Site Fidelity and Ephemeral Habitat Occupancy: Northern Waterthrush Use of Puerto Rican Black Mangroves during the Nonbreeding Season

7 Pages·2002·5 MB·English

by  Leonard Reitsma

Wilson Bull., 1 14(1), 2002, pp. 99-105
SITE FIDELITY AND EPHEMERAL HABITAT OCCUPANCY:
NORTHERN WATERTHRUSH USE OF PUERTO RICAN BLACK
MANGROVES DURING THE NONBREEDING SEASON
LEONARD REITSMA,' 24) PAMELA HUNT,'-^ SHERMAN L. BURSON, ^ AND
BENJAMIN B. STEELE'
—
ABSTRACT. We studied thedispersion ofNorthern Waterthrushes(Seiurusnovahoracensis) insouthwestern
Puerto Rico during four nonbreeding seasons, 1996-1999. Densities were high (up to 13 birds/ha) on a 3-ha
mature black mangrove (Avicennia germinans) study plot, but were significantly lower during periods of high
water levels. Individuals exhibited site fidelity within and between seasons. Feeding areas were small (mean =
0.074 ha ± 0.041 SD) and there was considerable overlap tolerated among conspecifics. Waterthrush density
decreased when water submerged their primary foraging substrate: woody debris and pneumatophores. Inter-
annual returns were similar to other Neotropical migrants (mean = 50%) but site persistence was low due to
periodic flooding. In September 1998, hurricane Georges flooded the plot and blew down >90% of the black
mangrove trees. This drastic habitat alteration was followed by adrastic decline in waterthrushes usingthe study
area. Individuals left feeding areas for overnight roost sites in red mangroves (Rhizophora mangle). This latter
finding, coupled with site fidelity and high return rates concurrent with low site persistence, suggests that
waterthrushes exhibit high plasticity in their use of habitat during the nonbreeding season, but may rely upon
mangroves for overwinter survival. Received 15 May 2001, accepted 13 March 2002.
Nearctic-Neotropical migratory passerines Waide 1994). Already, forest cover is esti-
spend over half of each year in the tropics, mated to have declined to about 21% ofisland
commonly returning to the same sites (Faa- land area in the Caribbean (Wunderle and
borg and Arendt 1984, Lynch et al. 1985, Waide 1994).
Kricher and Davis 1986, Holmes et al. 1989, Mangrove forests have some of the highest
Winkeret al. 1990). This realization has likely abundances of overwintering migrants in the
influenced the increase in studies that focus Caribbean (Arendt 1992, Lefebvre et al. 1992,
on winter habitat loss and its effect on popu- Robbins et al. 1992, Sliwa and Sherry 1992,
lations of migrants. While almost all migrants Wunderle and Waide 1993). However, few de-
are territorial during the breeding season, win- tailed population studies have been conducted
ter habitat use varies widely between species in mangroves (but see Holmes and Sherry
and many species’ use ofhabitat is still poorly 1992; Lefebvre et al. 1992, 1994; Lefebvre
understood. Population studies recently have and Poulin 1996; Marra and Holmes 2001).
demonstrated that optimal nonbreeding habitat Several studies have used marked individuals
may be limiting, at least for some species on the wintering grounds to quantify overwin-
(Rappole et al. 1989, Marra et al. 1998), thus ter site persistence, annual return rates, and
the high rate ofdeforestation in Middle Amer- dispersion (Winker et al. 1990, Holmes and
ica and the Caribbean potentially will have a Sherry 1992, Mabey and Morton 1992, Stai-
great impact on migrant bird populations cer 1992, Wunderle 1992, Marra et al. 1998).
(Rappole and Powell 1986, Wunderle and Some migrants in mangroves defend territo-
ries (Holmes et al. 1989, Rappole et al. 1989,
' New England Inst, for Landscape Ecology, Box Mabey and Morton 1992).
38-H, RR2, Canaan, NH 03741, USA.
