THE CONDOR

AN INTERNATIONAL JOURNAL OF AVIAN BIOLOGY

May 1998

The Condor 100:201-217 0 The Cooper Ornithological Society 1998

Lsp- CJW- A QUANTITATIVE ANALYSIS OF#b&ER DIST UTION AND HABITATS OF KIRTLANDS’ WARBL

The Wilderness 900 17th Street, N. W., Washington, D.C. 20006, e-mail: [email protected]

DAVID S. LEE North Carolina State Museum of Natural Sciences, P.O. Box 29555, Raleigh, NC 27626

MARTHA WALSH-MCGEHEE Island Conservation Effort, Windwardside, Saba, Netherlands Antilles, West Indies

Abstract. We compiled and analyzed 101 accessiblereports of 194 individual Kirtland’s Warblers (Dendroica kirtlandii) from the Bahama Archipelago, 1841-1997. Most individuals were reportedfrom northernislands (88%), and most sightreports (84%) and specimen/banding records(76%) were on island groupsthat supportor formerly supportedopen woodlandsof Caribbeanpine (Pinus curilxzea). Where habitat descriptionswere provided, 60% mentioned specificallypines or pine understory.After analysesfor potentialbiases from misidentification in sight reports and unequaleffort acrossislands, we found no evidence to supportprevious claims that Kirtland’s Warblersprefer scrubor avoid pine habitats.Rather, based upon 1995- 1997 winter surveysusing acoustic broadcasts, K&land ’s Warblerswere detectedin pine wood- landsof Abaco and Grand Bahamamore frequentlythan expectedcompared to encounterrates generatedby a null model of random habitatuse. Two periodsof apparentdecline of the Kirt- land’s Warbler this century, and a modest populationincrease on the breeding groundssince 1990, occurredcontemporaneously with degradationand recovery, respectively,of the fire-de- pendentpine ecosystemin the northernBahamas. We recommenda rigorousre-evaluation of conservationpriorities now premisedlargely upon breeding-seasonlimitation. Key words: Bahama Islands, Caribbean pine, Dendroica kirtlandii, Kirtlands’ Warbler, Pinus caribaea,winter habitats.

INTRODUCTION Although it winters across widely-dispersed The striking feature of the endangeredKirtland ’s islands of the Bahama Archipelago (Mayfield Warbler (Dendroica kirtlandii) is a restricted 1992), the K&land’s Warbler has been extraor- distribution on both its breeding and wintering dinarily difficult to find and study there (Rada- grounds. Regarded as one of North America’s baugh 1974, Sykes 1989). Winter habitat was scarcestsongbirds, its rarity is usually attributed believed to consist of low, sparse, regenerating to scarce breeding habitat (fire-dependent jack vegetation (Mayfield 1992). The warbler was pine Pinus banksiana) and excessive brood par- thought to avoid woodlands of Caribbean pine asitism by the Brown-headed Cowbird Molo- (Pinus caribaea) (Mayfield 1996), a vegetation thus ater (Mayfield 1961, Walkinshaw 1972, type which possesses some of the structural Kelly and DeCapita 1982). characteristics of breeding habitat in Michigan (Radabaugh 1974). Despite few successful searches (Mayfield ’ Received 10 September 1997. Accepted 8 January 1972, Radabaugh 1974, Sykes 1989), the war- 1998. bler’s status outside the breeding season has

[2011 202 J. CHRISTOPHER HANEY ET AL. been a topic of ample speculation. It was as- TABLE 1. Distribution of wintering Kirtland’s War- serted that the winter habitats of the warbler blers from (islands and island groupspos- sessingor formerly possessingpine woodland indicat- have “. . . changed little over the last century” ed by *). Records which give only a general location, (Mayfield 1992) do “. . not appear to be such as “Bahama Islands,” not included (four reports threatened by human activities” (Mayfield of six individuals). 1996), and “. . . do not appear to be a problem” NO. (Sykes 1997). Management for this endangered NO. (% of indivi- specieshas been based largely on the belief that Island repons tOtal) duals winter habitats were stable: “since . . . the cli- Northern island groups mate and vegetation there [Bahamas] have 3 (3%) 3 (2%) changed little in centuries, we see no cause for Grand Bahama* 30 (30%) 59 (30%) alarm there at present” (Mayfield 1988). Con- Abaco* 10 (10%) 11 (6%) Berry Islands* 2 (2%) 4 (2%) sequently, active management of Kirtland’s War- Andros* 6 (6%) bler has been directed solely towards the breed- *a 20 (20%) 6: (3’::; ing grounds (Probst 1986, Kepler et al. 1996). Eleuthera 10 (10%) 18 (9%) In this study we synthesize winter reports of Cat 3 (3%) 3 (2%) the K&land’s Warbler accumulated since 1841, Subtotal 84 (83%) 170 (88%) and conduct the first quantitative evaluation of Southernisland groups the species’ habitat use and distribution during 0 (0%) 0 (0%) this season. We include recent unpublished re- Long 0 (0%) ports, and analyze irregularly-collected data for Rum Cay 21 (1%) 2: (iE; San Salvador 3 (3%) 6 (3%) biases that might influence apparent patterns of Crooked 1 (1%) 1 (

