine locations. One recent study tracked Purple Martins (Progne subis) and Wood Thrushes (Hylocichla mustelina) throughout their fall migration, overwintering and spring migration. Data were collected on their migration routes, overwintering locations, stop-over locations, distance traveled, and migration phenology. Previously accepted estimates of migration rates appear to be very inaccurate with geolocators revealing Purple Martins completing a 7500 km journey in only 13 days, four of which were spent resting and feeding at stopover locations (Stutchbury et al. 2009).

Chapter 3

METHODS

Research Location

Dominica is located in the Lesser Antilles region of the Caribbean at 15° 30' N, 61° 25' W. It is situated to the south of Guadeloupe and north of Martinique. Dominica has a land area of 750.6 km² (Dominica 2001). The island has a rugged topography, due to its volcanic origins, with a maximum elevation of 1,447 m at Morne Diablatins. Dominica still retains many of its native ecosystems, including primary forest. The survival of which is owed to the fact that 70% of the country is considered “unsuitable for agriculture” (FAO 2008). The temperature averages 27ºC. Rainfall averages 445 cm per year, but averages 1016 cm annually in some locations (Dominica 2001).

Figure 7. The Caribbean with Dominica highlighted.

Figure 8. The Lesser Antilles. Puerto Rico is not part of the Lesser Antilles.

Research sites

Research was conducted at two locations during December 2008 and January 2009. Site one was located on the west-central side of Dominica near Roseau at Archbold Tropical Research and Education Center (ATREC) at Springfield Plantation [Fig. 9]. In this location, the dominant vegetation type is secondary rainforest (Dominica 2001). The second study site was located on the north-west section of the island near The Swamp at Cabrits National Park outside of Portsmouth [Fig. 9]. The dominant vegetation type found at this location was dry scrub forest and mangrove/swamp (Dominica 2001). These habitat types were selected based on previously published literature. Some of the highest numbers and diversity of species of Neotropical migrants within the Caribbean were found in similar forest types (Boal et al. 2006, Brown and Collier 2004, McNair et al. 1999, Wallace et al. 1996, Wunderle and Waide 1993). Secondary forest may or may not be preferred by overwintering migrants. Part of the reason behind the prevalence of migrants in secondary forest in other studies in the Caribbean is that most islands have no remaining primary forests (FAO 2008). This causes secondary forest to become very important habitat for over wintering migrants (Rappole 1995). Due to the extreme variability in vegetation types in this region, a secondary forest or a dry scrub forest can indicate a variety of different plant communities across the Caribbean and even within Dominica. This variability makes the selection of research locations with habitats similar to those in published literature difficult. Within the two research locations, the selection of the actual field sites used for mist-

14 netting was primarily the result of suggestions from in-country experts and accessibility of the site.

Figure 9. Location of the research sites within Dominica.

Cabrits National Park

Cabrits National Park is located in the northwest side of the island outside of Portsmouth [Figs. 9, 10 and 11]. The research site was located along a walking trail that bisected the Cabrits peninsula [Fig. 10]. The trail was approximately 645 meters long and 2 meters wide. The habitat varied greatly on either side of the trail, with the east supporting a swamp with mangroves while the west side of the trail was dominated by a dry-scrub forest [Fig. 12]. The differences in elevation was drastically different in each habitat type, with the swamp nearly at sea level while the dry-scrub side of the trail increased in elevation quickly and dramatically [Fig. 11]. The mist-nets were situated along an existing trail which eliminated the need to clear net lanes.

Figure 10. Cabrits National Park research site. The circle outlines the extent of The Swamp and the line illustrates the location of the trail used as a net lane.

Figure 12. Habitat types on each side of the research site at Cabrits National Park. On the left: dry- scrub forest. On the right: The Swamp with mangroves in the foreground. Photos by H. Roades.

Archbold Tropical Research and Education Center

Archbold Tropical Research and Education Center (ATREC) is located on the west side of Dominica near Canefield at approximately 457 meters in elevation [Fig. 13]. The area was dominated by mature secondary tropical rainforest. The mist-nets were located along an old estate road that climbed up the mountain side with an approximate change in elevation if 150 feet. [Fig. 14]. All banding operations were conducted from the Bee Cottage [Fig.13].

