Efectos del “niño”

"El Niño" Effects on the Abundance and Habitat Association Patterns of Four Grebes Species

in Chilean Wetlands

Author(s): Yerko A. Vilina and Hernan Cofre

Source: Waterbirds: The International Journal of Waterbird Biology, Vol. 23, No. 1 (2000), pp.

95-101

Published by: Waterbird Society

Stable URL: http://www.jstor.org/stable/4641114

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International Journal of Waterbird Biology.

"El Nifio" Effects on the Abundance and Habitat Association Patterns

of Four Grebes Species in Chilean Wetlands

YERKO _{A. VILINA1 AND HERNAN COFRE2}

'Escuela de Medicina Veterinaria, Universidad Santo Tomdis. Ejercito 146, Santiago, Chile Internet: [email protected]

2Departamento de Ecologia, Facultad de Ciencias Biol6gicas, Pontificia Universidad Cat61lica de Chile. Casilla 114-D, Santiago, Chile

Internet: [email protected]

Abstract.-From July 1993 until November 1998 the authors studied the distribution, abundance and habitat association patterns of four grebes species, White-tufted Grebe (Rollandia rolland); the Silver Grebe (Podiceps occipi- talis), the Great Grebe, (Podiceps major), and the Pied-billed Grebe (Podilymbus podiceps), in a wetland of the Medi- terranean zone of Chile. Possible relationships between these patterns and increased precipitation associated with El Niflo-Southern Oscillation (ENSO) were also studied. The study was carried out in four wetland habitats over the 47 months. The results showed a positive correlation between the spring average abundance of these species and total rainfall in the previous year. Grebe populations increased in the summer of the year of the ENSO event and peaked in the spring of the post-ENSO year. The patterns of habitat association did not change with the quantity of rainfall. In general, the four species were associated mostly with seasonal habitats, which are deep and hold abun- dant emergent vegetation. The Silver Grebe uses this kind of habitat to establish breeding colonies only during ENSO and post-ENSO years. Received 24 August 1999, accepted 10 November 1999.

Key words.-ENSO, El Nifio, grebes, habitat, Mediterranean wetland, Podicipedidae, Southern Oscillation, wet- land. White-tufted Grebe, Rollandia rolland, Silver Grebe, Podiceps occipitalis, Great Grebe, Podiceps major, Pied-billed Grebe, Podilymbus podiceps.

Waterbirds 23(1): 95-101, 2000

The El Nifio-Southern Oscillation (EN-

SO) is a global phenomenon that causes

multiple effects on the western coastline of

the Americas (Arntz 1986; Glynn 1988). The

effect of this phenomenon on biological sys-

tems has only recently come under study (Bar-

ber and Chavez 1983), especially in intertidal

and marine fauna (Camus 1990; Castilla and

Camus 1992), including seabirds (Boersma

1978, 1998; Duffy and Merlen 1986; Hays 1986;

Araya 1987; Guerra et al. 1988; Duffy 1990).

The effect of ENSO events on South

American terrestrial fauna has been poorly

documented (Jaksic 1998); however, there is

evidence of periodic increases in small-mam-

mal abundance associated with ENSO distur-

bances in semi-arid regions of western South

America (Meserve et al. 1995; Jaksic et al.

1997; Lima et al. 1999). Studies of the effect

of ENSO disturbances on populations and

communities of continental waterbirds have

been scarce. We studied the presence, sea-

sonal abundance, and habitat association of

the four grebe species, White-tufted Grebe

(Rollandia rolland); Silver Grebe (Podiceps oc-

cipitalis), Great Grebe, (Podiceps major), and

Pied-billed Grebe (Podilymbus podiceps), that

inhabit a Mediterranean wetland in central

Chile. Here, we analyze the relationship be-

tween ENSO events, the high rainfall in that

wetland during this disturbance, and chang-

es in species abundance.

STUDY AREA AND METHODS

The wetland at the mouth of the El Yali stream,

33047'S, 71023'W, is located 20 km SSE of Port San An-

tonio, in Chile's 5th Region. The wetland is located in the subhumid Mediterranean region, with hot, dry sum- mers and cold, rainy winters. The rainy period generally lasts from April to September (Di Castri and Hajek 1976). The average annual rainfall during the last ten years recorded by the San Antonio Meteorology Station (33034'S, 71027'W) was 421.5 mm (779.5 mm maximum and 281.0 mm minimum). The average annual temper- ature is 13.2'C (Di Castri and Hajek 1976).

In this study, we surveyed four sites: El Rey lagoon, Los Molles reservoir, El Yali stream, and the Coastal la- goon (Fig. 1). These sites were selected as most repre- sentative of the different habitats in the wetland. El Rey lagoon and Los Molles reservoir are large (106 and 83 ha respectively), seasonal, and hold large areas of emer- gent and submergent vegetation. El Yali stream, 42 ha, is a permanent habitat that holds only floating vegeta- tion. The Coastal lagoon (94 ha) is a permanent habitat

96 WATERBIRDS

71 143'

N

Transects ---4

10

9

330

::

:

47--

Transects c .. ... Scale _1:66.000

0 ₁ 2

, km

Figure 1. Map of the study area in the El Yali wetland in central Chile. Dashed lines represent the fixed transects. The four sites studied were: 1 = Coastal lagoon, 3 = El Yali stream, 4 = El Rey lagoon and 6 = Los Molles reservoir.

with a sand beach and only floating vegetation. All hab- itats are eutrophic and they are shallow (depth < 3 m).