TABLE 2. Independentvariables used in regressionmodels that evaluatedwhich and how many factors might explain variability of total numbers of Kirtland’s Warblers recorded across the Bahama Islands. Islands with pines indicated with asterisk.

Human Human Distance to mainland Island area Island population sIzea population densitya Reporting effortb (k@ (km*) Bimini 1,638 70.3 14 161 23 Grand Bahama* 41,035 29.7 127 845 1,373 Abaco* 10,061 6.2 105 1,151 1,681 Berry Islands* 634 20.5 13 1,055 36 Andros* 8,755 1.6 85 918 5,957 New Providence*c 171,542 827.8 47 1,336 207 Eleuthera 10,524 20.5 21 1,650 518 Cat 1,678 4.2 2 2,004 389 Exuma 3,539 12.4 2 1,932 290 Long 3,107 5.4 3 2,318 596 Rum Cay 53 0.8 2 2,318 78 San Salvador 486 3.1 21 2,648 163 Crooked 423 1.9 8 2.673 181 Acklins 428 0.8 2 3;011 285 Mayaguana 308 1.2 1 2,882 285 Great Inagua 985 0.8 29 3.059 1.551 Little Inagua 0 0 0 3;180 ‘127 Caicos Bank*d 12,400 24.7 274 3,341 500

a Persons km-*; Se&y and Burrows 1982. b Numbers of rare or noteworthy bird records reported by field workers by island, 1947-1990; see text. c Including Paradise Island and Green Cay. d Turks and Caicos Islands; pine woodland only on North Caicos, Middle Caicos, and Pine Cay.

