Nest Density and Success of Columbids in Puerto Rico ’

Home , Bird conservation, Grenada dove, Parrot, Plain pigeon, Zenaida dove, Zenaida doves

The Condor98:1OC-113 0 The CooperOrnithological Society 1996

NEST DENSITY AND SUCCESS OF COLUMBIDS IN PUERTO RICO ’

FRANK F. RIVERA-MILAN~ Department ofNatural Resources,Scientific Research Area, TerrestrialEcology Section, Stop 3 Puerta. de Tierra, 00906, Puerto Rico

Abstract. A total of 868 active nests of eight speciesof pigeonsand doves (columbids) were found in 210 0.1 ha strip-transectssampled in the three major life zones of Puerto Rico from February 1987 to June 1992. The columbids had a peak in nest density in May and June, with a decline during the July to October flocking period, and an increasefrom November to April. Predation accountedfor 8 1% of the nest lossesobserved from 1989 to 1992. Nest cover was the most important microhabitat variable accountingfor nest failure or successaccording to univariate and multivariate comparisons. The daily survival rate estimates of nests constructed on epiphytes were significantly higher than those of nests constructedon the bare branchesof trees. Rainfall of the first six months of the year during the study accounted for 67% and 71% of the variability associatedwith the nest density estimatesof the columbids during the reproductivepeak in the xerophytic forest of Gulnica and dry coastal forest of Cabo Rojo, but only 9% of the variability of the nest density estimatesof the columbids in the moist montane second-growthforest patchesof Cidra. In 1988, the abundance of fruits of key tree species(nine speciescombined) was positively correlatedwith the seasonalchanges in nest density of the columbids in the strip-transects of Cayey and Cidra. Pairwise density correlationsamong the columbids suggestedparallel responsesof nestingpopulations to similar or covarying resourcesin the life zones of Puerto Rico. Key words: Columbidae; strip-transects;nest density; nestingsuccess; microhabitat: rainfall; fruit abundance;species covariations; seasons; life zones;Puerto Rico.

INTRODUCTION Collazo-Algarin 1976; Arendt et al. 1979; Wiley Ten native species of Columbidae (columbids 1979,1985, 1991; Wiley and Wiley 1979; Block- hereafter) occur in Puerto Rico: Zenaida Dove stein 1988; Bancroft et al. 1990; Godinez 1993). (Zenaida aurita), White-winged Dove (Z. asia- Habitat lossand illegal hunting have been ranked tica), Mourning Dove (Z. macroura), Common as the principal threats to species such as the Ground-Dove (Columbina passerina), Scaly- Plain Pigeon and White-crowned Pigeon in Puer- naped Pigeon (Columba squamosa), White- to Rico (Wiley 1985). Therefore, our manage- crowned Pigeon (C. leucocephala), Plain Pigeon ment decisions should be guided by reliable es- (C. inornata), Ruddy Quail Dove (Geotrygon timates of the size and successof nesting popu- montana), Key West Quail Dove (G. chrysia), lations at local scales(e.g., the 15 forest reserves and Bridled Quail Dove (G. mystaceu). General of the Puerto Rican mainland, which range in information about the columbids in Puerto Rico size from ca. 140 to 11,300 ha; Birdsey and can be found in Biaggi ( 1970) and Raffaele ( 1989). Weaver 1982, Silander et al. 1986). Additional information about their distribution In this study I examine: (1) the seasonalchanges and abundance can be found in Rivera-Milan in nest density and covariation patterns for eight (1990, 1992, 1993, 1995). of ten native speciesof pigeons and doves in the In Puerto Rico and on other Caribbean islands, three major life zones of Puerto Rico (1987- there is a need to monitor bird populations, and 1988); (2) the annual changesin nest density in to manage and protect nesting habitats that re- the moist montane second-growthforest patches main relatively undisturbed (Perez-Rivera and of Cidra, the State Forest of Guanica (xerophytic forest hereafter), and the dry coastal forest of Cabo Rojo (1987-1992); (3) the relationship between changesin nest density during the reproductive peak and rainfall of the first six months I Received 16 May 1995.Accepted 5 September1995. 2 Current address: U.S. Fish and Wildlife Service, of the year in Cabo Rojo, Cidra, and Gudnica Office of International Affairs, 4401 North Fairfax (1987-1992); (4) the associations between the Drive, Suite 860-ARLSQ, Arlington, VA 22203. seasonal changesin nest density and the abun-