The Northern Waterthrush {Seiurus nova-
2Current address: Dept, of Natural Sciences, Plym-
outh State College, Plymouth, NH 03264, USA. horacensis) has been documented as the most
^Current address: Audubon Society ofNew Hamp- abundant migrant passerine in some man-
shire, 3 Silk Earm Rd., Concord, NH 03301, USA. groves (Lefebvre et al. 1992, Wunderle and
Current address: P.O. Box 47, Denali Park, AK Waide 1993). Lefebrve et al. (1994) and Le-
99755, USA. febvre and Poulin (1996) concluded this spe-
^Current address: Dept, ofNatural Sciences,Colby-
Sawyer College, New London, NH 03257, USA. cies was not territorial in either Venezuelan or
^Corresponding author; E-mail: Panamanian mangroves, respectively, in con-
[email protected] trast to Schwartz’s (1964) reports of territori-
99
100 THE WILSON BULLETIN • Vol. 114, No. 1, March 2002
ality in this species within an irrigated botan- We collected data in January during the 1995-1996
ical garden in Venezuela. nonbreeding season (September through early April),
We monitored the use of a mature black and in October, January, and March for the following
mangrove (Avicermia genninans) forest by a n3etyse,arasn.dWcoelocrabptaunrdeeddNeoarcthhebirrnd.WWateermteharsuusrheesdwienigmhits,t
marked population of Northern Waterthrushes fat (0-4 visual index of interfurcular fat), and unflat-
over four nonbreeding seasons to determine tened wingchord. Duringthe last2 years,wecollected
whether this species (1) exhibits site fidelity 5 |xl of blood from the brachial vein of birds to sex
in this habitat, and (2) responds to changes in individuals ofthis monochromatic species. We used a
habitat suitability within and between seasons. combination of PCR and electophoretic detection of
Natural changes that occurred during our diagnostic protein bands to determine sex (Griffiths et
al. 1996) for some individuals, and nonoverlapping
study allowed us to document the degree of wing chord length distinctions in others (>78 mm for
plasticity that this species exhibits in response males, <71 mm for females; Pyle et al. 1987).
to both short term and long term habitat We systematically searched the plot for Northern
changes. Waterthrushes during each time period, and locations
and movements of banded and unbanded birds were
STUDY AREA AND METHODS recorded. A bird was considered a resident if it was
We mapped the spacing pattern, and measured den- relocated >4 days in the same area in one time period
sity and site persistence ofNorthern Waterthrushes on of a single season. All observations were compiled
a 3-ha plot within a mature black mangrove forest. during each trip to produce minimum activity ranges,
This site (18°01' N, 67° 10' W) was located on the which were the minimum convex polygons encom-
Boqueron Bird Refuge, a 182-ha reserve located 8 km passing all observations ofindividual birds (Holmeset
south of Cabo Rojo in southwestern Puerto Rico and al. 1989). We refer to these minimum activity ranges
managed by the Puerto Rican Dept, of Natural Re- as feeding areas ratherthan territoriesbecause individ-
sources. This forest was separated from a red man- uals did not aggressively exclude conspecifics, but
grove (Rizophora mangle) stand and open lagoons by they did exhibit within and between season site fidel-
a manmade dike. The plot had a mean canopy height ity, and they actively fed in these restricted areas. In-
owfer1e2bmlaacnkdmaanmgeraonveosf.25T6hetrfeeosr/ehsat,fnleoaorrlwyaasllaofcwohmibcih- tueproannnuraelsirgehttuirnngsrataesndanrdecsaiptetupreerss.istWeenceinwveersetibgaasteedd
nation ofshallow water (<25% cover when not flood- movement ofbirds toward and away from the plot us-
edde)b,risl.eafWalitteterrt,hmraunshgersovfeorpangeeudmaptroepdhoomriensa,ntalnyd ownootdhye iinngg msiesatsonne.ttAinng8d0ur-i1n2g0alml tmhirsete tniemteslaonfetwhaesnoonpberreaetde-d
forest floor, but also searched for food on woody de- for 4 h after dawn and 4 h preceding dusk on the dike
bris, upturned root masses, and in black mangrove along the west edge of the plot. Travel direction was
recorded for each bird captured.
trees.