area with and without pine (Sealey and Burrows for the Kirtland’s Warbler have been attempted 1982) was used to construct a model that com- during winter, unequal effort could skew pat- pared observed to expected numbers of warblers terns of island and habitat use. We used regres- in tests of frequencies. All individual warblers sion models to explore whether total numbers of with specific winter localities (island) were used wintering warblers might be linked to effort. Be- in these analyses. cause visitors are likely to depend upon infra- structure such as roads, lodging facilities, and DATA EVALUATION transportation centers, we used island-specific To check for bias from potential misidentifica- total human population and population density tion and uncertain quality of sight reports, we (Table 2) as two proxies for effort. We also used conducted three exploratory analyses. Because a third proxy, reporting effort, based upon the an endemic, highly-distinctive race of Yellow- number of entries that highlighted bird species throated Warbler (Dendroica dominica javes- that were rare, unusual, or otherwise of special tens) is thought to be often confused with Kirt- interest from individual islands in the Bahamas land’s Warbler (Mayfield 1996, White 1996), we (boldfaced entries in Audubon Field-Notes and deleted all sight reports (n = 65) from the two American Birds, 1947-1990). islands where these two speciesco-occur (Grand Prior to constructing regression models, we Bahama and Abaco). We then ran a separate checked whether the variance of the enumerated analysis of warbler frequencies in remaining is- dependent variable (y; total warbler numbers) lands/island groups based upon presence or ab- could be stabilized (Snedecor and Co&ran sence of pine. We used a contingency chi-square 1980). Of transformations attempted (ln[y], test to examine whether sight reports were bi- ~og,&l, lnly + 11,log,& + 11,YO.~, LY + ll”% ased relative to specimen and banding records the best was 0, + 1)“.5,with the CV on y reduced in ascribing birds to pine and nonpine islands. from 177.2 to 77.7. Using the least-squares Finally, we conducted a test for frequency of MGLH program in SYSTAT (Wilkinson 1989), Kirtland’s Warblers on pine versus nonpine is- the dependent variable was then regressedindi- lands using only specimen and banding records. vidually on the three independent variables (x) As no systematic, archipelago-wide searches described above plus two geographic variables: 204 J. CHRISTOPHER HANEY ET AL. island area and distance of each island from the ed songs and calls of K&land’s Warblers in at- mainland of the southeasternUnited States. Dis- tempts to elicit observations during winter in tance from the U.S. mainland was measured pine habitats on Grand Bahama and Abaco. Vi- along a standardizedvector of 138” from eastern sual surveys were conducted 25 and 27 Novem- Florida. ber 1995 on Grand Bahama, and l-5 December To check whether all variables were needed 1995 on Abaco; acoustic and visual surveys in a model to predict total warbler numbers, we were conducted on 14-18 December 1996 on used the forward selection, stepwise regression Abaco, and 9-13 February 1997 on Grand Ba- option in the MGLH routine of SYSTAT (Wil- hama for a total of 18 survey-days. Surveyors kinson 1989) to identify a potential subset of generally worked in parties of two; two parties predictors (Dowdy and Wearden 1991). Alpha- were deployed on some days. to-enter and alpha-to-remove a variable were set While broadcasting calls and songs intermit- at 0.15. Three predictors were chosen: human tently from amplified recordings in all direc- population (+ = 0.61), human population den- tions, we walked slowly along roads or trails, sity (r2 = 0.85), and island distance (r2 = 0.89). stopping frequently about every 25-50 m, and A two-variable regression model was ultimately waiting up to lo-20 min to see whether any built with these predictors because the variable warblers responded. The open character of Ba- human population density was redundant with hamian pine woodland (Emlen 1977) allowed the variable human population. broadcasts to penetrate far laterally along the Discrepancies between estimated and ob- survey route; acoustic broadcasts were audible served values in regression models were used to to us at least 100 m away. No surveys were at- identify potential biases in effort for individual tempted during strong winds or rain. Surveys islands. Because Freeport, Grand Bahama, and were conducted in the morning and generally Nassau, New Providence, serve as major trans- completed within 4 hr. portation centers or final destinations for many After a warbler responded, the location was visitors, we hypothesized that more warbler re- marked with flagging. Total distance surveyed ports than expected might occur on these two was then measured directly with an automobile islands. Diagnostics from individual islands odometer, or pacing calibrated by an odometer. were examined for both the multivariate model After a warbler was detected, surveys were and those univariate regression models based moved to locations several km away to insure upon effort (human population size, human pop- independence. The product of transect length ulation density, reporting effort). and width gave the continuous area surveyed for Diagnostics included leverage statistics for a single warbler encounter. We used 150 m as detection of outliers and normal distributions in the effective transect width, the corridor within the independent variables, and Studentized re- which wintering warblers respond to acoustic siduals for detection of outliers in the dependent broadcasting (Graves 1996). variables (warbler numbers). Because testsof in- To examine whether Kirtland’s Warblers oc- ference using Studentized residuals were direc- curred in pine habitats more than expected by tional, we used one-tailed t-tests with n-m de- chance, we constructed a binomial model to test grees of freedom (n = total sample size; m = the null hypothesis of nonpreferential or random number of predictors in regression model, in- use of this habitat. The probability of finding a cluding the constant). We also used Cook’s F to warbler @) can be expressed as the product of examine regression coefficients (Velleman and the area censused (A) and expected density of Welsch 1981, Wilkinson 1989). The Cook test wintering warblers (B). Because this is one of statistic has m, n-m degrees of freedom and very few bird speciesfor which essentially com- combines leverage and Studentized residuals to plete censusesexist for the entire breeding pop- examine any influence of separate observations ulation, we estimated expected densities (B) for on estimates of the regression coefficients. each of the two winter seasonsby dividing the postbreeding size of the population by the area TRANSECT SURVEYS of the entire Bahama archipelago (14,600 km2; Because acoustic broadcastsincrease search ef- Sealey and Burrows 1982). ficiency compared to visual survey techniques Total postbreeding population sizes were es- (Wunderle 1992, Graves 1996), we used record- timated as 3,185 and 2,904 individuals for the WINTERING KIRTLAND’S WARBLERS 205