[lOOI NESTING BY COLUMBIDS IN PUERTO RICO 101

dance of fruits of key tree speciesin Cayey and A total of 210 0.1 ha (100 x 10 m) strip- Cidra (1988); and (5) the nesting successesti- transects (158 in the dry zone, 36 in the moist mates of the columbids and the effects of six zone, and 16 in the wet zone) were sampled in microhabitat variables on nest failure or success 1988; 110 0.1 ha strip-transects(48 in Cabo Rojo, in Cabo Rojo, Cidra, and Guanica (1989-1992). 46 in Guanica, and 16 in Cidra) were sampled The aim of this study is to promote a better from 1987 to 1992. A nest was consideredactive understanding of the dynamics of columbid nest- when eggs,nestlings, or incubating adults were ing populations at multiple spatial (habitats, life present, When possible, incubating adults were zones) and temporal (seasons,years) scales on not flushedfrom their neststo avoid unnecessary the Puerto Rican mainland. The White-crowned disturbance. Flagging was attached to branches Pigeon and Bridled Quail Dove were not includ- or trunks at least 5 m from active nests. From ed in this study becausethey were not observed 1987 to 1992, I sampled all the strip-transects nesting in any of the study areas sampled on the with the assistanceoftwo trained personsto min- Puerto Rican mainland from 1987 to 1992. imize observer and habitat differences in nest detection probability (Nichols et al. 1986; Ri- STUDY AREAS AND METHODS Vera-Milan 1990; l&era-Milan et al. 1990, 1993; LIFE ZONES Rivera-Milan, unpubl. data). While searchingfor Puerto Rico is the smallest (8,903 km2) and east- active nests, I kept a record of all the avian and ernmost (55”17’-35”18’N, 37”65’-17”67’W) is- mammalian predators seeninside the area of the land of the Greater Antilles. Ewe1and Whitmore strip-transects. The density estimates of preda- (1973) classified the three major life zones of tors are presented for all speciescombined at a Puerto Rico as a subtropical moist zone (5,326 locality; the density estimatesof predator species km2), a subtropical wet zone (2,124 km2), and a per locality will be published elsewhere(Rivera- subtropical dry zone (1,216 km2; Fig. 1). Milan, unpubl. data). Nesting successwas estimated accordingto the NESTING HABITATS Mayfield method (Mayfield 196 1,1975; Johnson The habitats sampled in the dry zone were the 1979). The lengths of the incubation and nestling xerophytic forest of Guanica (ca. 4,006 ha; 4.6 periods were assumed to be 14 and 12 days for ha sampled from 1987 to 1992) the dry coastal all the species(Hanson and Kossack 1963, Wiley forest of Cabo Rojo (ca. 803 ha; 4.8 ha sampled 1991). A nest was classified as successfulif at from 1987 to 1992), and the mango (Mungiferu least one nestling reachedday 12. Nests that were indicu) farms and surrounding dry coastal forest not found after the first visit, or that were found patchesof Juana Diaz and Santa Isabel (ca. 292 completely or partially destroyed and contained ha; 6.4 ha sampled in 1988). The habitats sam- little or no feces,were classifiedas unsuccessful. pled in the moist zone were the montane second- Nest losseswere recordedas causedby predators growth forest patches of Cidra (ca. 5 10 ha; 1.6 (avian or mammalian), human-induced (e.g., ha sampled from 1987 to 1992, and 3.6 ha sam- damage to nest trees), or natural (e.g., inclement pled in 1988); and in the wet zone, the montane weather). Active nests were visited a maximum second-growth forest patches bordering Carite of three times (at intervals of approximately 10 Lake that are adjacent to the Carite State Forest, days) to minimize observer-induced disturbance Cayey (ca. 2,695 ha; 1.6 ha sampled from 1987 (Nichols et al. 1984, Westmoreland and Best to 1991; Fig. 1). Refer to the Appendix for in- 1985, Gotmark 1992, and referencestherein). formation about the vegetation of the mesic and MICROHABITAT VARIABLES xeric habitats sampled from 1987 to 1992. Six microhabitat variables were measured im- NEST DENSITY AND SUCCESS ESTIMATES mediately after determining the fate of a nest: Nest counts were conducted on a year-round ba- height of nest tree (m), height of nest above the sisfromFebruary1987toDecember1988.From ground (m), diameter at breast height (DBH) of 1989 to 1992, nest counts were conducted from nest tree (cm), perpendicular distance from be- the second week of May to the second week of low the nest to the center of the strip-transect June to cover the reproductive peak of the col- (m), mean relative cover at 5 m from the nest umbids on the Puerto Rican mainland (Rivera- (see below), and distance from the center of the Milan 1990). nest-bowl to the trunk of the nest tree (cm). 102 FRANK F. RIVERA-MILh4

Relative cover was calculated as the mean of Becauseof the number of strip-transectssam- four visibility measurements made at 5 m from pled in the dry zone in 1988 (n = 158), I did not a previously active nest in the four cardinal di- conduct detailed observations of the abundance rections using a compass, a tape measure, and of fruits of tree speciesin that zone. However, an ocular tube (James and Shugart 1970). Each casual observations made inside and outside the relative cover measurement was recorded as 0 = areassampled suggestthat the fruits of trees such poor, 1 = fair, 2 = good, or 3 = excellent. Nests as pigeon berry (Boureriasucculenta), turpentine were also classified as constructed on the bare tree (Burserasimaruba), and Crotonrigidus, and branches of trees (0) or on epiphytes (1; bro- the seedsof grassessuch as Argemonemexicana, meliads, lianas, and vines). From 1989 to 1992, Panicummaximum, and Amaranthusdubius are I conducted all the microhabitat measurements important food sourcesfor the columbids in the with the assistanceof two trained personsto avoid dry zone during the nesting season(also seeMal- inter-observer effects(Block et al. 1987, Rivera- donado-Colon and Perez-Rivera 1977, PCrez- Milan et al. 1993). Rivera 1987, Wiley 199 1, and referencestherein).

RAINFALL The rainfall data were obtained from pluviom- STATISTICAL ANALYSES eters in the Guanica State Forest (Puerto Rico The nest data were analyzed for each speciessep- Department of Natural Resources,unpubl. data) arately and for all speciescombined at a locality. and the Cabo Rojo National Wildlife Refuge(U.S. When necessary, the nest data were log-trans- Fish and Wildlife Service, unpubl. data) from formed to meet the assumptions of parametric 1984 to 1992. The climatological summaries tests (Sokal and Rohlf 198 1). published by the National Oceanic and Atmo- Analysis of variance (ANOVA) with repeated spheric Administration (NOAA) were used to measures at one factor (time) was used to ex- obtain the rainfall data of Cidra from 1984 to amine the seasonal and annual changesin nest 1992. density of the columbids in the strip-transectsof the life zones (Winer 197 1; Gurevitch and Ches- ter 1986; Beal and Khamis 1990, 1991; Quinn FRUIT ABUNDANCE and Keough 199 1). Polynomial contrasts(linear, In 1988, I conductedbinocular observationsfrom quadratic, and cubic) were used to examine the the ground in 15 of the 52 strip-transectsestab- relationshipsof time (seasonsand years)and nest- lished at Cayey (n = 8) and Cidra (n = 7) to counts (Winer 197 1). Greenhouse-Geisser ad- determine the abundance of mature and im- justment was used to correct the P-values of uni- mature fruits (combined) of Puerto Rican royal- variate ANOVAs with repeated measures(Gur- palm (Roystoneaborinquena), Martinique prick- evitch and Chester 1986; Beal and Khamis 1990, ly-ash (Zanthoxylummartinicense), trumpet tree 199 1; Quinn and Keough 199 1). (Cecropiashreberiana), matchwood (Dydimo- Simple linear regressionwas used to examine panax morototoni),punch berry (Myrcia splen- the relationships between changesin nest density dens),camasey (Miconiaprasina), India laurel- and rainfall of the first six months of the year in fig (Ficuscitrifolia), apple rose (Syzygiumjam- Cabo Rojo, Cidra, and Gubnica. Pearson’s Prod- bos),and night shade (Solanumtorvum). These uct-Moment Coefficient of Correlation (r) was tree speciesare consideredimportant food sources used to examine the relationships between of pigeons and doves in the montane second- changes in nest density and the abundance of growth forestsof the moist and wet zones (PCrez- fruits of key tree speciesin the strip-transectsof Rivera and Collazo-Algarin 1976, Maldonado- Cayey and Cidra. Pearson’s r was also used to Colon and Perez-Rivera 1977, Perez-Rivera measure the relative intensity of seasonal nest 1979, Cardona et al. 1986, Wiley 199 1, Rivera- density covariations of the columbids in the life Milan, unpubl. data). While searchingfor active zones (Sokal and Rohlf 198 1, Ludwig and Reyn- nests, I ranked fruit abundance per tree as 1 = olds 1988). low, 2 = moderate, or 3 = high, and calculated ANOVA and multivariate analysis of variance a mean per species per month (Rivera-Milan (MANOVA) were used to carry out univariate 1990, 1992). and multivariate comparisons of the six micro- NESTING BY COLUMBIDS IN PUERTO RICO 103