Figure 13. Location of research site at Archbold Tropical Research and Education Center (ATREC). The Bee Cottage was used as a banding station.

Research Location Banding Dates Number of Banding Days Cabrits National Park December 28, 2008 through 6 January 2, 2009 ATREC January 7 through January 9 15, 2009

Table 1. Banding dates and number of banding days by location.

Figure 14. Secondary rainforest along an old estate road used as a net lane at ATREC. Photo by H. Roades.

Mist-netting and Banding

Mist-netting and banding was conducted during December 2008 and January 2009. Each station consisted of seven to ten 12m x 2.6m, 36mm mesh, 4-tier nylon mist nets. At dawn nets were opened and operated for six hours each day depending on weather conditions (e.g. rain and/or high winds) (Bibby et al. 2000, Sutherland, Newton, and Green 2004). All birds captured were identified, aged and sexed (if possible) and wing chord, tarsal length, culmen length, tail length, fat scores and weight were recorded (Pyle 1997, Sibley 2000, Dunn and Garrett 1997, Raffaele et al. 2003, Sutherland, Newton, and Green 2004, and James et al. 2005). Hummingbirds were not banded due to the additional training, certification and special bands required. Neotropical migrants received a U.S. Geological Survey (USGS) aluminum leg band, while all resident species received non-USGS sequentially numbered bands. All birds captured were released alive.

Chapter 4

RESULTS

Mist-nets were operated for a total of 482 net hours at the two research locations (Ralph 1976). Even though the net hours were comparable for the two locations, 236 net hours at Cabrits and 246 net hours at ATREC, more nets were operated for longer hours over fewer days at Cabrits as opposed to fewer nets operated for less time over more days at ATREC. The mist-netting efforts resulted in a combined total of 203 individual birds from both locations, eight of which were recaptured on subsequent days for a total of 211 captures (Table 1). Recaptures were not included in the analysis. Of the 203 individuals captured, 159 were banded and 44 were released unbanded (Table 2). Birds were released unbanded when the proper size band was lacking, including the Broad-winged Hawk (Buteo platypterus) the Zenaida Dove (Zenaida aurita), and all hummingbirds. At ATREC, hummingbirds, particularly the Purple-throated Carib (Eulampis jugularis), accounted for 20 individuals captured. A total of 23 species were captured from both sites (Table 1). Neotropical migrants accounted for only two of the 23 species. Of the 23 species captured, 18 species were banded (Table 2). The five species that were not banded were the Lesser Antillean Hummingbird (Orthorhyncus cristatus), Purple-throated Carib (Eulampis jugularis), Green-throated Carib (Eulampis holosericeus), Zenaida Dove, and Broad-winged Hawk.

SPECIES CABRITS ATREC TOTAL American Redstart 3 0 3 Northern Waterthrush 3 0 3 Black-faced Grassquit 1 1 2 Plumbeous Warbler 2 12 14 “Golden” Yellow Warbler 4 0 4 Caribbean Elaenia 9 5 14 Bananaquit 5 34 39 Black-whiskered Vireo 3 0 3 Lesser Antillean Bullfinch 19 26 45 Lesser Antillean Saltator 8 0 8 Bare-eyed Robin 6 0 6 Scaly-breasted Thrasher 3 1 4 Common Ground Dove 2 0 2 Carib Grackle 1 0 1 House Wren 0 1 1 Lesser Antillean Flycatcher 0 6 6 Brown Trembler 0 3 3 Gray Kingbird 0 1 1 18 SPECIES 69 90 159

Table 2. Total birds banded by species and location.

SPECIES CABRITS ATREC TOTAL American Redstart 3 0 3 Northern Waterthrush 3 0 3 Black-faced Grassquit 1 1 2 Plumbeous Warbler 2 16 18 “Golden” Yellow Warbler 4 0 4 Caribbean Elaenia 9 5 14 Bananaquit 11 42 53 Black-whiskered Vireo 4 0 4 Lesser Antillean Bullfinch 19 31 50 Lesser Antillean Saltator 8 0 8 Bare-eyed Robin 6 0 6 Scaly-breasted Thrasher 3 1 4 Common Ground Dove 2 0 2 Carib Grackle 1 0 1 Antillean Crested Hummingbird 1 3 4 Zenaida Dove 1 0 1 Purple-throated Carib 0 18 18 Green-throated Carib 0 1 1 Broad-winged Hawk 0 1 1 House Wren 0 1 1 Lesser Antillean Flycatcher 0 6 6 Brown Trembler 0 3 3 Gray Kingbird 0 1 1 23 SPECIES 78 130 208

Table 3. Total birds captured by species and location.