1995-1996 and 1996-1997 winters, respective- dominated (specimen records from Middle Cai- ly. These figures were obtained by adding the cos; sight reports from Middle Caicos and Pine number of females (based on 85% pairing suc- Cay: Sanderson 1982). cess; Probst and Hayes 1987) and young of the Most individuals (75%; n = 194) also were year (2.76 fledged young pairrl; Kelly and from northern islands that support Caribbean DeCapita 1982) to the annual census of singing pine (Table 1). Between 1841 and 1915, 78% of males (759 and 692 for 1995 and 1996, respec- all specimen records (n = 81 individuals linked tively). to specific islands) were obtained from pine- We assumedthat all warblers in the breeding dominated islands. More individual Kirtland’s population arrived and wintered only in the Ba- Warblers occurred on pine-dominated islands hamas (without mortality). This procedure in- than expected (x2, = 14.6, P < 0.001). Con- flates the true number of warblers that reach and versely, several of the larger islands where pines survive on the islands, leading to increased risk are absent accountedfor very few reports (Table of Type II error in subsequentanalyses. We were 1 and 2). most concerned, however, with making a false Although association with pine-dominated is- conclusion that Kirtland’s Warblers used pine lands by itself does not indicate that warblers habitat more than expected (Type I error). Thus, use this vegetation, Hundley (1967) remarked of estimated probabilities @) are best viewed as the Grand Bahama reports in the late 1950s and upper bounds on the likelihood of encountering 1960s: “almost all birds were seen in areas of a warbler during a winter survey. Under these Caribbean pine (Pinus caribaea) with an under- assumptions, maximum expected density (B) of story of poison wood (Metopium toxifencm) and warblers for the two winter seasons was 0.20 palmetto (Serenoa repens).” Only 2 of 52 re- and 0.22 warblers krn2, respectively. Each individual survey was then used to es- ports came from the western end of this island timate the likelihood of encountering a single where pine was absent. Although a few warblers warbler. Each survey was considered as a bi- have been observed in xeric scrub habitats in the nomial trial with the cumulative probability of southernpart of the Bahama Archipelago, where the outcome of multiple surveys (P) equal to the habitat descriptions for birds were provided (67 product of individual surveys that were either reports throughout the archipelago), 60% were successful@) or unsuccessful (4) in detecting a in pines or pine understory (Appendix 1). warbler. Statistical tests were considered signif- icant at P < 0.05 unless otherwise indicated; ANALYSES FOR IDENTIFICATION BIAS values listed are means + standard error. Despite reduced sample size from deleting all sight reports from Grand Bahama and Abaco, RESULTS the remaining reports of individual Kirtland’s DISTRIBUTION AND HABITATS Warblers exhibited a significant associationwith Only 3 of 107 winter reports originated from the remaining pine-dominated islands (x2, = 7.3, outside the Bahama Archipelago (2 sightings P < 0.01). Therefore, this analysis provided no from the northern Dominican Republic, 1 sight- evidence that misidentified D. d. jlavescens ac- ing from coastal Mexico). Of 104 Bahama re- counted for the association with pine-dominated ports, 3 could not be linked to a specific island islands. or island group. Most Bahama winter reports Similarly, we found no evidence that sight re- were from northern (88%), pine-dominated is- ports (rz = 88 and 17 on pine and nonpine is- lands (74%; Table 1). Kirtland’s Warblers oc- lands, respectively) were biased relative to the curred on each of the pine island groups in the proportions of specimen/banding records across northern archipelago: Grand Bahama, Abaco, pine (n = 68) and nonpine islands (n = 21; con- Berry Islands, Andros, and New Providence. Re- tingency x2, with continuity correction = 1.2, P ports from each of these five island/island = 0.27). Moreover, the warbler’s affinity for groups included specimen or banding records. pine-dominated islands was marginally signifi- Kirtland’s Warblers were recorded from the only cant when we analyzed the smaller sample con- other part of the archipelago with pine, the Turks sisting solely of specimen and banding records and Caicos, including those islands that are pine- (x2, = 3.2, P = 0.07). 206 J. CHRISTOPHER HANEY ET AL.

TABLE 3. Univariate regressionmodels (y = a + bx) used to evaluate variability in total numbersof Kirtland’s Warblersareported among 18 individual islands or island groups in the Bahama Archipelago, 1841-1997.

Independent vanable (x) y intercept (a) + SE Slope (b) Human population 2.13 ? 0.35 0.00004 0.61

a Dependent variable (y + 1)“.5, where y = total warbler numbers. b Observed significance levels for H, that b = 0.

