Conservation of migratory birds necessitates protecting suitable stopover habitat along migratory routes as well as destination habitats, especially near large geographic barriers such as the Gulf of Mexico. The Florida Keys (Keys) are an important stopover and breeding destination for migratory landbirds. We documented 47 migratory and 21 resident landbird species via point counts during March–May 2004 and 2005. As a group, species richness, species diversity, and the effective number of species of migratory landbirds, including several species of conservation concern, was significantly and positively associated with percent cover of tropical hardwood hammock, a threatened upland forest type. The collective resident landbird community in the Keys was negatively associated with native hammock cover, although species diversity of the resident community was positively associated with the proximity of native hammock and several resident species, including species of conservation concern, were commonly or predominantly associated with native hammock. Consequently, conservation of native hammock habitat in the Keys is an important conservation priority for migratory birds and several resident species of conservation concern.
The loss and fragmentation of native plant communities used as breeding and wintering grounds is recognized as a serious threat to the conservation of migratory birds [
The Florida Keys (Keys) are a chain of low-lying islands that extend from the southeastern tip of Florida and arc in a southwesterly direction to the Dry Tortugas [
Tropical hardwood hammocks (hammocks) are closed canopy forests characterized by a diverse suite of evergreen and semideciduous woody species primarily of West Indian origin, many or most of which are producers of mast [
Although hammocks are believed to provide important habitat for migratory and resident birds [
The Keys archipelago (Figure
Florida Keys archipelago and study area located off the southern tip of Florida, USA.
Hammocks in the Keys support high plant diversity and are dominated by evergreen and semi-deciduous woody species, most of which produce mast and are of West Indian origin [
We conducted morning bird surveys between sunrise and 180 minutes after sunrise as 20 m fixed-radius point counts with 5-min survey intervals [
Point count locations were identified by creating a Geographical Information Systems (ESRI GIS Software ArcMap 9.0) database of all protected hammocks and residential areas [
We established 86 point count locations, 27 (31%) of which were in native hammocks and 59 (69%) of which were in residential areas with varying amounts of native hammock, canopy with open understory, and other cover types. We quantified 4 site variables and 2 landscape variables at each point count location (Table
Description and quantification (mean and standard deviation, median and range) of site and landscape variables at protected and residential sites where bird surveys were conducted (20-m fixed radius point counts) in the Florida Keys during March–May 2004 and 2005.
Variable | Description | Protected sites | Unprotected sites | ||||||
Mean | SD | Median | Range | Mean | SD | Median | Range | ||
PCT_HAM | Site variable: percent cover of native hammock canopy with intact understory | 96 | 8 | 100 | 65–100 | 18 | 30 | 0 | 0–100 |
PCT_CAN | Site variable: percent cover of native hammock tree canopy cover with cleared understory | <1 | 1 | 0 | 0–6 | 18 | 16 | 15 | 0–65 |
PCT_LAWN | Site variable: percent cover of residential lawn (turfgrass, ornamental plantings, pavement, and structures) | 1 | 2 | 0 | 0–10 | 10 | 11 | 6 | 0–35 |
PCT_OTHER | Site variable: percent cover of nonhammock vegetation (e.g., marsh, mangroves, pinelands) | <1 | 2 | 0 | 0–8 | 1 | 5 | 0 | 0–27 |
D2HAM | Landscape variable: distance (m) to closest hammock (if survey site was located within a hammock, D2HAM = 0) | 0 | 0 | 0 | 0 | 59 | 83 | 26 | 0–417 |
SIZEHAM | Landscape variable: size (ha) of closest hammock (if survey site was within a hammock, the size of that hammock was recorded) | 29 | 30 | 13 | 1–70 | 7 | 19 | <1 | <1–87 |
We surveyed birds at each point count location 5 times for each field season with the exception of 1 protected hammock where 2 locations were surveyed 4 times during 2004 because permission to access the hammock was delayed. The northern- and southern-most point count locations were separated by approximately 97 km, so we randomly ordered groups of point count locations and alternated the direction in which bird surveys were conducted. We conducted point counts at approximately 16 locations per morning.
