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). Knots south of Alaska. They also indicate that the birds use The 11 key zones accounted for 77% of the aggregate the area during both autumn and spring as well as in winter. birds counted. The most important were Salitrales (50% of Even if there is little turnover, it would seem that by far the records, Table 1), which includes part of the Guerrero Negro majority of the roselaari population uses Guerrero Negro at saltworks and the Ojo de Liebre Lagoon, followed by Estero some time during the year. Norte (13.5%), Los Medanitos (7.4%) and Guerrero Negro (6.7%) (Fig. 1). How accurate are the counts? The pattern of use of each section was different over time 2 (χ 40 = 35.6; p < 0.01). Los Medanitos was used most at the Ideally, shorebirds should be counted simultaneously across beginning of the autumn migration (July and August) but a whole site, preferably when they are concentrated at high barely used during the rest of the year, except for a small tide. At such a huge site as Guerrero Negro that would re- increase in spring (Table 1). In contrast, numbers in Estero quire a very large number of observers that are simply not Norte were low in autumn and winter, but it was the most available. Therefore, with our limited resources, we had to important site in spring, when 80% of the 4,647 Red Knots conduct each monthly count over five days using two teams occurred there (Table 1). counting throughout the day and therefore throughout the With a maximum count of only 430 the Guerrero Negro tidal cycle. This method would have led to inaccurate counts section had relatively low numbers, but they showed the if significant numbers of knots moved from place to place; least fluctuation (Table 1). In contrast, numbers at Salitrales either we might have counted some birds more than once or showed noticeable fluctuations and (except for April) deter- we might have missed them altogether. mined the overall abundance pattern for the entire coastal Although we accept that there could be some inaccura- lagoon complex. This section held the highest numbers in cies in our counts for these reasons, we do not consider that autumn (September and October) and in winter (December), they will have led to significant error. Generally the knots with a noticeable decrease in November. In the “Other” zones, at Guerrero Negro seem to be very site-faithful. If we see a Red Knots were dispersed, even though as a group they flock in one place one day, we can normally expect to see a ­accounted for 23% of the aggregate count (Table 1). similar-sized flock in the same place over the next several Carmona et al.: Red Knots in coastal lagoon complex, Mexico 13