WARBLER NUMBERS AND EFFORT for reporting effort also implicated this island Transformed total warbler numbers were signif- (t,5 = 2.42, P < 0.03). Grand Bahama had more icantly correlated with two proxies for effort: warblers than expected in the two-variable re- human population and human population density gression model as well (t15 = 3.88, P < 0.005). (Table 3). Transformed warbler numbers were Results for New Providence were inconsis- correlated marginally with reporting effort and tent. Contrary to expectations, the two-variable distance of island from the U.S. mainland (both regression model gave fewer warblers than ex- P = 0.06; Table 3). pected (t,, = -6.12, P < O.OOl), similar to the A two-variable regression model explained univariate model for human population (t,, = 67% of the variability in transformed warbler -6.87, P < 0.001). The model for human pop- numbers across islands (Table 4). Large toler- ulation density did not implicate New Provi- ances (> 0.92) indicated that the two predictor dence as having either more or fewer warblers variables were not intercorrelated (Wilkinson than expected (t,, = - 1.06, P > 0. lo), and the 1989). Human population size explained 61% of reporting effort model actually flagged this is- the variability in transformed total warbler num- land as having more warblers than predicted (t,, bers among islands (adjusted multiple ti = 0.58, = 3.69, P < 0.005). The only other island/island F I,16= 24.8, P < 0.001). Transformed warbler group identified as having disproportionatenum- numbers declined with increasing distance bers of warblers was the Caicos Bank, with the southeastwardthrough the Bahama Archipelago, model for reporting effort implicating this island although the amount of variability explained by group as having fewer reports than expected (t,, this predictor was low (20%; adjusted multiple = -3.05, P < 0.005). r;? = 0.15, F,,16= 4.0, P = 0.06). New Provi- dence had an especially large influence on the TRANSECT SURVEYS calculation of the regression coefficients in this We detected four Kirtland’s Warblers with, and model (Cook’s distance, F3,15= 70.7, P < 0.01). two without, using tape broadcasts. In contrast Univariate models based on human popula- to some other studies of wintering parulids tion and human population density identified (Graves 1996), none of the birds that were vi- Grand Bahama as having a disproportionately sually confirmed responded to acoustic broad- large number of the total warbler reports (Stu- castswith vocalizations of their own. Broadcasts dentized residuals, one-tailed t,, = 4.33 and did elicit vocal responsesfrom three birds hav- 5.15, respectively; both P -=c0.001). The model ing chip notes identical to Kirtland’s Warblers;

TABLE 4. Parametersfor two-variable multiple regressionmodel used to evaluate variability in total numbers of Kirtland’s Warblers”reported among 18 individual islandsor island groupsin the Bahama Archipelago, 184l- 1997.

Independent variable (x) Parameter coefficient 2 SE f Constant 3.37 t 0.80 4.19**b Human population (x1) 0.00004 ? 0.00001 4.61” Distance from mainland (.x2) -0.00094 2 0.00056 -1.69

a Dependent variable (y + 1)o.5, where y = total warbler numbers b Observed significance levels; * P < 0.001, ** P < 0.001. WINTERING KIRTLAND’S WARBLERS 207

TABLE 5. Test for nonpreferentialuse of winterhab- pine-dominated islands as having the majority of itat by Kirtland’s Warblersin the Bahamas.Outcomes winter reports. Although individual or collective reflectstatistical likelihood of findingthe numbersac- tually observedin pine habitaton GrandBahama and quality of sightings can be questioned, it is not Abacounder an assumptionof randomhabitat use. obvious why visual misidentification of Kirt- land’s Warblers should be limited to, or more Probability likely in, any one habitat. In any case, the ma- TIanSeCt AEXI of NO. length censused outcome, Cumulative jority of specimen records were certainly ob- Island/Yea? birds (W ww fi or g ’ probability, pd tamed from Dine-dominated islands. GB-95 1 3.00 0.45 0.10 0.10 Previous attempts to describe winter habitat AB-95 1 5.00 0.75 0.16 0.02 use of Kirtland’s Warblers either lacked quanti- AB-96-1 1 3.80 0.57 0.11 0.002 AB-96-2 1 10.00 1.50 0.30