Cabrits National Park

At this site a total of 236 net hours were recorded. A total of 69 individual birds were banded of the 78 individuals captured at this location between December 28, 2008 and January 2, 2009. Sixteen species were captured at this location, two of which were Neotropical migrants.

Migrants Captured at Cabrits

Two overwintering migrant species were captured, American Redstart (Setophaga ruticilla) and Northern Waterthrush (Seiurus noveboracensis), within the dry-scrub/mangrove swamp habitat. These two species contributed 3 individuals each for a total of 6 migrants [Table 3]. Migrants accounted for 7.7% of the total captures [Table 4] [Fig. 15]. One American Redstart was recaptured. Three other American Redstarts and one Black-and-white Warbler were observed at the site.

Number of Common Name Scientific Name Individuals 3 American Setophaga Redstart ruticilla 3 Northern Parkesia Waterthrush noveboracensis 6 TOTAL 2 TOTAL

Table 4. Neotropical migrant species and number of individuals captured at Cabrits National Park.

Residents Captured at Cabrits

Of the 16 species captured at Cabrits, fourteen were resident species (Table 5). Lesser Antillean Bullfinches (Loxigilla noctis) and Bananaquits (Coereba flaveola) accounted for the majority of the birds captured at 24% and 14% respectively (Fig. 15). Some species that were commonly encountered within these habitats such as the Yellow Warbler (Setophaga petechia), were only minimally represented in the capture data, with individuals representing only 5% of the total capture. Only three banded residents were recaptured.

Number of Individuals Common Name Scientific Name 1 Black-faced Grassquit Tiaris bicolor 2 Plumbeous Warbler Setophaga plumbea 4 “Golden” Yellow Warbler Setophaga petechia 9 Caribbean Elaenia Elaenia martinica 11 Bananaquit Coereba flaveola 4 Black-whiskered Vireo Vireo altiloquus 19 Lesser Antillean Bullfinch Loxigilla noctis 8 Lesser Antillean Saltator Saltator albicollis 6 Bare-eyed Robin Turdus nudigenis 3 Scaly-breasted Thrasher Allenia fusca 2 Common Ground Dove Columbina passerine 1 Carib Grackle Quiscalus lugubris 1 Antillean Crested Orthorhyncus cristatus Hummingbird 1 Zenaida Dove Zenaida aurita 72 TOTAL 14 TOTAL

Table 5. Resident species and number of individuals captured at Cabrits National Park.

Archbold Tropical Research and Education Center

In 246 net hours a total of 127 individual birds were captured, of which 90 were banded between January 7, 2009 and January 15, 2009. Only four individuals representing three species were recaptured. Fourteen species were captured at this location, none of which were Neotropical migrants.

Migrants Captured at ATREC

No migrants were captured or observed within the secondary rainforest habitat.

Residents Captured at ATREC

Fourteen resident species were captured within the secondary rainforest habitat located at the Archbold Tropical Research and Education Center (Table 6). Bananaquits and Lesser Antillean Bullfinches accounted for the majority of the birds caught representing 32% and 24% of the total captures respectively. The Purple-throated Carib (Eulampis jugularis), made-up 14% of the total individuals netted and represented the third most abundant species captured (Fig. 16). The hummingbirds were not banded so a portion of this could represent recaptured individuals, but considering the overall recapture rate it seems likely this accounted for only a small number of those captured.

Number of Individuals Common Name Scientific Name 16 Plumbeous Warbler Setophaga plumbea 1 Black-faced Grassquit Tiaris bicolor 5 Caribbean Elaenia Elaenia martinica 42 Bananaquit Coereba flaveola 1 House Wren Troglodytes aedon 6 Lesser Antillean Flycatcher Myiarchus oberi 31 Lesser Antillean Bullfinch Loxigilla noctis 3 Brown Trembler Cinclocerthia ruficauda 1 Gray Kingbird Tyrannus dominicensis 1 Scaly-breasted Thrasher Allenia fusca 18 Purple-throated Carib Eulampis jugularis 3 Antillean Crested Orthorhyncus cristatus Hummingbird 1 Broad-winged Hawk Buteo platypterus 1 Green-throated Carib Eulampis holosericeus 130 TOTAL 14 TOTAL

Table 6. Resident species and number of individuals captured at ATREC.