6715’ o 20 40km 6545’ 0 I f

5: Guhica 6: Cabo Rojo

FIGURE 1. Map of Puerto Rico showing the study areas sampled in the three major life zones of the Puerto Rican mainland.

habitat variables measured at nest trees (Dillon RESULTS and Goldstein 1984, Block et al. 1987). Estimates of daily survival rate (DSR) were used to carry SEASONAL CHANGES IN NEST DENSITY out a one-tailed Z-test of the equality of nesting IN THE LIFE ZONES successof the columbids in Cabo Rojo, Cidra, In 1988, a total of 341 active nests were found and Guanica (i.e., intra- and interspecific com- in the 158 0.1 ha strip-transectsof the dry zone, parisons within and between the localities; Steel whereas 193 active nests were found in the 52 and Torrie 1980). A one-tailed Z-test was also 0.1 ha strip-transectsof the wet and moist zones. used to compare the DSRs of nests constructed The columbids (eight speciescombined) had a on epiphytes and on the bare branches of trees peak in nest density in May and June, with a (Steel and Torrie 1980). decline from July to October (the flocking peri- Statistical analyses were performed with the od), and an increase from November to April programs SuperANOVA and StatView II (Ab- (Table 1, Figs. 2 and 3A, B). The significant sec- acus Concepts, Inc., Berkeley, CA). Significance ond degreepolynomial contrast suggesteda cur- was acceptedat P f: 0.05. vilinear relationship between time and nest-

TABLE 1. Analysis of variance (ANOVA) with repeated measuresat one factor (seasons)for nest counts of the columbids (combined) in the three major life zones of Puerto Rico. Sampling period: January-December 1988”.

sourceVariation df ss MS F P

Life zone 1 0.011 0.011 0.007 0.9347 Species(Life zone) I 10.413 1.488 Season 15.904 5.301 22.928 0.000 1 Season x life zone : 0.602 0.201 0.868 0.4437 Season x species (Life zone) 21 4.856 0.23 1 Repeated Measures: Winter Spring Summer Autumn Life zone: Moist-wet 0.976 2.164 2.388 0.500 Dry 1.208 1.871 2.247 0.841 Means table: Effect: season 1.105 2.002 2.310 0.689 Linear contrast F = 1.789, P = 0.1931 Quadratic contrast F = 63.639, P = 0.0001 Cubic contrast F = 3.356, P = 0.0961

* The ANOVA model used was: yij. = P + m, + mu,, + 0, + ~4, + B?rias+ ~q (Winer 1971:5 18-539). Nest COUII~Swere lo~transformed. 104 FRANK F. RIVERA-MILAN

in 1989 and 1991, followed by an increase in 1992 (Table 2, Fig. 4B). A total of 82 active nests were found in the strip-transects of the dry coastal forest of Cabo Rojo from 1987 to 1992. There was a decrease in the mean nest density estimates of the columbids in 1990 and 199 1, followed by an increasein 1992 (Table 2, Fig. 4C).

ANNUAL CHANGES IN NEST DENSITY AND RAINFALL The rainfall of the first six months of the year explained 67% and 7 1% of the variability asso-

0 FMAMJJASONDJFMAMJJ Months (1987-88) FIGURE 2. Nest density estimates of Common Ground-Doves(CGD), Scaly-napedPigeons (SNP), and Zenaida Doves (ZD) in 126 0.1 -ha strip-transectssampled in Cabo Rojo, Cayey, Cidra, and Guanica, Puerto Rico, from February 1987to July 1988. Ground Doves, White-winged Doves, and Mourning Doves were not observednesting in any of the strip-transectssampled in the moist and wet zones from 1987 to 1988. Scaly- naped Pigeons,Plain Pigeons,and Ruddy Quail Doves were not observednesting in any of the strip-transects sampled in the dry zone from 1987 to 1988.

counts (i.e., a seasonal increase followed by a -I Jan Feb Mar Apr May Jun Jul Aug Sep 001 NW Ccc decreasein nest density in the life zones; Table 5 1). The seasonal nesting pattern remained un- changed from 1987 to 1988, with June having the highestnest density in both years (Figs. 2 and 3A, B). Although active nests of speciessuch as Common Ground-Doves, Zenaida Doves, and Scaly-naped Pigeonswere found on a year-round basis in the strip-transects of the life zones, the nesting activity occurring from Septemberto No- vember was minimal (Table 1, Figs. 2 and 3A, B). ANNUAL CHANGES IN NEST DENSITY IN CIDRA, GUANICA, AND CAB0 ROJO A total of 105 active nests were found in the 0 Jan Feb Mar Apr May Jun Jul Aug Sep Ott NW Dee strip-transects of the moist montane second- Months (1988) growth forestpatches of Cidra from 1987 to 1992. FIGURE 3. (A) Nest density estimates of Key West There was a decreasein the mean nest density Quail Doves (KWQD), Ground Doves (CGD), Zena- estimates of the columbids in 1989 and 1990, ida Doves (ZD), Mourning Doves (MD), and White- followed by an increasein 199 1 and 1992 (Table winged Doves (WWD) in 158 0.1 ha strip-transects 2, Fig. 4A). sampledin the dry zone of Puerto Rico from January- A total of 46 active nests were found in the December 1988. (B) Nest density estimates of Plain Pigeons(PP), Ruddy and Key West Quail Doves (QDs), strip-transectsof the xerophytic forestsof Guan- Scaly-napedPigeons (SNP), and Zenaida Doves (ZD) ica from 1987 to 1992. There was a decreasein in 52 0.1 ha strip-transectssampled in the moist and the mean nest density estimatesof the columbids wet zones from Januaryto December1988. NESTING BY COLUMBIDS IN PUERTO RICO 105