West Indies open pine woodlands are found at height of 30 m with some trees as large as 0.75- sea level primarily in the Bahamas (Mirov 1967, 1.5 m in diameter (B&ton and Millspaugh 1962, Perry 1991); pine forest elsewhere occurs at Campbell 1978). Large-scale anthropogenic dis- high elevations where fire would have been less turbance of the pine ecosystembegan in the Ba- frequent due to moister conditions. Second, pa- hamas in the 1890s when the Kirtland’s Warbler leogeography suggests that during the Pleisto- was still readily found on its wintering grounds cene Kirtland’s Warblers were short-distancemi- (Appendix 1). At this time, Coker (1905) de- grants that bred closer to the Bahamas in the scribed the wood of the Caribbean pine as hav- nearby coastal plain of the southeasternUnited ing little commercial value due to its “rapid de- States (Mayfield 1988, Williams and Webb cay.” Prior to this period, turpentine and resin 1996). Extensive jack pine forest gradually mi- were extracted, but this localized industry grated north and west within the 10,000 years (which required living trees) was no longer ac- following Wisconsin glaciation (Mengel 1964). tive in the Bahamas by the turn of the century Pine forests have been present on the northern (Coker 1905). Pines were present on the Berry Bahamas since at least the late Pleistocene be- Islands until at least 1891 when Kirtland’s War- cause the fossil record contains several extant blers were originally reported from this island bird taxa that essentially are confined to pines group (Cory 1891, Gardiner and Brace 1889), (Brodkorb 1959, Olson and Hilgartner 1982, Lee but pine woodland was logged completely by et al. 1997). Over time the warbler came to ex- the early 20th century (Campbell 1978). ploit two fire-dependent pine ecosystems that Large-scale commercial exploitation of the became increasingly disjunct as changes in con- pine ecosystem started in 1905 with logging of tinental climate altered landscapes between the primary forest near Wilson City on Abaco Bahamas and their current breeding grounds. (Campbell 1978). This operation ran for 20 years. Little is known about impacts from lum- DISTURBANCE OF THE BAHAMIAN PINE bering during this period, but by 1943 nearly all ECOSYSTEM original forest had been cut, forcing the industry Despite repeated claims that interior habitats on to then turn to immature trees and shortrotations these islands were never altered appreciably for pulp (Campbell 1978). This initial period of (Mayfield 1983, 1988, 1992, 1996), major ecosystem manipulation (ca. 1900-1920) oc- changesin Bahamian land use have taken place. curred during the same time that Kirtland’s War- Moreover, these changes occurred while Kirt- blers apparently declined on their breeding land’s Warblers became scarce on both their grounds (Mayfield 1960). breeding and wintering grounds. For the archi- A second era of exploitation ran from the pelago at large, Byrne (1980:157) concluded 1950s through the early 1970s (Radabaugh that: 1974). Small pulpwood operations were carried out on Grand Bahama from about 1948 to 1955. . . the evidence recovered clearly shows that From 1956-1959, larger operations were estab- the Bahamas have not escaped the processes lished on Grand Bahama (Henry 1974). Lum- of change that have affected nearly all tropical bering removed 53,000 ha of pineland from this islands during the period of human settlement. 11 l,OOO-ha island. This was most of the pine In the comparatively short period of a thou- ecosystem as part of this island is covered in sand years [indigenous Arawak occupation mangrove or other vegetation, and pine wood- extended only from l,OOO-500 years BP], the land was always absent from the island’s west- Cat Island woodland has been drastically dis- em end. Lumbering also occurred on Abaco turbed. . .As a result of clearing, burning, se- where it continued there until 1970. On Andros, lective cutting, grazing, and browsing, sensi- lumbering startedin 1968 and apparently ceased tive [plant] species have become rare, and by 1973 (Radabaugh 1974). have survived as important members of the These operations severely degraded the orig- woodland only in remote, relatively undis- inal ecosystem. Radabaugh (1974) commented turbed areas. that the “. . .most significant environmental al- The original, native pine forest did not escape teration I observed-and probably the most sig- alteration (Nickrent et al. 1988). Primary forest nificant single change ever to occur in the Ba- of Caribbean pine once achieved a maximum hamas-was the lumbering of the Caribbean 210 J. CHRISTOPHER HANEY ET AL pines.” C. R. Mason reported that where once 1960), the breeding range is roughly 35% larger there was unbroken pine woodland “most of the