During surveys, we recorded all birds detected by call, song, or sight within the 20-m point count radius (excluding flyovers) and identified each to species. For each species detected we recorded presence (frequency) and abundance (Table
Migratory (MS) and year-round resident (YR) species recorded during point counts in the Florida Keys during March–May 2004 and 2005 in residential and conservation areas with varying levels of intact native hammock forest cover. Species are listed from most frequently to least frequently observed during point counts. Total observations are reported for each species as frequency (number of point counts in which species was recorded) and abundance (total number of birds recorded). Percent frequency and percent abundance are provided in parentheses and reflect the relative frequency and abundance of each species within its migratory classification. Detection rates (frequency and abundance) are provided for each species for point count sites categorized by the amount of native hammock cover present: <10% (42 sites,
Species, migratory classification, and life-history notes | Total observations | Detection rate (frequency) | Detection rate (abundance) | |||||
by % hammock cover | by % hammock cover | |||||||
Frequency (%) | Abundance (%) | <10% | 15–52% | 65–100% | <10% | 15–52% | 65–100% | |
Migratory Species (MS) ( | ||||||||
PalmWarblera | 157 (20) | 468 (29) | 0.186 | 0.182 | 0.179 | 0.624 | 0.453 | 0.481 |
Gray Catbirda | 149 (19) | 251 (16) | 0.171 | 0.153 | 0.190 | 0.312 | 0.277 | 0.272 |
Black-whiskered Vireocde | 51 (7) | 63 (4) | 0.019 | 0.065 | 0.119 | 0.019 | 0.106 | 0.138 |
American Redstarta | 48 (6) | 107 (7) | 0.043 | 0.065 | 0.071 | 0.098 | 0.118 | 0.172 |
Gray Kingbirdc | 45 (6) | 87 (5) | 0.079 | 0.047 | 0.015 | 0.162 | 0.077 | 0.022 |
Black-and-white Warblera | 44 (6) | 97 (6) | 0.019 | 0.047 | 0.105 | 0.038 | 0.124 | 0.224 |
Red-eyed Vireob | 38 (5) | 48 (3) | 0.012 | 0.018 | 0.112 | 0.014 | 0.018 | 0.146 |
White-crowned Pigeoncde | 30 (4) | 53 (3) | 0.026 | 0.041 | 0.045 | 0.045 | 0.065 | 0.086 |
Ovenbirda | 28 (4) | 31 (2) | 0.002 | 0.047 | 0.071 | 0.002 | 0.059 | 0.075 |
Blue-gray Gnatcatchera | 26 (3) | 41 (3) | 0.014 | 0.018 | 0.063 | 0.026 | 0.029 | 0.093 |
Blackpoll Warblerb | 20 (3) | 41 (3) | 0.026 | 0.018 | 0.022 | 0.055 | 0.059 | 0.030 |
Common Yellowthroata | 15 (2) | 31 (2) | 0.007 | 0.047 | 0.015 | 0.014 | 0.106 | 0.026 |
Eastern Kingbird | 14 (2) | 17 (1) | 0.029 | 0.006 | 0.004 | 0.033 | 0.006 | 0.008 |
Black-throated Blue Warblera | 11 (1) | 16 (1) | 0.010 | 0.012 | 0.019 | 0.014 | 0.018 | 0.026 |
Cape May Warblera | 11 (1) | 27 (2) | 0.010 | 0.012 | 0.019 | 0.017 | 0.012 | 0.067 |
Indigo Buntinga | 11 (1) | 33 (2) | 0.019 | 0.018 | 0.000 | 0.057 | 0.053 | 0.000 |
Worm-eating Warblerb | 9 (1) | 10 (1) | 0.002 | 0.000 | 0.030 | 0.002 | 0.000 | 0.034 |
Magnolia Warblerb | 8 (1) | 31 (2) | 0.007 | 0.024 | 0.004 | 0.012 | 0.124 | 0.019 |
Blackburnian Warblerb | 6 (1) | 15 (1) | 0.005 | 0.018 | 0.004 | 0.019 | 0.035 | 0.004 |
Brown-headed Cowbirdad | 6 (1) | 9 (1) | 0.014 | 0.000 | 0.000 | 0.021 | 0.000 | 0.000 |
Yellow-throated Warblera | 6 (1) | 9 (1) | 0.005 | 0.012 | 0.008 | 0.010 | 0.012 | 0.011 |
Painted Buntingae | 3 (<1) | 4 (<1) | 0.005 | 0.000 | 0.004 | 0.007 | 0.000 | 0.004 |
Wood Thrushb | 3 (<1) | 5 (<1) | 0.002 | 0.000 | 0.008 | 0.005 | 0.000 | 0.011 |
Yellow-billed Cuckooacd | 3 (<1) | 4 (<1) | 0.000 | 0.000 | 0.011 | 0.000 | 0.000 | 0.015 |