Neotropical migrant species were only detected at Cabrits National Park so comparisons between the two locations can only consist of presence verses absence.

The species tallies for Cabrits (16) and ATREC (14) were similar but composition varied. The majority of species were found at both locations, with only a few being unique to each location (Tables 7 & 8).

American Redstart Purple -throated Carib Northern Waterthrush Green-throated Carib Yellow Warbler Broad-winged Hawk Black-whiskered Vireo House Wren Lesser Antillean Saltator Lesser Antillean Flycatcher Bare-eyed Robin Common Ground Dove Brown Trembler Carib Grackle Gray Kingbird Zenaida Dove

Table 7. Species captured only at Table 8. Species captured only at Cabrits National Park. ATREC

SPECIES SCIENTIFIC NAME SPECIES CODE American Redstart Setophaga ruticilla AMRE Northern Waterthrush Parkesia noveboracensis NOWA Black-faced Grassquit Tiaris bicolor BFGR Plumbeous Warbler Setophaga plumbea PLWA* “Golden” Yellow Warbler Setophaga petechia YWAR Elaenia martinica CAEL Caribbean Elaenia Bananaquit Coereba flaveola BANA Black-whiskered Vireo Vireo altiloquus BWVI Lesser Antillean Bullfinch Loxigilla noctis LESB Lesser Antillean Saltator Saltator albicollis LAST* Bare-eyed Robin Turdus nudigenis BERO* Scaly-breasted Thrasher Allenia fusca SBTH* Common Ground Dove Columbina passerine CODO Carib Grackle Quiscalus lugubris CAGR* Brown Trembler Cinclocerthia ruficauda BRTR* Gray Kingbird Tyrannus dominicensis GRAK House Wren Troglodytes aedon HOWR Lesser Antillean Flycatcher Myiarchus oberi LESF Purple-throated Carib Eulampis jugularis PUTC*

Antillean Crested Hummingbird Orthorhyncus cristatus ANCH* Buteo platypterus BWHA Broad-winged Hawk Green-throated Carib Eulampis holosericeus GRTC* Zenaida Dove Zenaida aurita ZEND

Table 9. Species codes for birds captured. * Indicates species without Bird Banding Lab codes. Codes for these species were created.

ANCH ZEND BFGR 1% PLWA CAGR 1% 1% 3% 1% CODO SBTH 3% 4% NOWA LESB 4% 24% AMRE 4% YWAR 5% BWVI 5% BANA 14% BERO 8% LAST CAEL 10% 12%

Figure 15. Relative abundance for all species captured at Cabrits National Park. Neotropical migrants are in bold. See table 9 for species codes. HOWR SBTH GRTC BFGR GRAK BWHA 1% 1% 1% ANCH 1% 1% 1% 2% CAEL BRTR 4% 2% LESF 4% BANA 32%

PLWA 12%

PUTC 14% LESB 24%

Figure 16. Relative abundance for all species captured at ATREC. See table 9 for species codes.

Species Relative Abundance (%) Relative Abundance (%) Cabrits National Park ATREC AMRE 3.8 0 BFGR 1.3 0.8 PLWA 2.6 12.3 YWAR 5.1 0 NOWA 3.8 0 CAEL 11.5 3.8 BANA 14.1 32.3 HOWR 0 0.8 LESB 24.3 23.8 BWVI 5.1 0 LESF 0 4.6 BRTR 0 2.3 GRAK 0 0.8 LAST 10.3 0 BERO 7.7 0 SBTH 3.8 0.8 COGD 2.6 0 CAGR 1.3 0 ZEND 1.3 0 PUTC 0 13.8 GRTC 0 0.8 ANCH 1.3 2.3 BWHA 0 0.8

Table 10. Relative abundances in percent by species and location. See table 9 for species codes.