than the area of the entire Bahama archipelago, land is cut over, burned over, much of it being and 10 times larger than the area of pine wood- planted in cane” (Audubon Field-Notes 22:30). land (1,920-2,042 km*; Allan 1986, N. Sealey, Ring et al. (1979) described how except for a pers. comm.). Thus, a more geographically-con- small 1,620-ha tract on Little Abaco and a tracted winter range could be even less able than smaller area at the southern end of Great Abaco, the breeding grounds to absorb extensive habitat all pines had been removed by 19761977. Rad- modification. abaugh (1974) estimated that 200 km* of Abaco Cowbird control on the breeding grounds, al- was completely treeless. One 17,820-ha tract of though arresting the warbler’s decline and rais- logged-over land was planted in sugar cane ing productivity (Robinson et al. 1995), failed to (Snyder et al. 1982), an area equivalent to 11% initiate an immediate increase in the population of Great and Little Abaco combined. (James and McCulloch 1995). In general, strong Subsequent regeneration of pine was uneven inferences about population trends of Neotropi- at best, poor to nonexistent at worst. Snyder et cal migrants are made difficult from confound- al. (1982) noted that hurricanes on Abaco lev- ing events on both breeding and wintering eled most residual seed trees and damaged oth- grounds (Latta and Baltz 1997). We extend this ers sufficiently that they were later lost to insect caution specifically to the Kirtland’s Warbler, outbreaks. Moreover, the large amounts of slash and emphasize that potential causes impacting produced intense and extensive fires. Radabaugh populations on the wintering grounds also were (1974:380) observed unattended fires burning coincident in time with the warbler’s general de- for days on Grand Bahama and Andros, noting cline. The initial decline is attributed usually to that: reduction in breeding range after a particularly large fire had earlier created extensive habitat pulpwood operations at least temporarily re- (ca. 500,000 ha) in 1871 (Mayfield 1993). But move, and sometimes completely destroy, the this decline also corresponds to land-use Caribbean pine ecosystemover vast areas . . . changes in the Bahamas, including commercial- to the extent that the Kirtland’s Warbler, as a scale logging. Notably, Maynard seemedto have species,relies on pinelands in winter, lumber- had little difficulty in collecting the warbler in ing could well have been detrimental to the the Bahamas as late as 1915 (Appendix l), long point of having contributed to the recent de- after (44 years) the extensive breeding habitat cline in numbers. noted above would have lost its suitability (6- This later period of ecosystem manipulation 25 years postfire: DeGraaf and Rappole 1995). (1956-1973) encompassesthe precipitous 60% An upswing in numbers of warblers since decline in warblers observed between the 1961 about 1990 occurred after a period in which Ba- and 1971 breeding censuses. hamian pine woodland recovered from the com- pressed period of short-rotation logging in the CONSERVATION IMPLICATIONS 1970s. Pines regenerated on some sites where Becausebreeding or wintering seasonconditions cutting was severe (Abaco) and matured on can simultaneously influence bird populations thinned sites (Emlen’s [1977] study sites on (Sherry and Holmes 1995), factors during either Grand Bahama). Normal fire regimes also may or each period could conceivably limit recovery. be returning now, as we saw evidence of low- Rappole and McDonald (1994) list predictions intensity fire in virtually all areas of Abaco and that might identify whether winter factors are Grand Bahama that we surveyed. important for Neotropical migrants. One such Habitat loss, incompatible silviculture, and al- prediction is that breeding habitat of Kirtland’s tered fire regimes pose both direct and indirect Warbler should appear filled if it is breeding- threats to birds that rely on pine ecosystems season limited. In fact, “. . . some [breeding] (Jackson 1986, Rudolph and Conner 1996, tracts that appear promising are not occupied” James et al. 1997). Declines of endemic taxa (Mayfield 1992). Failure to occupy even all op- confined to pines in this archipelago (Allen timal habitat (Nelson and Buech 1996) weakens 1996) occurred during the periods of habitat support for strict breeding season limitation. modification. A subspecies of Brown-headed Furthermore, at some 21,760 km2 (Mayfield Nuthatch (Sitta pusilla insularis) is now much WINTERING KIRTLAND’S WARBLERS 211 reduced (Smith and Smith 1994). The Brace’s BANGS,0. 