A: Cidra ciated with the nest density estimates of all columbids combined during the reproductive peak of May and June in the strip-transects of the xerophytic forest of Gulnica (1987-1992: p, = 0.048, 95% confidence intervals (CI) = 0.002- 0.095, P = 0.05; Fig. 4B) and the dry coastal forestofCaboRojo(1987-1992:& = 0.107,95% CI = 0.012-0.203, P = 0.04; Fig. 4C). It only explained 9% of the variability of the nest density estimatesin the strip-transectsof the moist montane second-growthforest patches of Cidra (1987- 1992: P, = 0.101,95% CI = -0.339-0.541, P = " 19.37 19ee 19as 1990 19.91 1992 0.69; Fig. 4A). (65.65) (67.94)(72.03)(66.43)(45.04) (79.56) SEASONALCHANGES IN NEST DENSITY AND FRUIT ABUNDANCE In 1988, the seasonalchanges in nest density of the columbids (Scaly-naped Pigeons, Zenaida Doves, Plain Pigeons, Ruddy Quail Doves, and Key West Quail Doves combined) were positively correlated with the abundance of mature and immature fruits of key tree species(nine species combined) in the strip-transects of Cayey and Cidra (r = 0.54, P = 0.071, IZ = 12). The apple rose (r = 0.71, P = 0.009), night shade (r = 0.59, P = 0.045), and trumpet tree (r = 0.55, - 19a7 19ea 1989 1990 19'91 1992 P = 0.064) had the highest correlations with the (46.74)(23.67)(22.40)(36.61)(23.14)(51.79) , nest density estimates of the columbids (also see Rivera-Milan 1990, 1992).

NESTING SUCCESSESTIMATES AND MICROHABITAT VARIABLES Of 224 active nests, 144 (64%) were unsuccessful. Predation accounted for 8 1% ( 116 of 144) of the nest lossesobserved from 1989 to 1992 (Table 3). The density of avian and mammalian predators combined was higher in the strip-transects of Cabo Rojo than in thoseof Cidra and Guanica; but it was higher in the strip-transects of Cidra than in those of Guanica (Table 3). Human-in- 1967 1966 1969 1990 IS& 1992 duced disturbance such as damage to nest trees (47.24)(14.46)(36.66) (35.05) (27.03)(63.46) accounted for 12%, and inclement weather for Years 7% of the nest lossesobserved from 1989 to 1992. Rainfall (cm) The Zenaida Doves had a nesting successof FIGURE 4. Annual changesin themean nest density estimatesof the columbidsin the moist montanesec- 49% in Guanica, 47% in Cidra, and 22% in Cabo ond-growthforest patches of Cidra (A, n = 16 strip- Rojo. The Scaly-naped Pigeons had a nesting transects),the xerophytic forest of Guinica (B; n = 46), successof 44% in Cidra. In Cabo Rojo, the White- and the dry coastalforest of Cabo Rojo (C, n = 48) winged Doves had a nesting successof 29%, and from May-June 1987to 1992.The rainfall of the first six monthsof the year is given within parenthesesin the Mourning Doves of 2 l%, and the Ground the x-axis.Abbreviations are as in Figs.2 and 3A, B. Doves of 17% (Table 3). The nests of Zenaida Doves in Guanica and Cidra had higher estimates of daily survival rate (DSR) than those of the other columbids in Cidra and Cabo Rojo. In 106 FRANK F. RIVERA-MILAN

TABLE 2. One-way analysisof variance (ANOVA) with repeatedmeasures at one factor (years)for nest counts of the columbids (combined) in the moist montane second-growth forest of Cidra, the xerophytic forest of Guanica, and the dry coastalforest of Cabo Rojo. Sampling period: May-June 1987-1992’.

sourcevariation df SS MS F P

Locality 63.955 31.977 2.174 0.1762 Species(locality) 117.676 14.709 Year 5 17.519 3.504 3.928 0.0339 Year x locality 10 13.532 1.353 1.517 0.2359 Year x species(locality) 40 36.676 0.892 Repeated Measures: 1987 1988 1989 1990 1991 1992 Locality: Cidra 3.283 3.595 1.717 0.940 2.660 3.910 Guanica 0.797 0.650 0.217 0.507 0.290 0.867 Cabo Rojo 0.733 0.470 0.730 0.380 0.210 1.720 Means Table: Effect: Year 1.677 1.655 0.949 0.618 1.123 2.284 Linear contrast F = 0.164, P = 0.4889 Quadratic contrast F = 15.099, P = 0.0057 Cubic contrast F = 3.833, P = 0.0834

. The ANOVA model usedwas: Ytik = p + a, + rKx)+ S, + &3,,+ ,9r,, + etiukj(Winer 19715 18-539). Nest countswere log-tranfonned.

contrast, the nestsof the columbids in Cabo Rojo 146) in Cabo Rojo, Cidra, and Guanica (com- had lower DSRs than thosein Guinica and Cidra bined; Z-value = 5.487, P < 0.001). (Table 3). The estimated DSR of nestsconstruct- According to univariate and multivariate ed on epiphytes(DSR = 0.97 1,95% CI = 0.959 l- comparisons, the mean relative cover at 5 m 0.9829, n = 78) was significantly higher than that from active nests was the most important mi- of nestsconstructed on the bare branchesof trees crohabitat variable accounting for the reproduc- (DSR = 0.944, 95% CI = 0.9217-0.9556, n = tive failure or successof the columbids in Cidra,

TABLE 3. Nesting successestimates of the columbids in the moist montane second-growthforest of Cidra, the xerophytic forest of Guanica, and the dry coastal forest of Cabo Rojo. Sampling period: May-June 1989- 1992’.