Yellow-rumped Warblera | 3 (<1) | 3 (<1) | 0.002 | 0.000 | 0.008 | 0.002 | 0.000 | 0.008 |
Yellow-throated Vireoab | 5 (1) | 6 (<1) | 0.007 | 0.000 | 0.008 | 0.010 | 0.000 | 0.008 |
American Kestrela | 2 (<1) | 2 (<1) | 0.002 | 0.006 | 0.000 | 0.002 | 0.006 | 0.000 |
Eastern Phoebea | 2 (<1) | 3 (<1) | 0.002 | 0.000 | 0.004 | 0.002 | 0.000 | 0.008 |
Hooded Warblerb | 4 (1) | 6 (<1) | 0.002 | 0.000 | 0.011 | 0.002 | 0.000 | 0.019 |
Merlina | 2 (<1) | 2 (<1) | 0.005 | 0.000 | 0.000 | 0.005 | 0.000 | 0.000 |
Nashville Warbler | 2 (<1) | 4 (<1) | 0.002 | 0.000 | 0.004 | 0.007 | 0.000 | 0.004 |
Pine Warblera | 2 (<1) | 2 (<1) | 0.002 | 0.000 | 0.004 | 0.002 | 0.000 | 0.004 |
Prothonotary Warbler | 2 (<1) | 2 (<1) | 0.002 | 0.000 | 0.004 | 0.002 | 0.000 | 0.004 |
Ruby-throated Hummingbirda | 2 (<1) | 4 (<1) | 0.005 | 0.000 | 0.000 | 0.010 | 0.000 | 0.000 |
Scarlet Tanagerb | 2 (<1) | 5 (<1) | 0.000 | 0.006 | 0.004 | 0.000 | 0.012 | 0.011 |
Summer Tanagerb | 2 (<1) | 4 (<1) | 0.000 | 0.006 | 0.004 | 0.000 | 0.018 | 0.004 |
Swainson's Warbler | 2 (<1) | 2 (<1) | 0.000 | 0.000 | 0.008 | 0.000 | 0.000 | 0.008 |
Blue Grosbeakb | 1 (<1) | 2 (<1) | 0.002 | 0.000 | 0.000 | 0.005 | 0.000 | 0.000 |
Cedar Waxwinga | 1 (<1) | 45 (3) | 0.002 | 0.000 | 0.000 | 0.107 | 0.000 | 0.000 |
Common Nighthawkc | 1 (<1) | 1 (<1) | 0.000 | 0.000 | 0.004 | 0.000 | 0.000 | 0.004 |
Northern Parulaa | 1 (<1) | 4 (<1) | 0.000 | 0.006 | 0.000 | 0.000 | 0.024 | 0.000 |
Northern Rough-winged Swallowa | 1 (<1) | 1 (<1) | 0.000 | 0.000 | 0.004 | 0.000 | 0.000 | 0.004 |
Rose-breasted Grosbeakb | 1 (<1) | 1 (<1) | 0.002 | 0.000 | 0.000 | 0.002 | 0.000 | 0.000 |
Ruby-crowned Kingletb | 1 (<1) | 1 (<1) | 0.000 | 0.000 | 0.004 | 0.000 | 0.000 | 0.004 |
Tree Swallowa | 1 (<1) | 1 (<1) | 0.000 | 0.006 | 0.000 | 0.000 | 0.006 | 0.000 |
Yellow-bellied Sapsuckera | 1 (<1) | 1 (<1) | 0.000 | 0.000 | 0.004 | 0.000 | 0.000 | 0.004 |
Yellow-breasted Chatb | 1 (<1) | 1 (<1) | 0.000 | 0.000 | 0.004 | 0.000 | 0.000 | 0.004 |
Migratory totals (Freq., Abun.) and mean detection rates | 784 (100) | 1601 (100) | 0.016 | 0.019 | 0.026 | 0.038 | 0.039 | 0.044 |
Resident Species (YR) | ||||||||
Northern Cardinal | 473 (20) | 962 (21) | 0.457 | 0.635 | 0.646 | 0.902 | 1.341 | 1.325 |
Eurasian Collared Dovef | 455 (19) | 1097 (24) | 0.757 | 0.618 | 0.119 | 2.000 | 1.229 | 0.179 |
Red-bellied Woodpecker | 381 (16) | 533 (11) | 0.574 | 0.477 | 0.220 | 0.857 | 0.629 | 0.246 |
Blue Jay | 177 (7) | 310 (7) | 0.298 | 0.229 | 0.049 | 0.514 | 0.400 | 0.097 |
Common Grackle | 159 (7) | 461 (10) | 0.245 | 0.212 | 0.075 | 0.738 | 0.729 | 0.101 |
Northern Mockingbird | 134 (6) | 195 (4) | 0.257 | 0.129 | 0.015 | 0.381 | 0.182 | 0.015 |
Mourning Doveg | 131 (5) | 185 (4) | 0.217 | 0.159 | 0.049 | 0.321 | 0.212 | 0.052 |
Great Crested Flycatcherg | 103 (4) | 133 (3) | 0.164 | 0.100 | 0.063 | 0.221 | 0.129 | 0.067 |
Red-winged Blackbirdg | 101 (4) | 206 (4) | 0.157 | 0.082 | 0.078 | 0.383 | 0.135 | 0.082 |
White-eyed Vireog | 88 (4) | 143 (3) | 0.005 | 0.077 | 0.272 | 0.005 | 0.129 | 0.444 |
European Starlingf | 86 (4) | 250 (5) | 0.188 | 0.035 | 0.004 | 0.533 | 0.135 | 0.011 |
Prairie Warblereg | 42 (2) | 66 (1) | 0.026 | 0.024 | 0.101 | 0.038 | 0.059 | 0.149 |
Red-shouldered Hawkg | 33 (1) | 38 (1) | 0.033 | 0.053 | 0.037 | 0.041 | 0.059 | 0.041 |
Common Ground-doveeg | 13 (1) | 16 (<1) | 0.014 | 0.018 | 0.015 | 0.019 | 0.018 | 0.019 |
Northern Flickerg | 12 (1) | 15 (<1) | 0.010 | 0.024 | 0.015 | 0.014 | 0.024 | 0.019 |
