Abundance and Phenology of Red Knots in the Guerrero Negro–Ojo

10 Wader Study Group Bulletin 115 (1) 2008 Abundance and phenology of Red Knots in the Guerrero Negro–Ojo de Liebre coastal lagoon complex, Baja California Sur, Mexico ROBERTO CARMONA1, NALLELY ARCE1, VÍCTOR AYALA-PÉREZ1 & GUSTAVO D. DANEMANN2 1Marine Biology Department, Universidad Autónoma de Baja California Sur. Apartado postal 19-B, La Paz, Baja California Sur, CP 23000 Mexico 2Bird Conservation Program, Pronatura Noroeste A.C. Calle Décima No60, Ensenada, Baja California, CP 22800 Mexico Carmona, R., Arce, N., Ayala-Pérez, V. & Danemann, G.D. 2008. Abundance and phenology of Red Knots in the Guerrero Negro–Ojo de Liebre coastal lagoon complex, Baja California Sur, Mexico. Wader Study Group Bull. 115(1): 10–15. Keywords: Red Knot, Calidris canutus roselaari, migration, Ojo de Liebre lagoon, Guerrero Negro lagoon, saltworks, Baja California, Mexico To determine the spatial and temporal distribution of Red Knots Calidris canutus roselaari in the Guerrero Negro–Ojo de Liebre coastal lagoon complex, including the Guerrero Negro Saltworks, we carried out a monthly census from July 2006 to June 2007. The aggregate total of the twelve monthly counts was 32,059, and the maximum count of 6,458 was made in September 2006. The Red Knots arrived in July and August and their numbers were high until October, decreased in November and increased again in December (to 4,595), but then declined constantly until March; in April there was a notable increase to 4,647. We suggest two hypotheses to explain the fluctuations in numbers: (1) that there is onward migration with birds departing in late autumn and more birds arriving for the winter or (2) that Guerrero Negro is the terminus of the migration and numbers vary because of local movements to and fro other sites within a 200 km radius. Seventy-seven per cent of all knots counted occurred in 11 of the 45 zones into which we divided the study area. We classified the 11 zones into four sections according to their seasonal use by the knots: Los Medanitos was important in autumn; Estero Norte in spring; Guerrero Negro was consistent and with regular abundance throughout the year; and Salitrales showed large fluctuations. We conclude that the abundance of knots in these four sections can be used to estimate the total number in the entire lagoon/saltworks complex (r2 = 0.94). INTRODUCTION In Baja California, 1,053 knots were counted at Guerrero Negro in Jan 1994 (Page et al. 1997), but it was not until The Red Knots Calidris canutus that migrate along the Pacific 2005 that relatively larger numbers were recorded there. In coast of North and Central America belong to the roselaari Oct 2005, Carmona et al. (2006) counted 2,907 knots near subspecies which breeds on Wrangel Island and in west Guerrero Negro in the ESSA saltworks alone. There the birds Alaska (Tomkovich 1992). Confirmation of this connectivity were using a low-salinity concentration pond known as Sali- came in Oct 2007 when one knot was seen at Guerrero Negro, trales 1A (S-1A, Fig. 1) which is an atypical habitat for knots Baja California, Mexico, that had been marked on Wrangel being non-tidal. More typical knot habitat exists nearby in the Island during the previous breeding season and two birds were form of the tidal Ojo de Liebre and Guerrero Negro Lagoons seen that had been marked in W Alaska in May 2006 (P.S. (Fig. 1). Therefore in order to establish the true importance Tomkovich, B.A. Harrington, pers. comm.). Similarly four of the Guerrero Negro area for knots, we carried out monthly knots were seen on the coast of Washington and two in W counts in all potential knot habitat throughout the annual cycle Alaska in May 2007 that had been marked at Guerrero Negro between July 2006 and June 2007. in Oct 2006 (Buchanan 2007, R. Gill, pers. comm.). As we plan to continue monitoring the Guerrero Negro Although large numbers of knots (>100,000) were knot population and as coverage of such a large area is occasionally recorded in Alaska during May 1975–1980, at logistically difficult, a secondary aim of our fieldwork was to no time have similar numbers been recorded further south identify the key areas used by knots so that a strategy could along the American Pacific coast where it is thought that be devised that would allow future surveys to be conducted all roselaari spend the winter. Therefore many of the birds more efficiently. seen in Alaska may have been rogersi, the subspecies which breeds in E Siberia and winters in Australasia (Morrison et al. METHODS 2006). Numbers reported along the Pacific coast of the United States from Washington to California and in Mexico suggest a The study area is in the Sebastian Vizcaíno Bay on the west population that