Number SUCCeSS Predation/ Predatormean SpeCi& of nests DSR (SE& estimate(%)” nestlossw density(SE) ’

Cidra: moist montane second-growthforests SNP 40 0.968 (0.0072)‘) 44 16/18 (89%) 5.94 (1.133) ZD 31 0.971 (0.0062)8 47 17/21 (81%) Guanica: xerophytic foresth ZD 42 0.973 (0.0076)8 49 24/30 (80%) 2.65 (0.592) Cabo Rojo: dry coastal forest CGD 51 0.935 (0.0105)~ 17 33/36 (92%) 9.39 (1.668) MD 0.941 (0.0132)D 21 13/19 (68%) WWD z 0.953 (0.0133)C 29 8/l 2 (67%) ZD 13 0.943 (0.0195)D 22 5/8 (63%) a A nestingperiod of 26 dayswas assumed for all the species. bAbbreviations: Scaly-naped Pigeon (SNP); ikaida Dove (ZD); CommonGround-Dove (CGD); Mourning Dove (MD); and White-wingedDove ,wwnr\.. ..-,. * Daily survival rates(+ standarderror) followed by differentsuperscripts differed significantly at P d 0.05 (one-tailed Z-tests). Daily survival ratesfollowed by similar superscriptsdid not differ significantlyat P 5 0.05. d Mayfields’ method. e Number of nestspredated divided b the total numberof nestlosses recorded due to predation(avian or mammalian)or any othernatural (e.g., inclementweather) or human-inducedI e.g.,damage to nesttrees) cause. ‘Mean numberof avian and mammalian predators(combined) per ha (k standarderror). 6 It was not possibleto estimatenesting sucxxss for all the nestsfound active in the moist montanesecond-growth forest patches because of nest heightand inaccessibility(see Table 4). h Someactive nestsfound outsideof the strip-transectsof the xerophyticand dry coastalforests were included in the estimatesof nestingsuccess of White-wingedDoves, Mourning Doves, and Zenaida Doves to increasethe sample-sizesper habitat type. NESTING BY COLUMBIDS IN PUERTO RICO 107

TABLE 4. Univariate comparisonsof nest tree microhabitat variables of successfuland unsuccessfulnests of the columbids (combined) in the moist montane second-growthforest of Cidra, the xerophytic forest of Gulnica, and the dry coastal forest of Cabo Rojo. Sampling period: May-June 1989-1992.’

Variabl& x SE; n F P

Cidra: moist montane second-growthforest 1. Nest tree height (m) Unsuccessful 12.81 2.024 14 0.095 0.761 Successful 13.87 2.897 10 2. Nest height (m) Unsuccessful 7.61 0.888 14 3.306 0.083 Successful 5.54 0.506 10 3. Nest tree DBH (cm) Unsuccessful 21.98 3.393 14 1.107 0.304 Successful 29.3 1 6.600 11 4. Perpendiculardistance from nest to transect center (m) Unsuccessful 10.84 1.967 14 0.655 0.427 Successful 12.83 1.155 11 5. Mean relative cover of nest at 5 m Unsuccessful 1.68 0.217 14 23.982 0.0001 Successful 2.90 0.049 11 6. Distance from nest-bowl center to tree trunk (cm) Unsuccessful 240.07 47.252 14 2.562 0.124 Successful 128.10 49.618 10 Cabo Rojo and Gulnica: xerophytic and dry coastal forest 1. Nest tree height (m) Unsuccessful 3.87 0.286 28 2.367 0.131 Successful 4.69 0.503 17 2. Nest height (m) Unsuccessful 2.19 0.176 28 0.567 0.455 Successful 2.43 0.282 17 3. Nest tree DBH (cm) Unsuccessful 12.77 1.521 28 0.350 0.557 Successful 14.16 1.684 17 4. Perpendiculardistance from nest to transect center (m) Unsuccessful 6.64 1.253 28 4.329 0.043 Successful 11.83 1.957 17 5. Mean relative cover of nest at 5 m Unsuccessful 2.09 0.104 28 11.182 0.002 Successful 2.60 0.093 17 6. Distance from nest-bowl center to tree trunk (cm) Unsuccessful 24.44 47.252 28 0.267 0.871 Successful 26.18 10.276 17

* One-wayANOVAs. The nestsofZenai& Doves,Scaly-naped Pigeons, and PlainPigeons were combined in Cidra. The nestsof CommonGround- Doves,White-winged Doves, Mourning Doves, and ZenaidaDoves were combinedin Cabo Rojo and G&ka. b SeeMethods.