Mangrove Cuckooeh | 11 (1) | 13 (<1) | 0.000 | 0.000 | 0.041 | 0.000 | 0.000 | 0.049 |
White-winged Dovefg | 9 (<1) | 14 (<1) | 0.017 | 0.012 | 0.000 | 0.026 | 0.018 | 0.000 |
Carolina Wren | 4 (<1) | 6 (<1) | 0.000 | 0.000 | 0.015 | 0.000 | 0.000 | 0.022 |
Monk Parakeetf | 4 (<1) | 14 (<1) | 0.002 | 0.018 | 0.000 | 0.002 | 0.077 | 0.000 |
Great Horned Owl | 1 (<1) | 1 (<1) | 0.000 | 0.000 | 0.004 | 0.000 | 0.000 | 0.004 |
Yellow Warblere | 1 (<1) | 1 (<1) | 0.000 | 0.006 | 0.000 | 0.000 | 0.006 | 0.000 |
Resident totals (Freq., Abun.) and mean detection rates | 2418 (100) | 4659 (100) | 0.163 | 0.139 | 0.087 | 0.333 | 0.262 | 0.139 |
aNeotropical migrant that includes individuals that winter and stopover in the Florida Keys.
bNeotropical migrant that uses the Florida Keys exclusively or primarily as stopover habitat.
cNeotropical migrant that includes individuals that use the Florida Keys primarily as a breeding destination.
dResident population may be established in Florida Keys, but majority of individuals thought to be migratory.
eBird of Conservation Concern [
fNonnative species.
gYear-round resident population exists in Florida Keys, but migratory individuals also travel to Keys as a winter destination.
hHistorically considered migratory with Florida Keys a breeding destination, but evidence for migration is weak, winter sightings have been documented, and resident population suspected.
Each species recorded was classified as either a year-round resident (YR) or as a migratory species (MS), which included migratory species that use the Keys as wintering habitat, as a breeding destination, or as stopover habitat during migration (Table
At each point count location we calculated 3 community measures separately for MS and YR, total species richness, species diversity, and the effective number of species. Species richness was calculated as the total number of species observed at each location. We used the Shannon-Wiener index (Shannon entropy) as an index of species diversity because it is sensitive to changes in the abundance of rare species in a community [
We developed separate heterogeneous slopes models to evaluate the influence of independent landscape and site variables (Table
In exploratory analyses we found that MS and YR had different error term variances in each case, so we also allowed for unequal variances in the two groups. Further, because the same measures were conducted for MS and YR at all sites, a random block effect for site was included in the model. Interaction terms were used to test whether the slopes of the relationships between each community measure (e.g., species richness) and the independent variables were the same for MS and YR. When the slopes for a particular independent variable are not statistically different this implies that the relationship between the community measure and the independent variable was not statistically different between MS and YR. The subsequent step removed the interaction term and tested whether the slope between diversity and the explanatory variable is nonzero. If there was not a statistically significant relationship, that variable was removed from the model in a stepwise elimination procedure. The final model contained only those explanatory variables found to be statistically significant and also generated the smallest Akaike information criterion (AIC) value of the models tested. Statistical analyses were conducted using the GLIMMIX Procedure in SAS Version 9.2 (Copyright 2008, SAS Institute, Inc.).