7000 Total count = 268 + 1.17(Count in priority sections) 6000 R-sq = 0.94

5000

4000

3000

2000 Total count all sections 1000

0 0 1000 2000 3000 4000 5000 6000 Count in four priority sections

Fig. 3. Counts of Red Knots in the whole of the study area at Guerrero Negro (the Guerrero Negro and Ojo de Liebre lagoons and the ­Exportadora de Sal saltworks) plotted against the combined counts for the four priority sections (Los Medanitos, Estero Norte, Guerrero Negro and Salitrales). days. Moreover there is now evidence from individually in- et al. 2003, Maimone-Celorio & Mellink 2003, Palacios et scribed flag resightings that knots are also very site-faithful al. 1991, Zárate et al. 2006) suggest that such within-winter within the Guerrero Negro area between years (H.P. Sitters, movements may be limited to sites quite close to Guerrero pers. comm.). Negro; particularly the Manuela, San Ignacio, La Bocana and El Coyote coastal lagoons, all on the Pacific coast between What are the reasons for the fluctuating numbers? 28°15' and 26°25'N and no more than 200 km away. The terminus hypothesis is also supported by the fact that There could be two rather different explanations for the birds caught at Guerrero Negro around the end of October monthly patterns of abundance we observed: 2006 gave no indication that they were laying down resources for onward migration. Of 130 adults caught between 24 Oct l The onward migration hypothesis: The autumn peak and 1 Nov 2006, 90 had finished their primary moult (and represents mostly passage migrants that move on to winter were heavier than those still in active primary moult) and probably further south; more birds arrive for the winter had an average weight of 133.8 g (SD = 10.4) which is very leading to the December peak and in April there is a return similar to knots caught in mid-winter in Florida (females: passage, or 138.7, males: 130.0, Niles et al. 2007) and far less than knots preparing for onward migration in Patagonia (161.1 g, l The terminus hypothesis: The Guerrero Negro area is ­Harrington et al. 2007). effectively the terminus of the roselaari migration and all It should be noted that the onward ­migration and terminus the fluctuations we observed are caused by birds moving hypotheses are not mutually exclusive: part of the fluctua- between Guerrero Negro and other relatively local sites tion we observed could be the result of migration, part local (within say 200 km). movement. The two hypotheses also have major implications for estimates of the total number of individual knots that use As yet there is no clear proof of either hypothesis, but the Guerrero Negro during the year. If there is onward migra- terminus hypothesis would seem to be the most strongly tion, the birds present in October may be largely replaced in supported by available information. Records of knots further December and turnover may mean that the total throughput south along the Pacific coast, in southern Mexico, Central and is large. On the other hand if Guerrero Negro is the migration South America are scarce (Johnson 1965, Morrison & Ross terminus, total numbers may be no more than our maximum 1989) and do not indicate wintering sites, so if the knots that count of 6,458. visit Guerrero Negro in autumn move on to winter elsewhere, their destination is unknown. Given the surveys that have Spatial and temporal distribution of knots at been carried out over the years and the large numbers of bird- Guerrero Negro watchers that visit the Pacific coast, it would seem unlikely that several thousand knots have been overlooked. The temporal distribution pattern differs between the natural Most shorebird populations remain at their wintering sites and the artificial habitats. The latter (saltworks) is important for at least three months, usually December, January and only during autumn, as reported by Carmona et al. (2006), February (e.g. Aparicio 2006, Barbieri 2007). However our while natural sites are used throughout the year, including counts fluctuated widely over this period (from 4,595 to 1,758 winter, as reported by Page et al. (1997) and Patten et al. to 900, Table 1). Therefore this may result from local move- (2003), in relation to the wintering shorebirds of the region ments between Guerrero Negro and other nearby wetlands, generally. as reported for Western Sandpipers Calidris mauri in other The 11 priority zones are all intertidal mudflats and marsh- areas of the Baja California peninsula (Brabata 2000, Fernán- es (Appendix 1), where the Red Knots presumably feed dez et al. 2001). In the case of knots, the few records for the during low tide and roost over high tide (Harrington 2001, northern and southern wetlands of Baja California (Carmona Helseth et al. 2005). The only artificial zone of importance 14 Wader Study Group Bulletin 115 (1) 2008 for knots is the S1-A evaporation lagoon in the saltworks, a Buchanan, J.B. 2007. Observations of Red Knots Calidris canutus in coastal large, low-salinity wetland that offers feeding conditions that Washington, USA: the 2007 spring migration. Wader Study Group Bull. are similar to the natural intertidal mudflats nearby in the Ojo 114: 65–66. Buenrostro, M.A., N. Warnock & H. de la Cueva. 1999. Wintering West- de Liebre Lagoon (Carmona et al. 2006). ern Sandpipers Calidris mauri at Estero Punta Banda, Baja California, The three priority sections located around the Ojo de México. Wader Study Group Bull. 88: 59–63. ­Liebre Lagoon showed the highest abundances and the Butler, R.W., R.C. Ydenberg & D.B. Lank. 2003. Wader migration on the greatest temporal fluctuations. In Los Medanitos the largest changing predator landscape. Wader Study Group Bull. 100: 130–133. numbers were recorded in autumn, in Estero Norte in spring Carmona, R. & G. Danemann. 1998. Distribución espaciotemporal de aves and in Salitrales in winter and autumn, indicating that the en la Salina de Guerrero Negro, Baja California Sur, México. Ciencias Marinas 24: 389–408. birds use different parts of the study area during the year. This Carmona, R., D. Galindo & L. Sauma. 2003. New and noteworthy shore- could be related to changes in the availability and abundance birds records from South Baja California Peninsula, Mexico. Wader Study of food or in the risk of predation (Bryant 1979, Butler et al. Group Bull. 101–102: 62–66. 2003, Colwell & Landrum 1993, Evans 1976). In contrast, the Carmona, R., V. Ayala-Pérez, N. Arce & L. Morales-Gopar. 2006. Use low and relatively stable numbers observed in the Guerrero of saltworks by Red Knots at Guerrero Negro, Mexico. Wader Study Negro section may indicate either birds that choose to stay Group Bull. 111: 46–49. Colwell, M.A. & S.L. Landrum. 1993. Nonrandom shorebird distribution in one area and defend a feeding territory (Recher & Recher and finescale variation in prey abundance.Condor 95: 94–103. 1969), or relatively inexperienced or subdominant birds using Danemann, G., R. Carmona & G. Fernández. 2002. Migratory shorebirds suboptimal habitat (Buenrostro et al. 1999); further observa- in the Guerrero Negro Saltworks, Baja California Sur, Mexico. Wader tions need to be made to test these hypotheses. Study Group Bull. 97: 36–41. Evans, P.R. 1976. Energy balance and optimal foraging strategies in shore- birds: some implications for their distributions and movements in the Future fieldwork non-breeding season. Ardea 64:112–139. Fernández. G., H. de la Cueva & N. Warnock. 2001. Phenology and length We plan to continue monitoring the Red Knot population of of stay of transient and wintering Western Sandpipers at Estero Punta Guerrero Negro but limiting our effort to the key sites identi- Banda, Mexico. J. Field Ornithol. 72: 509–520. fied in 2006/7 in order to improve efficiency. Nevertheless we Harrington, B.A. 2001. Red Knot (Calidris canutus). In: The Birds of North are aware of the dangers of basing our methods on just one America A. Poole (ed.) 563: 1–32. year’s data and will monitor other sites from time to time. Harrington, B.A., B. Winn & S.C. Brown. 2007. Molt and body bass of red We also plan to survey other potential knot habitat within knots in the eastern United States. Wilson J. Ornithol. 119: 35–42. Helseth, A., Å. Lindström & M. Stervander. 2005. Southward migra- 200 km of Guerrero Negro in order to evaluate the terminus tion and fuel deposition of Red Knots Calidris canutus. Ardea 93: and onward migration hypotheses and to monitor the pres- 213–224. ence of the individually marked birds to establish whether Johnson, A.W. 1965. The Birds of Chile. Vol. 1. Platt Establecimientos and when they leave the area. Graficos S. A., Buenos Aires. Kasprzyk, M.J. & B.A. Harrington. 1989. Manual de Campo para el Estudio de Playeros. Manomet Bird Observatory (MBO). Ensenada, ACKNOWLEDGEMENTS B.C. Mexico. Lluch-Cota, D.B., A. Castellanos-Vera, J. Llinas-Gutiérrez & A. Ortega- We thank Exportadora de Sal S.A. de C.V (ESSA) and all Rubio. 1993. La Reserva de la Biósfera del Vizcaíno. In: S. Salazar- its staff, especially E. Elorduy, M. Domínguez, M. García, Vallejo y N. E. González (eds). Biodiversidad Marina y Costera de R. Zaragoza and F. Castillo for their logistic support both México. CONABIO-CIQRO, México, DF. pp. 358–388. in the field and in their hosting facility. We also thank the Maimone Celorio, M.R. & E. Mellink. 2003. Shorebirds and benthic fauna Aquatic Birds Lab personnel from the Universidad Autónoma of tidal mudflats in Estero Punta Banda, Baja California, México. Bull. de Baja California Sur for their assistance in the field. This S. California Acad. Sci. 102: 26–38. Morrison, R.I.G., B.J. McCaffery, R.E. Gill, S.K. Skagen, S.L. Jones, research is part of the project entitled “Conservation of the G.W. Page, C.L. Gratto-Trevor & B.A. Andres. 2006. Population Brants (Branta bernicla) and other migratory waterbirds in estimates of North American shorebirds, 2006. Wader Study Group the Guerrero Negro–Ojo de Liebre coastal lagoon complex”, Bull. 111: 67–85. funded by the North American Wetland Conservation Act by Morrison, R.I.G. & R.K. Ross. 1989. Atlas of Nearctic shorebirds on the means of the Mexico Program of the Division of Bird Habitat coast of South America. Can. Wildl. Serv. Spec. Publ. vol. 1–2. Conservation of the United States Fish and Wildlife Service, Niles, L.J., H.P. Sitters, A.D. Dey, P.W. Atkinson, K.A. Bennett, K.E. Clark, N.A. Clark, C. Espoz, P.M. González, B.A. Harrington, D.E. coordinated by E. Murphy. B.A. Harrington, N.A. Clark and Hernandez, K.S. Kalasz, R. Matus, C.D.T. Minton, R.I.G. Morrison, H.P. Sitters reviewed an earlier version of this paper, and M.K. Peck & I.L. Serrano. 2007. 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Appendix