Cabo Rojo and Guanica (MANOVAs: Cidm F,,,6 (MANOVA: F,,+ = 1.172,P=0.2951;seeTable = 5.981, P = 0.0264; Cabo Rojo and Gudnica: 4 for ANOVAs and descriptive statisticsof mi- F,,3,= 7.983, P = 0.0076; overall: F,,6,= 20.877, crohabitat variables). A list of the number of P = 0.0001; Table 4). The second most impor- active nests found per tree speciesper locality is tant microhabitat variable measured in the xer- given in the Appendix. ophytic and dry coastal forests was the perpendicular distance from the nests to the center of SEASONAL SPECIES COVARIATIONS IN NEST the strip-transects (MANOVA: F,,37= 1.626, P DENSITY IN THE LIW ZONES = 0.2102). Nest height was the second most im- Pearson’s (r) correlation coefficients showed sim- portant microhabitat variable measured in the ilar patterns of speciescovariations in the strip- moist montane second-growth forest patches transects of the life zones (Table 5). The nest 108 FRANK F. RIVERA-MILAN density estimates of Scaly-naped Pigeons, Plain TABLE 5. Pearson’sProduct-Moment Coefficientsof Pigeons, Zenaida Doves, and Ruddy and Key Correlation (r; upper-right triangle) and covariances (lower-left triangle) of nest-countsof the columbids in West Quail Doves (combined) were positively the three major life zones of Puerto Rico. Sampling correlated in the strip-transectsof the moist and period: January-December 1988.’ wet zones, whereasthe nest density estimates of Ground Doves, Zenaida Doves, Mourning Life zone Species Doves, White-winged Doves, and Key West Quail Dry Zone (area sampled: 15.8 ha) Doves were positively correlated in the strip- ZDb CGD MD WWD KWQD transectsof the dry zone (Table 5). The predom- 0.65* 0.83* 0.80* 0.38ns inantly positive and significant correlations (13 ;:D o_lo 0.71* 0.64* 0.53ns of 16) suggestedparallel responsesof columbid MD 0.12 o.lo 0.76* 0.50” nesting populations to similar or covarying re- WWD 0.10 0.06 0.08 0.74* sourcesin the life zones of Puerto Rico (Rivera- KWQD 0.04 0.04 0.04 0.05 - Mildn 1990, 1992, 1995). Moist and Wet Zones (area sampled: 5.2 ha) SNP ZD PP QDs SNP 0.83* 0.88* 0.91* DISCUSSION ZD 0.22 0.94* 0.90* 0.20 0.21 0.93* SEASONAL AND ANNUAL CHANGES IN NEST & 0.13 0.13 o-12 - DENSITY ‘A total of 210 0.1 ha strip-transectswere sampled in 1988 (158 in A peak in the nest density of the columbids oc- the dry zone,36 in the moist zone,and 16 in the wet zone).Nest counts wereIon-transformed. curred in May and June, followed by a decrease b Abbkiations as in Table 1. * Signi&+ at P 5 0.05. during the July to October flocking period (see -Not stgnlficantat P 5 0.05. Rivera-Milti 1990, 1992, 1993, 1995), and an increase from November to April (Figs. 2 and the columbid nesting populations rebounded to 3A, B, Table 1). A second degree (quadratic) pre-Hurricane levels from 199 1 to 1992 (Fig. polynomial model showedan adequate fit to the 4A). observed seasonalchanges in nest density of the Cabo Rojo and Guinica were not affected by columbids in the life zones from 1987 to 1988 Hurricane Hugo. The mean nest density esti- (Table 2). Although a peak in nest density oc- mates of the columbids (Zenaida Doves, Com- curred in May and June, active nests of species mon Ground-Doves, and Key West Quail Doves such as Ground Doves, Zenaida Doves, and combined) decreased in Gutiica in 1989 and Scaly-naped Pigeons were observed throughout 199 1 (Fig. 4B), whereas the mean nest density the year in the study areas sampled from 1987 estimates of the columbids (Ground Doves, Ze- to 1988 (see below). naida Doves, White-winged Doves, and Moum- A quadratic polynomial model showedan ad- ing Doves combined) decreasedin Cabo Rojo in equate fit to the changesobserved in Cabo Rojo, 1990 and 199 1 (Fig. 4C). The mean nest density Cidra, and Gu&nica from 1987 to 1992 (Fig. 4A- estimates in Cabo Rojo and Gutiica increased C, Table 2). The mean nest density estimates of in 1992. The rainfall of the first six months of the columbids (Scaly-naped Pigeons, Zenaida the year influenced the changes observed from Doves, Plain Pigeons, Ruddy Quail Doves, and 1987 to 1992 (see below). Key West Quail Doves combined) decreasedin Cidra in 1990, probably due to the effect of the NESTING SUCCESS, MICROHABITAT passageof Hurricane Hugo through the north- VARIABLES, AND PREDATION eastern comer of Puerto Rico on 18 September The estimatesof nesting successof the columbids 1989 (see Brennan 199 1, Boose et al. 1994, and in Guanica and Cidra were significantly higher referencestherein). Some fmgivore and seed-eat- than those in Cabo Rojo (Table 3). Nest cover ing bird populations were severely affectedboth was the most important microhabitat variable short-term direct effects and long-term indirect accounting for failure or success(Table 4). Pre- effectsby this large-scaleenvironmental pertur- dation on eggsor nestlings was the major cause bation (e.g., Ruddy Quail Doves; seeWaide 199 1, of failure. Nests constructed on epiphytes (bro- Wauer and Wunderle 1992, Wiley and Wunderle meliads, lianas, and vines) had higher DSRs than 1993, Rivera-Milti, unpubl. data), but in Cidra those constructed on the bare branches of trees, NESTING BY COLUMBIDS IN PUERTO RICO 109