Periodic flooding of the plot occurred throughout We used simple regression to correlate water depth
our study as a result of variations in rainfall between on the plot with bird density, and to correlate density
September and December. We measured water depth with the amount of overlap in feeding areas. Overlap
cbheagninnenlinagdjianceJnatnutaortyhe19pl9o7tuasnidngcaaligbraautgeed tphleaccehdaninnela twwaosqouranmtoifrieedfaesedtihnegpearrceeanstocvoevrelrapopfetdh.epWleotuinsewdhicchhi
depth to the plot water depth. Eor time periods prior square analysis to test for differences in travel direc-
tothe placementofthegauge inthe field, weestimated tion of birds into the mist net lane after dawn com-
pthneeuwmaatteroplheovrelessbayndcopmepracreintngoptheenrwealatteirveceoxveprosounrethoef wpairnegd ctohobredforraetidousskw.erSeeasaonnaallyzcehdanugseisnginAbNodOyVmAasst/o
plot. March 1997 and 1998 and January 1998 were measure weight loss during the nonbreeding season.
similar in water level to the conditions prior to instal- To obtain an adequate sample size for analysis of all
ling the gauge, and measurements during these three three time periods ofeach season, the sample included
intervals allowed reasonably accurate estimates ofthe all Northern Waterthrushes caught on the plot and on
Gtewoorgpeesr,iotdhsepmraenvigoruosvetofoirnestsatllhaatdiona.clBoesfeodrecaHnuorpryicaannde thhaevedifkeeedaidnjgacaernetastoonthetheploptl,ot.moWset oaflsowhuiscehddaidr-tneostt
little foliage below 2.5 m. The hurricane dramatically to analyze differences in body mass/wing chord ratios
altered this habitat in September 1998, leaving <10% for resident birds on the plot during October and Jan-
of the trees standing. The plot was still flooded 6 uary, for which we had adequate sample sizes.
months after the hurricane, and little vegetative re-
growth had occurred. We estimated the water levels RESULTS
for the periods after the hunicane by comparing the The number of Northern Waterthrushes on
height of water on prominent standing trees and other
unaltered features on and around the plot to flooded the 3-ha study plot ranged from 39 in October
periods when the gauge was in place, such as January 1996 to 0 in March 1999 (Eig. 1). Eeeding
and October 1997. areas were small (mean = 0.074 ha ± 0.041
Reitsma et cil. • NORTHERN WATERTHRUSHES IN PUERTO RICX3 101
January 1996
N=23
I 1 1
100m
£
Year -^80
One £60;
V
North i>t)
October 1996 January 1997 March 1997
N=39 N=19 N=21
March 1998
N=10
October 1998 January 1999 March 1999
N=8 N=2 N=0
EIG. 1. Eeeding areas of Northern Waterthrushes on a 3-ha mature black mangrove study plot at the Bo-
queron Bird Refuge in southwestern Puerto Rico during four nonbreeding seasons. Each polygon encloses all
the observations of individually color-marked birds that were resighted >4 times on the plot during each des-
ignated time period. The number ofmapped birds and the mean water depth ofthe plot (WD, in cm) is shown.
The entire plot is covered with water when WD > 25 cm. The west side of the plot is bounded by a dike.
Hurricane Georges drastically altered the structure ofthis forest plot in September 1998just prior to YearEour.
By March 1999, no resident birds remained.
SD, n = 158). During times of high density, January 1997 with a corresponding >50% de-
t=her2e6.w4a9,s gPrea=ter0.o0v0e0r9l,apFin=fe0e.d7i6n8g).areDaesns(iFt^y§ ccluirnreedinprdieonrsittoy O(cFitgo.be1r). 1F9l9o7odianngd aOlcstooboecr-
fluctuated widely within and between seasons 1998 and was associated with much lower
and was negatively correlated with water densities compared to October 1996. The low-
depth (F,j = 5.403, P = 0.049, F = 0.403). est densities occurred after severe hurricane
Flooding occurred between October 1996 and damage (October, January, and March of the
102 THE WILSON BULLETIN • Vol. 114, No. 1, March 2002
fourth season). Overall site persistence was DNA and 13 were males (28.9%), a propor-
low (42%) and varied from one interval to tion consistent with that of the residents.
another.