has never exceeded 10,000 (Page et al. 1999). coast of the Baja California peninsula, NW Mexico (Fig. 1). Moreover reports from stopover sites in Washington suggest It includes two coastal lagoons: the Guerrero Negro La- that the population has declined significantly in recent years goon (2,100 ha) and the Ojo de Liebre Lagoon (57,100 ha; (Buchanan 2006, 2007). Lluch-Cota et al. 1993). The Guerrero Negro saltworks are 10 Carmona et al.: Red Knots in coastal lagoon complex, Mexico 11 Mexico Guerrero Guerrero Negro Negro Lagoon 28º 28º00' Sea of Cortez N Pacific Ocean 1 Guerrero Negro Pacific Ocean Town 24º 110º Ojo deLagoon Liebre ESSA 2 27º42' 3 4 Concentration Areas S-1A N 0 7 km 114º11' Fig. 1. The study area at Guerrero Negro, Baja California, Mexico. The areas surveyed are shown in dark grey and light grey. The four key sections shown in dark grey are: (1) Guerrero Negro, (2) Estero Norte, (3) Los Medanitos, and (4) Salitrales. The “Others” section is shown in light grey (see text). located adjacent to the latter, encompassing 33,000 ha of RESULTS artificial wetlands (Danemannet al. 2002; Fig. 1). The three wetlands are surrounded by the Vizcaíno Desert, and are part We recorded an aggregate total of 32,059 Red Knots in the 12 of the “El Vizcaino” Biosphere Reserve, a federal protected monthly counts (Table 1). The first migrants had arrived by area. The climate of the region is arid, with winter rains that the time of our July count, but numbers increased strongly in are <100 mm annually (Salinas-Zavala et al. 1991). August and remained high until November when there was For the purposes of our census of Red Knots, we divided the Guerrero Negro and Ojo de Liebre lagoons into 12 and 21 zones, respectively. We based these divisions on substrate Table 1. Monthly counts of Red Knots in different sections of the type (muddy, sandy, or salt marsh) and whether they were Guerrero Negro–Ojo Liebre coastal lagoon complex, including the natural or artificial (see Appendix). The saltworks are divided Guerrero Negro saltworks, between July 2006 and June 2007) into 18 concentration ponds with salinities between 35 and Month Counting sections Total 250‰; only the 12 ponds with lower salinity are used by birds Salitrales Guerrero Estero Los Others (Carmona & Danemann 1998). Negro Norte Meda We carried out the census monthly between July 2006 and nitos June 2007 covering the entire area shaded light grey and dark Jul 5 0 2 180 213 400 grey in Fig. 1. Each count took five days to complete by two Aug 837 111 0 1,697 1,967 4,612 teams of two or three people. We used flatbed trucks (along Sep 4,705 315 204 70 1,164 6,458 the roads and levees that separate the concentration ponds, Oct 3,877 336 97 0 1,560 5,870 and a few coastal portions of the Guerrero Negro Lagoon), Nov 897 395 157 0 1,189 2,638 Dec 3,786 428 30 0 351 4,595 all terrain vehicles (to cover the salt marshes and wetland Jan 1,046 228 122 68 294 1,758 flats in the western portion of the Ojo de Liebre Lagoon), and Feb 169 301 0 0 430 900 motor boats (to cover the channels and coastal zones of both Mar 108 0 10 5 3 126 lagoons) (Appendix). We carried out all surveys as close to Apr 337 27 3,720 365 198 4,647 the shoreline as possible. May 0 0 0 0 29 29 We counted birds in flocks of <300 individually and esti- Jun 0 0 0 26 0 26 mated the size of larger flocks using the methods suggested Aggregate 15,767 2,141 4,342 2,411 7,398 32,059 total by Kasprzyk & Harrington (1989). We used 10× binoculars and 15–60× telescopes. 12 Wader Study Group Bulletin 115 (1) 2008 Fig. 2. Monthly abundance of Red Knots in counting sections of the Guerrero Negro–Ojo Liebre coastal lagoon complex, including the Guerrero Negro Saltworks, between July 2006 and June 2007. a 45% decrease (Fig. 2). In December, numbers increased The abundance of knots in the 11 priority zones proved to again, followed by a fairly constant decrease until March. be highly correlated with total abundance in the study area Another substantial peak occurred in April with numbers (F1,9 = 135.5, P < 0.001), explaining 94% of the observed comparable to those of August–October and December. In variation (Fig. 3). May and June, only small numbers remained. Our data showing the spatial distribution of the birds DISCUSSION allowed us to identify 11 key zones for Red Knots in which future studies might be concentrated. We grouped these into These results show that, with a peak count of 6,458 (more four sections: Salitrales, Estero Norte, Los Medanitos and than double the previous record count for Mexico), Guerrero Guerrero Negro; all other counting zones were included in a Negro is the most important known site for roselaari Red fifth section (“Others”) (Table 1).

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