probably becauseepiphytes provided additional the areassampled, and estimated that an average support and concealment against predators(Nice of 40.9% (n = 22) of the nests with eggswere 1922, 1923; Coon et al. 1981; Best and Stauffer successful(i.e., at least one nestling fledged) in 1980; Yahner 1982; Martin and Roper 1988). southwestern Puerto Rico (Gubnica and Susua Epiphytes were uncommon in the dry coastal forestscombined) from 1974 to 1975, and 62.6% forest of Cabo Rojo, but were used as nest sub- (n = 91) were successfulin Cidra from 1974 to strates in areas dominated by oxhorn bucida 1982. Maldonado-Colon and Perez-Rivera (1977) (Bucida buseras).The use of epiphytes was also estimated a mean nesting successof 63% (n = reported by Barbour (1923) and Maldonado-Co- 78) for the Zenaida Doves in Cayey, Cidra, and ion and Perez-Rivera (1977; see below). Gulnica (combined) and reported that 54% (n = Predator density was higher in Cabo Rojo than 37) of the nests found in Cayey were constructed in Cidra and Guanica (Table 3). Common on bromeliads (Tillandsia sp. and Guzmania sp.). Ground-Doves had lower nesting successand However, Maldonado-Colon and Perez-Rivera higher predation rates than the other columbids (1977) and Wiley (199 1) apparently used the tra- in Cabo Rojo, probably becausethey had a high- ditional method to estimatenesting success; hence er density of active nestsand used a wide variety their estimates are probably biased high (see of microhabitats frequently with poor-fair cover Mayfield 1961, 1975; Johnson 1979). The Ze- (e.g., dry tree stumps near the ground). From naida Dove is a multibrooded habitat generalist 1987 to 1992, Common Ground-Doves (n = 2) that may change its nesting and foraging pref- Zenaida Doves (n = l), and Mourning Doves (n erencesthroughout the year in an opportunistic = 2) were observed nesting on top of old Ban- manner; but, as with the other columbids, it needs anaquit (Coereba jlaveola) and Puerto Rican to find sites with adequate horizontal support Bullfinch (Loxigilla portoricensis)nests in Cabo and concealment against predators to increase Rojo. Scaly-naped Pigeons were observed nest- the probability of nesting successfully(see Mar- ing on top of old rat (Rat&s spp.; n = 2) and tin 1992 for a review). Green Heron (Butorides virescens;n = 1) nests in Cidra and Cayey (Rivera-Milan, unpubl. data). SEASONAL PATTERNS OF SPECIES The other pigeons and doves were not observed COVARIATIONS using the old nests of other speciesas substrates, The density of active nests found between the but this appearsto be a widespreadnesting strat- secondweek of May and the secondweek of June egy among the columbids (Nice 1922, 1923; Mc- in the xerophytic forestof Guanica and dry coast- Clure 1943; Hanson and Kossack 1963; Coon et al forest of Cabo Rojo was significantly influ- al. 198 1; Goodwin 1983; Westmoreland et al. enced by the rainfall of the first six months of 1986; Sayre and Silvy 1993). the year (also see Faaborg 1982, Faaborg et al. While sitting quietly and motionless on eggs 1984). On average, the rainfall in the xerophytic or nestlings, the columbids appeared to rely on and dry coastal forestspeaked in May and from the concealment provided by their plumage col- October to November (Rivera-Milan 1990, oration and on vegetation cover to reduce the 1992). The first and smaller peak of rain in May risk of detection by predators(Swank 195 5, Mur- marked the end of the December to March dry ton 1965, Bestandstauffer 1980, Tomialojc 1980, season and normally was followed by a period Yahner 1982, Westmoreland and Best 1987, of increasing soil moisture and primary produc- Burger et al. 1989, Martin 1992). Nesting Com- tivity. The secondand greaterpeak of rain during mon Ground-Doves, Zenaida Doves, and October and November was normally followed Mourning Doves often performed distraction by a period of extended drynesscharacterized by displays when approached by an observer, but a deficit of soil moisture and a decline in vege- sometimes they could be approachedvery close- tation cover and primary productivity (Lug0 et ly before flushing from the nest, especially when al. 1978). The dry seasonprobably prevents the brooding recently hatchednestlings (Swank 195 5, occurrenceof a secondpeak in nest density from Burger et al. 1989, Sayre and Silvy 1993, Wiley September to November by exerting a strong se- 199 1, Rivera-Milan unpubl. data). lective force against reproductive successin the Wiley (199 1) concludedthat the Zenaida Doves xerophytic forest of Guanica and dry coastal for- used nest trees in relation to their abundance in est of Cabo Rojo. The decline in vegetation cover 110 FRANK F. RIVERA-MILm during the dry seasoncan increase the exposure columbids in the dry zone from 1987 to 1988 of active nests to predators such as Pearly-eyed (Rivera-Milan 1990, 1995). Thrashers (Murgurops &c&us), Red-legged The total amount of rainfall occurring during Thrushes (Turdus plumbeus), Mangrove Cuck- the first six months of the year was probably less 00s (Coccyzus minor), Puerto Rican Lizard- important than the abundance of fruits of key Cuckoos (Saurothera vieilloti), and rats among tree species (e.g., Syzygium jambos, Solanum others (Rivera-Milan 1990, 1992; Rivera-Milan torvum, and Cecropiashreberiana) as a predictor et al. 1993; Rivera-Milan and Schaffner,unpubl. of the seasonaland annual changesin nest den- data). sity of the columbids in the moist and wet zones Since columbids are capable of multiple (Cardona et al. 1986; Rivera-Milan 1990, 1992, brooding and crop-milk production, and they unpubl. data). Quantitative studies about the re- have a diverse frugivorous and granivorous diet, lationships between seasonaland annual changes complete synchronization of nesting events with in nest density and fruiting phenology of key tree foraging resources is not necessary to enhance speciesare needed to improve our understanding their reproductive success(Westmoreland and of the dynamics of columbid nesting populations Best 1987, Blockstein 1989, Wiley 1991; but see in mesic and xeric habitats (see, for example, Bancroft et al. 1990). For example, active nests Cardona et al. 1986, Bancroft et al. 1990). Nev- of Zenaida Doves and Ground Doves were found ertheless, the predominantly positive species at any time during the year in the strip-transects covariations suggestedparallel responsesof the of the dry zone. Both speciesmolted throughout columbid nesting populations to similar or co- the year (Rivera-Milan, unpubl. data). Male call- varying resourcesin the life zones of the Puerto ing activity was stimulated by rainfall in a bi- Rican mainland (Table 5). Quantification of modal fashion (Rivera-Milan 1990, 1992); and nesting and foragingresource use and availability probably they were ready to mate and breed is particularly important for the conservation and whenever the environmental conditions became management of columbid populations inside the favorable enough (e.g., adequate food supply and forest reservesof Puerto Rico. vegetationcover; Miller 1962, Immelmann 197 1, Fogden 1972, Mm-ton and Westwood 1977, Av- ACKNOWLEDGMENTS cry 1980, Wiley 1991). Part of this study was performed in partial fulfillment In the dry zone, the nesting activity of Com- of the requirementsfor the degree of Ph.D. from the mon Ground-Doves was less constrained than University of Maryland at CollegePark (UMCP). I that of the other columbids by rainfall (Figs. 2 thank J. Faaborg,F. SchafIher,and J. Wiley for .re- viewing the manuscript.I also thank G. Bonilla, E. and 3A). Common Ground-Doves feed mainly Gonzalez,A. Matos,S. Medina, A. Ortiz, J. Pagln, D. on grassseeds (Perez-I&era 1987), whereasthe R amos,E. Ramos,and C. Vazquezfor sharingmany other columbids feed on both seeds and fruits hoursafield. J. Vivaldi (deceased)and J. Morenonro- (Perez-Rivera and Collazo-Algarin 1976, Mal- vided supportas coordinators0; Pittman-RobeAson donado-Colbn and Perez-Rivera 1977, PCrez- Funds grant-in-aidto ProjectW- 11, Section of Ter- restrialEcology, Scientific Research Area, PuertoRico Rivera 1979, Wiley and Wiley 1979, Wiley 1991, Departmentof Natural Resources(PRDNR). M. Ca- and references therein). The fruits of key tree nals(PRDNR) providedthe rainfall dataof the GuBn- speciesin xeric habitats can be in short supply ica StateForest. J. Collazo,S. Rice, and F. Schaffner during dry years (Faaborg 1982, Faaborg et al. (U.S. Fishand Wildlife Service,Caribbean Islands Na- tional Wildlife Refuge)provided the rainfall data of 1984). Moreover, the mean body mass of the the Cabo Rojo National Wildlife Refuge.G. Proctor Common Ground-Dove is about 35 g, whereas (PRDNR) helpedwith theidentification of plants,seeds, the mean bodv mass of the other columbids in and fruits wheneverit was reauested.From 1987 to I the dry zone is over 100 g (Rivera-Milan, unpubl. 1988, I also receivedsupport through a researchas- data). Hence, Common Ground-Doves can sistantshipfrom the GraduateProgram in Marine and EstuarineEnvironmental Sciences and theAgricultural probably derive their energy and water require- and Life SciencesDivision at UMCP. ments more easily than the other columbids from a single foraging resource (grass seeds) that is LITERATURE CITED available throughout the year, especially during the peaks of rain in the dry zone (see MacMillen ARENDT,W. J.,T.A.V. MORA,ANDJ.W. WILEY. 1979. White-crownedPigeon: status rangewide in the 1990). With a mean density of 210.9 birds/km2 Dominican Republic.Proc. Ann. Conf. S.E. As- (95% CI = 102.9-3 18.8), the Common Ground- soc.Fish Wildl. Aeencies33: 11 l-l 22. Dove ranked as the most abundant among the AVERY, M. L. 1980. -Diet and breeding seasonality NESTING BY COLUMBIDS IN PUERTO RICO 111