DISCUSSION
Of 23 Northern Waterthrushes with well-
documented feeding areas on the plot during When not flooded, this mature black man-
January of 1996, 12 (52%) returned the fol- grove forest had among the highest density
lowing season and five (22%) returned again (13 birds/ha) of marked resident birds of any
the next season. Return rates were lower be- previously recorded Neotropical migrant pop-
tween the second and third seasons of this ulation (but see Marra and Holmes 2001, who
study (8 of 26 birds, 31%) and lower still be- reported 15 American Redstarts, Setophaga
tween the third and fourth seasons (2 of 14 ruticilla, per ha during fall and 12/ha during
birds, 14%). Of63 well-mapped birds overthe spring). However, the conditions of this and
4-year study, 21 (33% of the original cohort) other habitats (PH unpubl. data) used by
had feeding areas in >2 consecutive years and Northern Waterthrushes were not stable. On
five (7.9% of the original cohort) had feeding the black mangrove plot, densities were in-
areas in three consecutive years. One of the versely associated with water level. A similar
3-year occupants was recaptured the fourth pattern was documented in other habitats in
season but did not have a known feeding area southwestern Puerto Rico (LR unpubl. data).
on the plot. Moist ground appears to be the most suitable
Waterthrushes lost mass throughout the sea- feeding substrate for waterthrushes in black
son. The body mass/wing chord ratio of all mangroves, but standing water that submerges
waterthrushes, including transients, decreased pneumatophore tips precludes their ability to
throughout the nonbreeding season from Oc- forage on the ground. Woody debris and dead
tober (mean - 0.23 g/mm ± 0.02 SD, n trunks remain useable when pneumatophores
158) to January (0.22 ± 0.01 SD, n = 102) are submerged, but the majority of water-
and then further in March (0.21 ± 0.02 SD, n thrushes we observed foraging were walking
- 9; ^2,226 - 4.71, P = 0.01). For resident on the ground among the pneumatophores.
birds, we had adequate sample sizes to com- The linear dispersion of individuals along the
pare only October to January, and the pattern drier dike during periods of flooding (Fig. 1:
was consistent (October mean == 0.23 ± 0.02 October 1997 and March 1998) provides fur-
SD, n = 23, and January mean = 0.22 ± 0.02 ther evidence for the importance of water lev-
SD, n = 41- t = 1.998, df = 6H, P = 0.05). el. These individuals had moist ground sub-
Birds consistently moved across the dike strate for foraging, allowing them to persist
from the red mangrove side in the morning along the edge of the plot.
and from the black mangrove side at dusk (/? The response of Northern Waterthrushes to
- 100, = 37.37, df = \, P < 0.001). Of Hurricane Georges was marked. The hurricane
the birds captured in the morning, 64% (/? = covered the plot with an estimated mean of
45) were going from red to black mangrove. 0.75 m of water and destroyed most of the
Of the birds captured in the evening, 89% (/? canopy trees. Even though many birds were
= 55) were going from black to red man- caught in nets on the dike and on the plot
grove. within 3 weeks after the hurricane, these birds
We determined the sex of 25 resident birds, likely were spending most oftheir time offthe
10 using blood DNA and 15 using wing chord plot because only 2 of 48 caught on or near
lengths. Genetic analysis of blood showed no the plot were resighted. Bird activity on the
sex bias (6 of 10 sexed were males). The ma- plot declined during the 2 weeks following the
jority (14 of 15, 93%) of all birds sexed by hurricane, October 6-22, 1998, and was mark-
wing chord length were females. Therefore, 7 edly lower still in January and March 1999.
of 25 birds of known gender with well- This probably was due to a lack of preferred
mapped feeding areas on the plot were male foraging substrate because ofthe flooding and
(28%). The sample sizes were too small to the disappearance of the canopy, which pro-
compare sex ratios within or between seasons. vided shade (see Schwartz 1964 for proposed
An additional 45 transients caught on or ad- minimum habitat requirements).