Chapter 5

DISCUSSION

Migrants in Dominica

Neotropical migrants were only detected at the Cabrits National Park location. Failure to detect them in the secondary rainforest of Archbold Tropical Research and Education Center (ATREC) was probably due to the difficulty in detecting individuals rather than their total absence. Long-term studies show that many species are not observed consistently but that does not mean that they are not present. Research in Puerto Rico has resulted in the capture of 20 species of Neotropical migrants, but some of these species have only been captured a few times in the 26 years of the study and only three species are captured every year (Faaborg 2002). An additional factor could account for the apparent lack of migrant species. Island biogeography – the smaller the island and the farther away from the mainland means less migrant species and/or that by increasing resident species there is a decrease in migrant species (Faaborg 2002). In Dominica, the capture of only two migrant species seemed insignificant but these two species accounted for about 8% of the total bird species sampled.

On St. Martin Collier and Brown (2004) captured ten Neotropical migrants of seven different species in the mangrove scrub habitat. These ten individuals accounted for only 2.7% of the total birds they captured compared to my results of 7.7%. Within the secondary dry forest they captured fifty-seven Neotropical migrants of nine different species. Collier and Brown (2004) banded over a longer time frame had more net hours (a total of 1958 net/hours), sampled a potentially richer site, and were closer in proximity to the Greater Antilles all of which could have influenced the increased migrant capture rate on St. Martin. It is most likely a combination of all of these factors. Unlike with their results, my secondary forest site, though a mesic forest, resulted in zero migrant captures.

Although I anticipated my findings to parallel the results of Collier and Brown (2004) due to the proximity of St. Martin to Dominica and the similar species compositions of the two locations my data fit most closely with that of Wunderle and Waide (1993). Their results mirrored my findings that the highest occurrence of migrants was in the mangrove habitat. The three species I encountered within the mangroves (American Redstart, Black-and-white Warbler, and Northern Waterthrush) were consistent with the species they found most often in that habitat. One confounding issue, however, is the dual nature of the habitat at Cabrits National Park. Because the research site was situated between two very different habitat types, mangrove/swamp and dry scrub forest, the assignment of preferred habitat for the three species captured can be difficult. Collier and Brown’s (2004) data also conflict with that of Wunderle and Waide (1993) in that the highest occurrences of migrants encountered was within the secondary dry forest and not the mangrove scrub forest. They also found 14 American Redstarts and 10 Black-and-white Warblers in the secondary dry forest compared to zero for both in the mangrove scrub forest. The habitat occurrences for the Northern Waterthrush were consistent in both studies as they are a habitat specialist restricted to mangroves on their wintering grounds. This leads me to question where the birds I captured were actually living; specifically, if the American Redstarts were originating in the mangrove/swamp habitat or in the dry scrub forest.

The conflicting nature of the available data highlights the need for further research efforts in the Caribbean and specifically the Lesser Antilles. Wunderle and Waide (1993) also found that habitat occurrences and rates of occurrence could vary between islands for the same species and different habitats yielded the most individuals depending on the island. These apparent differences could account for the discrepancies between Brown and Collier (2004), Wunderle and Waide (1993), and my own data. The majority of migrants could reside in an entirely different habitat especially since Dominica still retains some very rare primary forest. Due to Dominica’s relatively intact forests, the migrants that are overwintering there may be more evenly spread across the island. This could result in lower densities and hence lower detection rates. St. Martin is much smaller than Dominica and its habitats more degraded. This could cause the birds to maintain higher densities in much smaller habitat patches resulting in a higher detection rate. This could lead to the conclusion that St. Martin is an important overwintering location when it is really a habitat sink. The expansive nature of Dominica’s forests may harbor many Neotropical migrants that we failed to detect due to the limited nature of the research and access to appropriate locations. Even though the transect surveys were eliminated, it is worthy to note that three more (unbanded) American Redstarts (two female/SY males and one ASY male) were detected in addition to the three that were captured. A singe Black-and-white Warbler (Mniotilta varia) was also observed but not captured. According to Wunderle and Waide (1993), American Redstarts, Northern Waterthrushes, and Black-and-white Warblers occur on all islands in the Greater Antilles. Dr. Lennox Honychurch, the historian at Cabrits National Park, brought to my attention two bird bands that were recovered in May of 1993. The bands were USGS size 0 or 0A, which indicates the birds were Neotropical migrants and most likely a warbler species. Unfortunately, when the band numbers were reported to the bird banding lab the records for these bands were never submitted. This illustrates the importance of submitting banding data as a foreign band recovery is a very exciting and uncommon occurrence that would have provided valuable information regarding migrant birds in Dominica. These recoveries are what banding relies upon to generate an understanding of the lives of these migrant birds.