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Vol. 10. Los bosquesde Puerto Rico. Puerto Rico Lodity Nlllllber Dept. Nat. Res. Nest tree ’ of nests SOKAL,R. R., ANDF. J. ROHL.F. 1981. Biometry. 2nd ed. W. H. Freeman and Co., San Francisco. Cidra: moist montane second-growthfoerst (n = 272)” SAYRE,M. W., AND N. J. Snvv. 1993. Nesting and Apple rose (Syzygiumjumbos) production, p. 8 l-104. In T. S. Baskett, M. W. Bamboo (Bambusa vulgaris) NESTING BY COLUMBIDS IN PUERTO RICO 113

APPENDIX. Continued.

African tuliptree (Spathodeucumpanulata) 43 American muskwood (Guareu trichilioides) 41 White cedar (Tabebuia heterophyla) 22 Martinique prickly-ash (Zanthoxylum mar- tinicense) 14 Mountain immortelle (Erythrina poeppi- gilWu2) 14 Trumpet tree (Cecropiushreberiuna) White manjack (Cordia sulcutu) 38 Puerto Rican royal-palm (Roystoneaborin- quena) 2 Guanica: xerophytic forest (n = 7 1)” Dildo (Cephalocereusroyeniz) 21 Prickly pear (Opuntiu rubescens) 17 Oxhom bucida (Bucidu bucerus) 16 Mahogany (Swietenia mahagoni) 11 Box briar (Randiu acute&z) 3 Turpentine tree (Burserasimaruba) 2 Caribbean princewood (Exostema cari- baeum) 1 Cabo Rojo: dry coastal forest (n = 254)” Dildo 64 Prickly pear 51 Mesquite (Prosopisspp.) 43 Guamuchil (Pithecellobiumduke) 32 Oxhom budica 28 Turpentine tree 15 Red mangrove (Rhizophoru mangle) 10 Black mangrove (Avicenniugerminans) 7 Button mangrove (Conocarpuserectus) 4

l Scientificnames followed Little et al. (1977). I ke t a completerecord of the nest treesused by each speciesper locality 5:om 1989 to 1992. Refer to P&ez-Rivera and Collazo-Algarln 1976). Mal+tado4316n and P$rez-Rivera(1977), Wiley and Wdey (16 79), and Wde (199 I) for ~2, mformatmnabout the nesttrees used by the columbt.J s III Puerto bRuddy and Key West Quail Dove nestswere commonlyfound on leafclumpsin unidentifiedshrubs, ferns, and treestumps near the ground (also seeP&ez-Rivem 1979). The nestsof Zenaida Doves, scaly-naped Pigeons,and Plain Pigeonswere combined.Epiphytes (bromeliads, lianas,,and vines) werecommonly used as nestsubstrates. The vegetation in C&a was characterizedby Puerto Rican royal-palm, West Indies trema (Treemalamarckiana), trumpet tree, India laurel-fig (&US citri- folia), machette(Erythrina bertemana), mountain immatelle, guaba(Inga vera),Martinique prickly-ash,American mu&wood, wild mamee(Chain rosea),punch berry (Myrcia splendenr). camasty (Mtconiaprarina), apple rose,matchwood (Dydim0pana.x morototonr), white manjack, night shade, African tuliptree,bamboo, and white cedaramong others. cThe nestsof Zenaida Doves, Ground Doves, and Ke West Quail- Doves were combined.Bromehads (Tillandsia SD.and E uzmania sp.) werecommonly used as nestsubstrates. The ve@3ationin Gtiica was chamcterizedby oxhom bucida,turpentine tree, dildo, prickly pear,pi- geonberry (Boureria succulenta f. ’ canbbean_,‘ pnncewood (Exostema car- ibaeum),sea amyis (Amyis e em&z), llgnumvltae (Guaiacumo I- nale),mahogany, box briar, and fustic (Pictetiaaculeara) among CI ti? en. d The nestsof CommonGround-Doves, White-winged Doves, Moum- ing Doves,and ZenaidaDoves werecombined. Bromeliids wereuncom- man, but were usedas nest substratesin forestpatches dominated by

mangrove(Laguncularia rademosa), black-mangrove, button-mangrove, whom bucida,turpentine tree, dildo, prickly pear,pigeon bay, lignmn- vitae, box briar, and fwic amongothers.