During March–May 2004 and 2005, we conducted 858 point counts at 86 locations and recorded 78 species of birds that numbered 6400 individuals (Table
The response to site and landscape variables (Table
Heterogeneous slopes model results used to evaluate the influence of site and landscape variables on species richness, species diversity (using Shannon-Wiener index values), and the effective number of species (converted from Shannon-Wiener Index values; [
Species richness final model solutions (AIC = 795.57)
Effect | Group ID | Estimate | Std. error | DF | Pr > | |
---|---|---|---|---|---|---|
Group | MS | 5.04 | 0.36 | 162 | 14.14 | <0.01 |
YR | 9.63 | 0.24 | 162 | 39.47 | <0.01 | |
SIZEHAM | MS & YR | −0.02 | 0.07 | 162 | −2.35 | 0.02 |
PCT_HAM*group | MS | 0.03 | 0.01 | 162 | 3.99 | <0.01 |
YR | −0.03 | 0.01 | 162 | −6.23 | <0.01 |
Species diversity final model solutions (AIC = 203.52)
Effect | Group ID | Estimate | Std. error | DF | Pr > | |
---|---|---|---|---|---|---|
Group | MS | 1.28 | 0.12 | 162 | 10.79 | <0.01 |
YR | 2.02 | 0.08 | 162 | 26.69 | <0.01 | |
D2HAM | MS & YR | <−0.01 | <0.01 | 162 | −2.10 | 0.04 |
SIZEHAM | MS & YR | <−0.01 | <0.01 | 162 | −2.14 | 0.04 |
PCT_CAN*group | MS | <0.01 | <0.01 | 162 | 0.79 | 0.43 |
YR | −0.01 | <0.01 | 162 | −3.35 | <0.01 | |
PCT_HAM*group | MS | <0.01 | <0.01 | 162 | 2.84 | 0.01 |
YR | −0.01 | <0.01 | 162 | −7.95 | <0.01 | |
CT_OTHERHAB*group | MS | −0.03 | 0.01 | 162 | −2.47 | 0.02 |
YR | 0.01 | 0.01 | 162 | 1.58 | 0.12 |
Effective number of species final model solutions (AIC = 678.45)
Effect | Group ID | Estimate | Std. error | DF | Pr > | |
---|---|---|---|---|---|---|
Group | MS | 4.06 | 0.49 | 162 | 8.27 | <0.01 |
YR | 7.25 | 0.35 | 162 | 20.89 | <0.01 | |
D2HAM | MS & YR | <−0.01 | <0.01 | 162 | −2.24 | 0.03 |
SIZEHAM | MS & YR | −0.01 | <0.01 | 162 | −2.19 | 0.03 |
PCT_CAN*group | MS | 0.01 | 0.02 | 162 | 0.65 | 0.51 |
YR | −0.04 | 0.01 | 162 | −3.89 | <0.01 | |
PCT_HAM*group | MS | 0.02 | 0.01 | 162 | 2.63 | 0.01 |
YR | −0.04 | <0.01 | 162 | −7.97 | <0.01 | |
PCT_OTHERHAB*group | MS | −0.06 | 0.05 | 162 | −1.30 | 0.20 |
YR | 0.08 | 0.03 | 162 | 2.50 | 0.01 |
SIZEHAM was consistently associated with decreased species richness, diversity, and the effective number of species for both MS and YR (Table
Species diversity and the effective number of species, but not species richness, also decreased for both MS and YR as the distance from the nearest native hammock (D2HAM) increased (Table
Percent canopy cover with cleared understory (PCT_CAN) did not significantly influence any community measure for MS or species richness for YR, but was negatively associated with species diversity and effective number of species for YR (Table
We documented 8 species (4 MS, 4 YR) listed by the US Fish and Wildlife Service [
Mean frequency (presence) detection rates at point count sites categorized by percent hammock cover for migratory and resident species designated as species of conservation concern by the U.S. Fish and Wildlife Service [
Migratory birds (MS) recorded in the Keys during the spring migration and breeding period were the more species-rich group recorded, with greater than twice as many species as YR. However, in terms of abundance, the number of individuals of YR was nearly 3 times greater than MS. As collective groups, MS and YR species demonstrated different habitat requirements as measured by their response to site and landscape variables. These results illustrate the value of differentiating between migratory and resident species and quantifying community measures such as species richness and diversity measures when evaluating the importance of habitat variables as stopover or destination habitat for migratory birds.