American Redstart American Redstarts segregate themselves by sex and age on the wintering grounds, potentially leading to a number of conservation issues (Holmes, Sherry, and Reitsma, 1998). If the high quality habitats, more frequently occupied by older males are protected, but the low quality habitats (more frequently occupied by females and young males) are degraded or developed, the future of this species could be at risk. Even the “low quality” habitats are very important to overwintering Redstarts and their loss could result in a population decline. The quality of a habitat that is occupied in the winter directly impacts on the quality of habitat that individual is able to obtain on their breeding grounds the following spring. Individuals overwintering in low quality habitats are more stressed which leads to a later arrival on the breeding grounds (Marra & Holberton 1998 and Marra et al. 1998). Arriving later results in increased competition for territories and nesting sites which lead to lower reproductive success for these individuals. Three American Redstarts were captured and three others sighted, all in the dry scrub/mangrove habitat. It is interesting to note that of the American Redstarts that were captured in Dominica, one was an after-second year male, one was a second year male and the

29 other was a second year female [Fig. 17]. Of the other three sighted birds two were either young males or females and one was an older male. This mix of age classes and sexes is interesting considering they are known to sexually segregate themselves on their wintering grounds, but the fact that the net lanes were situated between two habitat types of mangrove (high quality) and dry-scrub (low quality) may account for the distribution observed.

Figure 17. American Redstarts captured at Cabrits National Park. On left: SY female. Center: SY male. Right: ASY male.5 Photos by H. Roades.

Northern Waterthrush The only time Northern Waterthrushes were detected in Dominica was when they were captured in the mist-nets. The Waterthrushes were captured only in the dry scrub/mangrove habitat. They were completely silent as opposed to the relatively noisy American Redstarts. This silence most likely led to the Northern Waterthrush being underreported in my data. Because male and female Northern Waterthrushes have identical plumage, sex determination during the non-breeding season is not possible based on physical characteristics [Fig. 18]. But according to Reitsma and others (2002) the Northern Waterthrush does not segregate by sex on the wintering grounds. Because the Northern Waterthrush relies exclusively on mangrove habitats on its wintering grounds, habitat loss can make this species extremely vulnerable to population declines. Mangroves are already a limited habitat type found exclusively along coasts but developments (ex. beach side resorts) are often situated on this prime real estate.

Figure 18. Northern Waterthrushes captured at Cabrits National Park. Sexes unknown. Photos by H. Roades.

5 To eliminate confusion, all ages are given as they were on January 1. 30

Residents of Dominica

As a result of mist-netting efforts targeting Neotropical migrants, many resident species were also captured. Residents were banded utilizing the same protocol as migrants although non-USGS bands were used. While determining relative abundance of resident species was not the aim of this research it was necessary to establish resident species compositions in order to better understand the migrant species that contribute to the bird communities in Dominica. Lesser Antillean Bullfinches and Bananaquits were the most frequently encountered resident species captured at both research locations. Age and sex determination was difficult in a few of the resident species particularly Bananaquits, Lesser Antillean Saltator, and Plumbeous Warbler. The majority of the species found on Dominica had species accounts in the Identification Guide to North American Birds (Pyle 1997) which outlines the diagnostic characteristics for aging and sexing. However those species that do not occur in North America or are endemic to Dominica are not found in the guide and no guide exists outlining these criteria. Bananaquits proved to be especially difficult to age and sex due to the extreme variability seen within the individuals encountered. They exhibited a wide variety of color within the supercilium varying between white, yellow and white, or yellow by individual [Fig. 19]. The amount of grey feathers on the head varied by individual and did not appear to be tied to supercilium color. These color variations are not addressed in any of the field guides for Dominica or the West Indies. I suspect the individuals with a white supercilium are the after-second year individuals while those with yellow are younger, based on feather quality and feather characteristics such as wear, shape and coloration. Those with yellow supercilium tended to look “thread bare” sometimes with significant feather wear, growth bars on retrices, pointed primary coverts and minimal amounts of white on outer retrices. Secondly, the Bananaquits varied greatly in size. Those with a white supercilium were usually larger and were sometimes too large for the recommended band size. Prys-Jones (1982) found that adult birds were significantly larger than juvenile birds. The Plumbeous Warbler, an endemic to Dominica and Guadeloupe had distinctively yellow hued plumage in the young birds [Fig. 20]. This plumage coloration is not illustrated in any of the guides and caused a bit of confusion when they were initially captured. The documentation of these subtle plumage differences adds to the knowledge of the ageing and sexing for these species.