FromJuly 1993 to October 1998, we conducted a sea- sonal (one month or more per season) and simulta- neous census of each of the four sites of this wetland (n = 47). The abundance of grebes in each site was deter- mined through a direct count. The counts took place along fixed transects (Fig. 1), using the methodology of Kauppinen et al. (1990), between 0830 and 1400 h. The observer was the same person for each habitat, using 8 x 40 and 16 x 40 binoculars. The relationship between year and seasonal precipitation and population abun- dance of birds was analyzed graphically for the years 1993 to 1998. We applied linear regressions between yearly cumulative precipitation and population abun-

dance of these species during winter and spring in the same year, and between cumulative precipitation and population abundance of these species in the following winter and spring. The ENSO effect on habitat associa- tion patterns was analyzed with a chi-square test (Sokal and Rolf 1995).

RESULTS

"EL NIlO" EFFECT ON FOUR GREBES SPECIES

per month). Later, the population declined

and reached its lowest value, less than ten in-

dividuals per month, between December

1996 and May 1997 (Table 1). In the winter

of 1997 another ENSO event occurred, and

total rainfall exceeded 850 mm. During the

spring of 1997, the grebes showed an in-

creased abundance, reaching a maximum in

the spring of 1998, a post-ENSO year (550-

600 birds per month) (Fig. 2). To analyze

this time lag, annual precipitation was corre-

lated against mean grebe population in dif-

ferent seasons. No correlation was found

between annual rainfall and winter abun-

dance of grebes

= 0.05; df = 1,3; F= 0 157;

P = 0.718). The same was true of spring

abundance (R' = 0.233; df = 1,3; F = 0 157; P

= 0.718). However, a positive and significant

correlation was found between total annual

rainfall and grebe abundance in the follow-

ing spring (R2 = 0.776; df = 1,3; F = 10.363; P

= 0.049). This correlation was especially

strong because of two species, the Silver

Grebe (R2 = 0.802; df = 1,3; F = 12.127; P =

0.04) and the Pied-billed Grebe (R2 = 0.958;

df = 1,3; F = 68.898; P = 0.004) (Fig. 3.). No

correlation was found between annual rain-

fall and following spring abundance of the

Great Grebe

df = 1,3; F

0.014; P

= 0.91) and the White-tufted Grebe (R2

0.45; df = 1,3; F = 2.367; P = 0.22). The total

abundance of these grebe species shows a de-

layed response to the rainfall, especially to

the increased precipitation associated with

ENSO events.

Rainfall and habitat associations patterns

The four species differed in their distri-

bution patterns in the four habitats surveyed.

The White-tufted Grebe and especially the

Silver Grebe showed a marked tendency to

gather in two of the four habitats: Los Molles

reservoir and El Rey lagoon. The average

abundance during the 47 months of the sur-

vey was approximately 70-80 individuals for

both species while, in the other two habitats,

there were fewer than ten birds. The Great

Grebe tended to concentrate in the Los

Molles Reservoir and the Pied-billed Grebe

tended to be present in very small numbers

00

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p- r-.4

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z

0 00c 00

un

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044

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040 1> 00

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ec00 ZZ 000 0

1000

04 10 c

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0 - O

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cc 0 L

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ris

-

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98 WATERBIRDS

400 a _{- 1000}

0 0

300 o 750

0 0

-

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_o

0 0o

Eoo

o

o

"200

500

0 0

oo

100 0 0 00 o _ooa 250

J

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oa

oM

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MONTHS

Figure 2. Monthly rainfall (columns) and monthly abundance of all species of grebes (open dots) in the whole study area.

in all four habitats (Fig. 4). These habitat as-

sociation patterns showed no change during

the post-ENSO period (Table 2). Conse-

quently, the increase in grebe abundance

noted in post-ENSO years did not affect the

local distribution patterns in the wetlands.

Breeding

During the study, all four species of

grebes have been observed breeding. Great,

Pied-billed and White-tufted grebes bred

regularly in the wetlands in low numbers and

alone. The Silver Grebe formed colonies of

several hundred, nesting only during ENSO

summers and during the immediate post-

ENSO summers. These colonies were only

established in the El Rey lagoon and the Los

Molles reservoir.

DISCUSSION AND CONCLUSION

ENSO and grebes abundances

The effects of the El Nifio Southern Os-

cillation (ENSO) on grebe populations was

similar to that observed for carnivores in the

semi arid Mediterranean zone of Chile, with

a time lag response to increases in small

mammal prey species (Jaksic et al. 1997; Jak-

sic 1998). The grebes are upper trophic level

consumers in fresh water systems, feeding on

aquatic invertebrates, fish, amphibians, and

even chicks of other bird species (Del Hoyo

et al. 1992). In the present study, the delay in

abundance may also be associated with an in-

crease in prey species, as well as an increase

in breeding habitat.