1900. Notes on a collection of Bahama Emerald (Chlorostilbon brucei) is gone from birds. Auk 17:283-293. BLANCHARD,D. 1965. Kirtland’s Warbler in winter on New Providence (Olson and Hilgartner 1982), Grand Bahama Island. Jack-Pine Warbler 43:39- and an endemic race of the West Indian Wood- 42. pecker (Centurus superciliaris) has disappeared BGHNING-GAESE,K., M. L. TAPER,AND J. H. BROWN. from Grand Bahama (Emlen 1977, Smith and 1993. Are declines in North American insectivo- Smith 1994). Bahamian pine forest is lost at high rous songbirds due to causes on the breeding range? Conserv. Biol. 7:7&86. rates and is the least protected category of hab- BOND,J. 1951. First supplement to the checklist of itat types in Latin America and the Caribbean birds of the West Indies (1950). Acad. Nat. Sci. (Dinerstein et al. 1995). Philadelohia. Philadelnhia. PA. The winter stage of the warbler’s annual cycle BOND,J. 1957. Second su’pplementto the checklist of has been mostly ignored compared to protection birds of the West Indies (1956). Acad. Nat. Sci. Philadelphia, Philadelphia, PA. efforts on the breeding grounds. At a minimum, BOND, J. 1968. Thirteenth supplementto the checklist we believe that maintaining the current view of of birds of the West Indies (1956). Acad. Nat. Sci. a population that is strictly breeding season-lim- Philadelphia, Philadelphia, PA. ited (Sykes 1997) carries great risk. Our analy- BONHOTE,J. L. 1903. On a collection of birds from ses show that open canopy pine forest on the the northern islandsof the Bahama groups.Ibis 3: 273-315. large islands of the northern Bahamas provides BRITON, N. L., AND C. E MILLSPALJGH.1962. The extensive natural habitat for wintering Kirtland’s Bahama flora. Hafner, New York. Warblers. Winter habitat should be included in BRODKORB,I? 1959. Pleistocenebirds from New Prov- planning for the long-term conservation of this idence Island, Bahamas. Bull. Florida State Mus. endangered Neotropical migrant, otherwise, cur- 4:349-371. BUDEN,D. W. 1987. The birds of Cat Island, Baha- rent management efforts could be compromised. mas. Wilson Bull. 99:579-600. BUDEN,D. W. 1990. The birds of Rum Cay, Bahama ACKNOWLEDGMENTS Islands. Wilson Bull. 102:45l-468. This studywas facilitatedby a partnershipamong the BUDEN,D. W. 1992. The birds of the , Ba- NorthCarolina State Museum of NaturalSciences, the hama Islands. Wilson Bull. 104:674-698. BahamasNational Trust, College of the Bahamas,and BUDEN,D. W., AND A. SPRUNTIV. 1993. Additional the Bahama Department of Agriculture under the In- observationson the birds of the Exumas, Bahama ternational Aves de las Americas/Partners-in-Flight Islands. Wilson Bull. 105:514-518. Program. The American Bird Conservancy and Na- BYRNE,R. 1980. Man and the variable vulnerability tional Audubon Society provided partial support for of island life: a study of recent vegetation change the 1996-1997 surveys on Abaco and Grand Bahama. in the Bahamas.Atoll Res. Bull. No. 240, Smith- C. Faanes, J. Gerwin, R. Gnam, P. W. Smith, A. son. Inst., Washington,DC. Sprunt, and G. Woolfenden provided habitat informa- CAMPBELL,D. G. 1978. The ephemeral islands: a nat- tion on warblers they encountered.K. and R. Oliver, ural .Macmillan, London. M. DeCapita, and I! Huber assisted with the 1996- CHALLINOR,D., JR. 1962. Recent sight recordsof Kirt- 1997 field surveys on Grand Bahama. N. Sealey sup- land’s Warbler in the Bahama Islands. Wilson plied data on area of pine forest in the Bahamas, and Bull. 74:290. D. Pashley supplied a copy of his unpublishedbibli- CHAPMAN,E M. 1898. Kirtland’s Warbler (Dendroica ography on Kirtland’s Warbler. Staff at the Smithson- kirtlandii). Auk 15:289-293. ian Institution libraries helped us with locating many CHAPMAN,E M. 1899. Further notes on Dendroica obscure sources.Comments by D. Buden, S. Busack, kirtlandii. Auk 16:81. E Gill, S. Senner, T. White, and two anonymousre- CHAPMAN,E M. 1908. Camps and cruises of an or- viewers improved earlier versions of this manuscript. nithologist. D. Appleton, New York. CLENCH,M. H. 1978. Search ends: a Kirtland’s at last. LITERATURE CITED Bull. Audubon Sot. West. Pennsylvania42:8. ALLAN, T G. 1986. Management plan for the pine COKER,W. C. 1905. Vegetation of the Bahama Is- forests of the Bahamas.UTF/BHA BHA Consul- lands. MacMillan, London. tancy Rep. No. 2. Food and Agriculture Organi- CORY, C. B. 1879. Capture of K&land’s Warbler zation of the United Nations, Rome. (Dendroicu kirtlandii) in the Bahama Islands. ALLEN,P E. 1996. Breeding biology and natural his- Bull. Nuttall Ornithol. Club 4: 118. tory of the Bahama Swallow. Wilson Bull. 108: CORY,C. B. 1886. The birds of the West Indies, in- 480-495. cluding the Bahamas Islands, the Greater and BAIRD, S. E 1865. Review of American birds in the Lesser Antilles, excepting the islands of Tobago museum of the Smithsonian Institution, Pt. 1, and Trinidad. Auk 3: l-59. 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