jacent to the plot were sexed using blood The fact that abundance on the plot varied
Reitsnui et al. • NORTHERN WATERTHRUSHES IN PUERTO RICO 103
SO greatly during each winter (19 to 39, 10 to the nonbreeding season among a local popu-
21, and 0 to 8) demonstrates the ability, and lation of Northern Waterthrushes within an ur-
perhaps the necessity ofwaterthrushes to shift ban park in Venezuela, but this territorial de-
their daytime feeding areas. Although most of fense may have been in response to artificial
these birds were found repeatedly on one ground moisture supplied by irrigation. Al-
small part of the plot while they were resi- though most wintering migrants are territorial
dents, they went elsewhere when water cov- or occur in mixed species flocks, species with
ered the foraging substrate and they presum- overlapping home ranges have been reported
ably found suitable habitat elsewhere. Individ- elsewhere in Puerto Rico (Staicer 1992).
uals banded during October sometimes were The consistent predictable movement of in-
not present during January, but were seen on dividuals from black to red mangrove for
the plot in March, indicating that the disap- overnight roosting was further supported by a
pearance of birds from the plot during high minimal amount of radio telemetry (LR un-
water did not represent mortality but move- publ. data). Individuals that fed in the black
ment to other areas. This is consistent with the mangroves traveled to the red mangroves
lack of season-long residence by waterthrush- across the dike in the evening and then back
es in Panamanian mangroves (Lefebrve and to the black mangroves the next morning. This
Poulin 1996). In Panama, waterthrushes ap- use of red mangroves was further corroborat-
peared to be tracking food abundance, and the ed by more detailed studies at a site 6 km to
authors suggested that the movement they the south and a site on the east side of Puerto
documented may represent a broader pattern Rico (LR unpubl. data).
of midwinter migration for at least some spe- Body mass to wing chord ratios declined
cies of Neotropical migrants. The large num- throughout the nonbreeding season from Oc-
ber of transient birds captured on or near the tober to March. This analysis was consistent
plot and never resighted suggests that many for resident birds and for residents and tran-
individuals simply moved through the plot. sients combined. The pattern is similar to that
Recent evidence from telemetry suggests that which occurred in American Redstarts in Ja-
many “transients” move considerable distanc- maica (Marra et al. 1998) and Belize (S. Baird
es through many habitat types en route from unpubl. data). Body condition might be ex-
regular feeding areas to roost sites (LR un- pected to decline given the general drying
publ. data). trend in most of Puerto Rico, and especially
Although many species of Neotropical mi- in the southwest, from January to the end of
grants are territorial during the nonbreeding March, which often reduces arthropod abun-
season (Lynch et al. 1985, Holmes et al. 1989, dance.
Rappole et al. 1989, Marra et al. 1998), North- Individuals of both sexes had feeding areas
ern Waterthrushes are not when they occupy on the plot. Birds that moved through the plot
mangroves (see also Lefebvre et al. 1994 and and those that remained on it to feed both
Lefebvre and Poulin 1996). Two to five indi- showed similar sex ratios of three females to
vidual feeding areas often overlapped, and one male. Despite the fact that the majority
overlap increased significantly with increasing (70%) of captured birds were not sexed and
density on the plot. Two to three individuals therefore the complete demographic makeup
occasionally were observed <2 m from each of this population was not known, our data
other, and when flushed they often would fly suggest that waterthrushes do not appear to
in the same direction. Some individuals did, sexually segregate by habitat, at least to the
however, exhibit site fidelity to feeding areas, same degree as some other migrant warblers
returning to the same specific areas on the plot such as the American Redstart (Marra and
on successive days and in successive years. Holmes 2001, Parrish and Sherry 1994). We
Return rates were highest from first to second conclude that both sexes were residents on the
year (52%), and the lower rates in subsequent plot for the duration of our monitoring, but
years may have been influenced by the higher we do not know the precise sex ratio at any
incidence of flooding from 1997 through single interval of our study.