Figure 19. Bananaquits. Left: individual with white supercilium. Right: individual with yellow and white supercilium and grey on crown. Photos by H. Roades

Figure 20. Plumbeous Warblers. On left: adult. On right: juvenile. Photos by H. Roades

Research Limitations

Our field sites, thus net locations, were entirely dependent on access in a densely vegetated region. This resulted in the necessity to run nets in locations that were not necessarily the best locations for catching birds, possibly resulting in lower numbers of birds captured. Other locations such as the other side of the swamp and along the Indian River also support mangrove habitats that may harbor more individuals or other species of Neotropical migrants, but their lack of access is a major restriction to sampling these locations. Due to time constraints and lack of appropriate equipment, net-lanes could not be cut so existing openings and trails had to be utilized. Time was further constrained when all the research equipment failed to arrive for a full week resulting in a shorter banding period at the Cabrits National Park. Also, due to being restricted to areas accessible to the public the entire banding station, poles and all had to be dismantled every evening and reset every morning. The weight of birds captured after the first day were not recorded because the scale was stolen. At Cabrits rainfall was not a major issue although it resulted in a few late starts and early stops. Of greater concern, due to the close proximity to the ocean and the low vegetation on one side of the study site, were strong winds. Rain was an impediment at ATREC with heavy rains nearly every morning that resulted in a delay in setting up nets. In addition to the early morning rains, a heavy rain could occur at any time throughout the day. Fortunately, the nets were mostly protected under the tree canopy. Transect counts were discontinued due to constrains on time associated with running a banding station and our inability to visually detect nonvocalizing birds in the dense vegetation. Identification by song was not possible because most species do not sing during the non-breeding season and the unfamiliarity of the researcher with the vocalizations of the resident species. Due to the secretive nature of many Neotropical migrants on their wintering grounds, mist-netting provides a valuable tool to study birds that typically go unnoticed otherwise. Many of the overwintering Neotropical migrants are often overlooked because they are very small, have molted into their drab basic plumages, and do not sing. This secretive nature may account for the lack of basic information across much of their wintering range. It is notable that, mist- netting is biased due to the limited vertical reach of nets. Species that spend the majority of their time in the high tree canopy can potentially be missed. This may lead to reduced detection and inaccurate assessments of abundance or presumed absence. We found detecting Neotropical migrants in their wintering habitats is more difficult than during the breeding season.

Future Research

More habitat types and various locations within those habitat types need to be sampled to accurately establish migrant species compositions and abundances for Dominica. Future research should focus on the Indian River which has extensive mangrove habitat and the primary forests such as those found in Morne Diablotin and Morne Trois National Parks [see Fig. 21]. In the Caribbean, some of the highest abundances of overwintering Neotropical migrants are found within the mangrove forests (Arendt 1992, Silwa & Sherry 1992, Wunderle & Waide 1993). In addition, mangrove habitats are considered to be of high quality. The primary forests could potentially hold additional Neotropical migrants and because of the rarity of this habitat in the Caribbean, be an important migrant overwintering area. Because of the rugged nature and diverse topography of Dominica, small changes in elevation and orientation can have drastic consequences on the vegetation and bird assemblages found a given area. Many times these changes occur quite abruptly. This diversity creates difficulties with making generalizations across the island regarding the species composition, relative abundance, and habitat occurrence of Neotropical migrants found on Dominica and highlights the need for further research.