The most important finding was the consistent and opposite response of MS and YR, as collective groups of species, to percent cover of native hammock forest with intact understory. Percent cover of native hammock (PCT_HAM) was a significant positive influence on species richness, species diversity, and effective number of species of MS. These results suggest that the majority of migratory species recorded in the Keys were dependent upon or preferred this native forest community. This does not mean, however, that all MS rely on native hammock cover. For example, some species such as the Palm Warbler (
Percent canopy cover with cleared understory (PCT_CAN), a site variable associated with residential areas, did not significantly influence species richness, species diversity, or the effective number of species of MS. These results indicate that the availability of tree canopy cover in residential areas cannot provide an adequate substitute for native hammock communities for many MS. However, the absence of a negative influence also suggests tree canopy cover is likely important for many migratory species. A notable example includes the White-crowned Pigeon, which was more often recorded in areas with greater hammock cover but was also observed feeding in the canopy of trees in residential areas with little or no native hammock understory (Figure
The negative relationship between species diversity and the effective number of species of MS and the percent cover of other habitats (PCT_OTHERHAB), such as mangroves, pine, and wetlands needs to be placed in context and should not be interpreted to suggest that these other habitats were unimportant to MS. The objective of this study was to evaluate the role of native hammock cover and residential areas with varying amounts of hammock and tree canopy cover. These other habitat types, while present at many point count sites, averaged
The negative influence of the two landscape variables on species richness and diversity measures for MS includes interpretation that is also somewhat speculative. The findings that species diversity and the effective number of species of MS decreased as the distance to the nearest hammock (D2HAM) increased seem straightforward and suggest that MS were attracted to hammocks and numbers of MS were greater in surrounding areas near hammocks. This interpretation is consistent with the influence of site variables, that is, that MS were positively associated with hammock cover. However, the negative relationship between the size of the nearest hammock (SIZEHAM) and species richness and diversity measures for MS is less clear. Because SIZEHAM included the hammock being sampled when point count sites were located within a hammock (Table
Species richness, species diversity, and effective number of species measures for YR responded in opposite ways to the amount of native hammock cover (PCT_HAM) observed for MS. Whereas PCT_HAM was the most important variable influencing presence of MS, this variable had a negative influence on the collective population of YR. This is because the majority of YR documented included species that are commonly associated with residential areas (Table
These results do not imply that there were no YR species that use or may even require native hammock cover. On the contrary, several YR species, such as the White-eyed Vireo and Carolina Wren (
As with MS, a negative relationship existed between SIZEHAM and D2HAM for species richness and diversity measures for YR. The negative relationship with SIZEHAM is consistent both with the observation that most YR species avoided hammocks and that detection rates were likely lower in larger hammocks due to dispersion and detection issues. Although detection rates were not quantified between YR and MS or between hammocks and residential areas, we do not believe this influences our conclusions. The negative relationship of both MS and YR (when analyzed simultaneously) with SIZEHAM does not alter interpretations of the positive response of MS and the negative response of YR to PCT_HAM, because YR species were much more abundant than MS and if YR were using hammocks to a similar or greater extent than MS, our data would have reflected this.
Although species richness and diversity measures for YR were negatively associated with PCT_HAM, we contend that the relationship between species diversity measures for YR and the distance to the nearest hammock (D2HAM) indicates most YR species benefit from the proximity of hammocks. Increased habitat diversity and foraging opportunities associated with native hammocks likely increased species diversity of YR in areas near hammocks, even if those species were more often observed in the residential landscape. This is because generalist species such as the Northern Mockingbird (
Conservation planning often prioritizes the protection of large, contiguous natural and seminatural areas to maximize benefits to biodiversity and sustain ecological processes and function [
Our results documented the importance of native hammock forest remnants to migratory birds in the Keys, including several species of conservation concern and provide empirical support for conservation efforts to protect remaining hammock habitat [
The authors thank the Islamorada Village of Islands for providing funding for this project. They also thank the staff and volunteers of Windley Key Fossil Reef Geological State Park and the staff at the Keys Marine Laboratory for their helpfulness during the fieldwork portion of their research.