Scherer and Petry • SEASONAL VARIATION IN SHOREBIRD ABUNDANCE 
41 
0 15 30 6Q 
Mostardas 
Lagoa do Peixe National Park 
51WW 
Balneario Pinhal 
-f 
PARAGUAY 
BRAZIL 
L-'v 
1 \ 
S - 
f ( 
J 
ARGENTINA J* 
/ 
RO GRANDE DO SUL TOMES 
BAI MiAMpmUAI 
1 ■ 
URUGUAY 
-\ 
•y 
. \. 
\ «_ <- V-. 
j/ 
Legend 
Lakes 
Agriculture 
Urban area 
Dunes and Fields 
Forest 
-31 ws 
—i- 
J9-OCTW 
Tk J . I, Transect (120 km) of study area between municipalities of Balnedrio Pinhal (30 J 14'57' S. 050 13 48.4 W) 
and Mostardas (31 10' 52" S. 050 50’ 03” W) on the coast of Rio Grande do Sul. southern Brazil. 
METHODS 
S'/u/v Area .—We studied shorebirds along the 
coast °I the State of Rio Grande do Sul (southern 
Brazil) between the municipalities of Mostardas 
1,1 the south (31 10' 52" S. 050 50' 03" W) and 
Balneario Pinhal in the north (30 14' 51" S. 050 
1 48.4” W), totaling 120 km of beach (Fig. I). 
The area is characterized by large sandy beaches 
dlul Stines with a series of coastal lakes beyond 
!i >e dunes (Belton 2000). Human occupation along 
'his region has altered the landscape, which is 
US «J (or tourism and recreation. Fifteen kilome- 
,ers °f shoreline in Balneario Pinhal are highly 
urbanized and the entire region is used intensively 
lor irrigated crops and tree plantations. 
The climate of the region is wet subtropical 
VVl| h a mean temperature of 17 C and annual 
'ainfall of 1.200 mm. The width of the 120-km 
s, reteh of beach ranges from 50 to 120 m. at times 
reaching 200 m. The beach has a low slope and 
'he wash zone is broad, generally -10 m with 
a high density of invertebrates. The dominant 
species are bivalve mollusks including yellow 
clams (Mesodesma mcictroides) and wedge clams 
(Donax hanleyamis), crustaceans such as mole 
crabs (Enterita brasiliensis) and cirolanid isopods 
(Excirolana armata), and polychaetes (Euzonus 
furciferus and Spin gaucha) (Gianuca 1983). 
Surveys.— Monthly surveys (n = 24) were 
conducted between October 2007 and September 
2009 along the 120 km of beach in an automobile 
traveling from north to south at a maximum speed 
of 20 km/hr between 0700 and 1700 hrs. Direct 
counts were made of the individuals of each spe¬ 
cies (Bibby et al. 2000). Surveys were conducted 
by two observers on randomly chosen sunny days. 
Shorebird abundance was recorded at a distance 
(50 to 100 m) to keep birds from Hushing. The 
first observer recorded the birds from the edge of 
the water to the middle portion of the beach and 
the second observer recorded the birds from this 
portion to the dunes, taking care to avoid recounts. 
Data were recorded on a portable voice recorder 
and field spreadsheets. Birds were identified with 