Conservation

The ultimate goal of much of the research on Neotropical migrants is to better understand the ecology of these birds in order to make better informed management decisions that will ensure their continued survival. This is especially critical considering that many migrant species are declining and we don’t really know why. Every little piece added to the puzzle allows the big picture to come into focus. Dealing with conservation issues, especially with migrant species, requires the best information available. When considering the importance of continuing research for conservation, Latta and Faaborg (2009, 289) put it best by saying, “some suggest that enough is known about wintering ecology to manage without further research; we suggest that such a thought is dangerous”. Faaborg and others (2010) suggest though not enough is known about the ecology of migrant birds, the research of the past 30 years has at least given us a starting point for conservation efforts. They also emphasize the importance of future research to address threats from human population growth, resource consumption, and global climate change. The status and conservation of Neotropical migrants in the Caribbean and throughout their wintering ranges in Mexico, Central America, and South America will also benefit from the development of MoSI (Monitoreo de Sobrevivencia Invernal), a program based on the breeding season MAPS (Monitoring Avian Productivity and Survivorship) protocol that tracks long-term population trends in overwintering species (DeSante et al. 2007). A beneficial next step would include implementing the MoSI program in Dominica. In addition to increasing the understanding of resident species as discussed by Latta and Faaborg (2009), research on overwintering migrants also increases capacity building, outreach and education, environmental organizations, management, and ecotourism within the host country (Latta and Faaborg 2009). Dominica is in the unique position that they already have the infrastructure and conservation programs in place. They currently have well maintained parks and extensive preserves aimed at protecting the two endemic parrot species and the natural ecosystems of the island [Fig. 21]. These parks and preserves in addition to maintaining resident species’ populations also fulfill the needs for many migrant species. Migrant species can be

33 protected without extensive changes or additions to current conservation initiatives within Dominica. Based on my results, the area with the highest conservation priority in regard to Neotropical migrants is The Swamp at Cabrits National Park. The mangrove community is an important habitat for migrant and resident birds based on my research and the research of others in the Caribbean. The mangrove community is relatively limited within Dominica with only a few other stands in the Portsmouth area. The limited nature of this habitat is further compounded by the proposed development of the shoreline at The Swamp to make way for a marina. The development will undoubtedly impact The Swamp which is only feet away from the proposed marina site. Part of this research highlights just how important The Swamp is for migrants and residents. Optimistically, this will open the door to future cooperation in Neotropical migrant conservation.

Figure 21. Protected lands within Dominica (from Dominica 2000).

Conclusions

My research established the species composition, relative abundance, and habitat occurrence of Neotropical Migratory birds overwintering in two habitat types in Dominica. More specifically I found:

1. Three species of Neotropical migrants: American Redstart, Northern Waterthrush, and Black-and-white Warbler. 2. American Redstarts and Northern Waterthrushes each accounted for 4% of the total birds captured. The Black-and-white Warbler was not captured so it cannot be accounted for in the relative abundance. 3. All Neotropical migrants detected occurred in the dry scrub/mangrove habitat at Cabrits National Park.

The data I collected are preliminary in nature and serves as a base-line for future research. Considering that to accurately establish species compositions and abundances for a single site, multiple seasons of data are required (Latta and Faaborg 2009). Increased research throughout the Caribbean and especially the Lesser Antilles is integral to ensure that the proper conservation strategies are enacted. Within the Lesser Antilles, Dominica holds the unique position of sustaining a rich habitat for Neotropical migrants, but lacks research on the Neotropical migrants occurring there. My research establishes that Neotropical migratory birds do overwinter on Dominica and leads to additional questions concerning migrants on Dominica such as:

1. Do any other habitat types, such as primary forest, contain Neotropical migrants? 2. How many species of migrants pass through Dominica during migration? 3. Do species and individuals consistently overwinter on Dominica every year? 4. What impact does elevation have on the species composition and abundance of migrants? 5. How do the migrants overwintering in Dominica compare to those overwintering on other islands in the Lesser Antilles, such as Guadeloupe and Martinique?

Unfortunately, due to the lack of relevant data and the geographical and biological variability between islands, broad generalizations cannot be made for Dominica, the Lesser Antilles, or the Caribbean. We are warned about making generalizations when John Faaborg (2002) says, “can we make any generalizations about ‘the winter ecology’ of Neotropical migrants? Not if we want to make any sense. There is too much we do not understand about what is going on with these species during the majority of their annual cycle.” Considering this I can say that, based on the work of others in the Caribbean and specifically Brown and Collier (2004) in St. Martin, there are likely many more migrant species overwintering on Dominica and further research will reveal them.

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