1998. Schwartz (1964) documented classic The high density ofNorthern Waterthrushes
territorial behavior during the second half of documented in black mangroves in this study
104 THE WILSON BULLETIN • Vol. 114, No. 1, March 2002
and others (e.g., Lefebvre et al. 1994) indi- sizes and philopatry ofwinterresidentwarblersin
cates the importance of this habitat to sustain- Puerto Rico. J. Field Ornithol. 55:376-378.
ing waterthrush populations during the non- Griffiidtehnst,ifiRc.a,tiSo.nDinaabinr,dsaunsdinCg.twDiojCksHtrDa.gen1e9s9.6.PrSoecx.
breeding season. This habitat is subject to R. Soc. Lond. Sen B 263:1251-1256.
considerable short term change, mostly due to Holmes, R. T. and T. W. Sherry. 1992. Site fidelity
changes in water levels, but also due to chang- of migratory warblers in temperate breeding and
es in food abundance (Lefebvre and Poulin Neotropical wintering areas: implications forpop-
1996). This might particularly influence its ulation dynamics, habitat selection, and conser-
suitability for a ground forager such as the vation. Pp. 563-578 in Ecology and conservation
Northern Waterthrush. As a result. Northern of Neotropical migrant landbirds (J. M. Hagan,
III, and D. W. Johnston, Eds.). Smithsonian Inst.
Waterthrushes must be capable of changing
Press, Washington, D.C.
locations over the course of any single non- Holmes, R. T, T. W. Sherry, and L. Reitsma. 1989.
breeding season, and other locations and hab- Population structure, territoriality, and overwinter
itats may be essential to their survival. Lefeb- survival oftwo migrant warbler species in Jamai-
vre and Poulin (1996) suggest that migrant ca. Condor 91:545-561.
dwellers of mangroves may regularly migrate Kricher,j. C. andW. E. Davis,Jr. 1986. Returnsand
winter-site fidelity of North American migrants
into and out of habitat patches, tracking the banded in Belize, Central America. J. Field Or-
phenology of arthropod food in each. In our nithol. 57:48-52.
study, the changes in habitat quality resulting Lefebvre, G. and B. Poulin. 1996. Seasonal abun-
from flooding also may eliminate the benefits dance ofmigrant birds and food resources in Pan-
of territorial behavior in favor of more oppor- amanian mangrove forests. Wilson Bull. 108:748-
759.
tunistic occupation of suitable feeding sites.
Lefebvre,G., B. Poulin,andR. McNeil. 1992. Abun-
Despite the documented within season mo-
dance, feeding behavior, and body condition of
bility of this species, the high densities in Nearctic warblers wintering in Venezuelan man-
mangroves, the return to mangroves when this groves. Wilson Bull. 104:400-412.
habitat becomes suitable, and the daily move- Lefebvre, G., B. Poulin, and R. McNeil. 1994. Spa-
ment back into red mangroves to roost, all un- tial andsocial behaviourofNearctic warblerswin-
derscore the importance of mangrove habitats tering in Venezuelan mangroves. Can. J. Zool. 72:
to Northern Waterthrushes. The rapid human 757-764.
destruction of mangroves has the potential to LyncVho,oRJ.T.E,19E8.5.S.HaMboitrattons,egraengdatiMo.n Eb.etVweaenn dtehre
cause declines in the species’ population. sexes ofwintering Hooded Warblers (Wilsoniaci-
ACKNOWLEDGMENTS trina). Auk 102:714-721.
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This research was supported by acooperative agree- and territorial behavior of wintering Kentucky
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Inst, for Tropical Forestry, and by the New England conservation of Neotropical migrant landbirds (J.
Inst, for Landscape Ecology. We thank M. Baltz for M. Hagan, III and D. W. Johnston, Eds.). Smith-
assistance in the early stages of the project, L. Gates, .sonian Inst. Press, Washington, D.C.
D. Brunetti, W. DeLuca and S. Clarke for assistance Marra, P. P, K. a. Hobson, and R. T. Holmes. 1998.
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Island National Wildlife Refuge for logistic support, of dominance-mediated habitat segregation in a
and we thank the staff of the Boqueron Bird Refuge migrant passerine bird during the non-breeding
for permission to establish our study plot. season. Auk 118:92-104.
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