"EL NIi4O" EFFECT ON FOUR GREBES SPECIES

500 1000

Podiceps occipitalis

S400 s800

300

600

200

400

0 0

200 400

1992 1993 1994 1995 1996 1997 1998

20 1000

Podylimbus podiceps

800 S15

10 5'

S200 0 400

1992 1993 1994 1995 1996 1997 1998

YEARS

Figure 3. Yearly rainfall (closed dots) and mean spring abundances (columns) of two species of grebes in the whole study area.

that of the grebes in Black-necked Swans,

(Cygnus melanocorhypha)

which breeds oppor-

tunistically in the El Rey lagoon in association

with ENSO events (Vilina et al. in prepara-

tion). The same perturbation that provokes

breeding failure in seabirds of the southern

Pacific (Araya 1987; Guerra et al. 1988; Duffy

1990; Vilina 1993; Boersma 1998) increases

breeding success in some aquatic birds in the

wetlands of central Chile, such as the Silver

Grebe and the Black-necked Swan.

ENSO and grebe habitat association

Distribution patterns of aquatic birds may

be influenced by habitat characteristics: nutri-

ents and pH (Nagarajan and Thyagesan

1996), depth and vegetation patterns (Amat

and Ferrer 1988; Barnes and Nudds 1990;

Murkin et al. 1997), prey abundance (Elmberg

et al. 1993), interspecific competitive interac-

tions (Amat 1984; Elmberg et al. 1997); or by

combinations of these factors (Dubowy 1988).

The patterns of habitat association for

the four species of grebe did not change dur-

ing ENSO or post-ENSO years, compared to

drier years. These patterns were also season-

ally stable (data not presented). The habitats

25 -20

Podiceps major Podylimbus podiceps 20

1515

10 1

40

40

Co

20

0 10

El Rey Los Molles Stream Coastal lagoon El Rey Los Molles Stream Coastal lagoon

120

Podiceps occipitalis 120 Rollandia rolland

U 100 100

060

0

El Rey Los Molles Stream Coastal lagoon El Rey Los Molles Stream Coastal lagoon

100 WATERBIRDS

Table 2. Distribution of grebes abundances (individuals per site) through the study habitats in the Estero El Yali wet- land. The expected value of abundance was calculated according to the total species abundance and the area of the habitats. Observed and expected values were compared using a chi-square goodness of fit test (Sokal and Rolf 1995).

Coastal

El Rey Los Molles Stream _{Lagoon X2} P

Period I: 1993 and 1998 White-tufted Grebe

Obs. Freq. 1520 1125 0 29 1500 <0.0001 Exp. Freq. 855.7 695.2 775.5

Silver Grebe

Obs. Freq. 1788 1738 0 0 0.709 <0.399 Exp. Freq. 1764 1764

Pied-billed Grebe

Obs. Freq. 10 75 13 7 117.9 <0.0001

Exp. Freq. 33.5 27.3 13.7 30.5 Great Grebe

Obs. Freq. 34 165 34 23 208.6 <0.0001

Exp. Freq. 82 66.6 33.3 74

Period II: 1994-1997 White-tufted Grebe

Obs. Freq. 1455 2481 16 199 3175.9 <0.0001 Exp. Freq. 1328 1080 540 1203

Silver Grebe

Obs. Freq. 636 1752 0 0 521.5 <0.0001 Exp. Freq. 1194 1194

Pied-billed Grebe

Obs. Freq. 5 17 5 20 12.04 <0.0001

Exp. Freq. 15 12.2 6.1 13.6

Great Grebe

Obs. Freq. 114 432 64 136 394.4 <0.0001 Exp. Freq. 238.7 194 90 216

most used by the grebes were El Rey lagoon

and Los Molles reservoir. These habitats had

the greatest cover of emergent, floating or

submerged vegetation. Moreover, such habi-

tats were the most eutrophic, yet they had

some open water, presenting a mix of pro-

tected and open habitats that are elsewhere

the preferred habitat for aquatic birds such

as coots, dabbling and diving ducks (Murkin

et al. 1997). Furthermore these characteris-

tics (abundant vegetation and open water)

are very important in the selection of breed-

ing habitat by other grebe species (Chabreck

1963; Burger 1974; Nudds 1982; Boe 1994).

ACKNOWLEDGMENTS

We would like to especially thank M. D. Garcia, C. Silva-Garcia, J. Meza, J. Rottmann, M. V. L6pez-Calleja, P. Farias and the waterfowl group of UNORCH (The Or- nithologist Union of Chile), for their field assistance

and support, and P. Canevari of Wetlands for the Amer- icas and P. Hicklin of the Canadian Wildlife Service for their support. H. Cofr6 is currently supported by a CONI- CYT (Comisi6n Nacional de Desarrollo Cientifico y Tec- nol6gico) Doctoral Fellowship.

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