The 45 zones of the study area at Guerrero Negro, Baja California, Mexico (LOL = Laguna Ojo de Liebre, LGN = Laguna de Guerrero Negro, ESSA = Exportadora de Sal saltworks), with details of environment type, priority section (see text) and the means by which by which each was counted.

Zone Environment type Priority Counted Zone Environment type Priority Counted section from section from ESSA-A1 Artificial Others Car LOL-01 Sandy Beach & Salt Marsh Others ATV ESSA-A2 Artificial Others Car LOL-02 Sandy Beach Others ATV ESSA-A3 Artificial Others Car LOL-03 Muddy Beach & Salt Marsh Others ATV ESSA-A4 Artificial Others Car LOL-04 Sandy Beach & Salt Marsh Others ATV ESSA-A5 Artificial Others Car LOL-05 Salt Marsh Others Boat ESSA-A6 Artificial Others Car LOL-06 Sandy Beach & Salt Marsh Estero Norte Boat ESSA-A7 Artificial Others Car LOL-07 Muddy Beach & Salt Marsh Estero Norte Boat ESSA-A8 Artificial Others Car LOL-08 Sandy Beach & Salt Marsh Others Boat ESSA-A9 Artificial Others Car ESSA-S1A Artificial Salitrales Car LOL-09 Sandy Beach Los Medanitos Boat ESSA-S1B Artificial Others Car LOL-10 Muddy Beach & Salt Marsh Los Medanitos Boat ESSA-S2 Artificial Others Car LOL-11 Muddy Beach Others Boat LOL-12 Sandy Beach Salitrales Boat LGN-01 Artificial Others Car LOL-13 Salt Marsh Salitrales Boat LGN-02 Artificial Others Car LOL-14 Sandy Beach & Salt Marsh Salitrales Boat LGN-03 Artificial Others Car LGN-04 Muddy Beach & Salt Marsh Guerrero Negro ATV LOL-15 Sandy Beach & Salt Marsh Salitrales Boat LGN-05 Muddy Beach & Salt Marsh Guerrero Negro ATV LOL-16 Sandy Beach Others Boat LGN-06 Salt Marsh Others Car LOL-17 Sandy Beach Others Boat LGN-07 Sandy Beach & Salt Marsh Others Boat LOL-18 Sandy Beach Others Boat LGN-08 Muddy Beach Others Boat LOL-19 Sandy Beach & Salt Marsh Others Boat LGN-09 Sandy Beach & Salt Marsh Others Boat LOL-20 Sandy Beach Others Boat LGN-10 Sandy Beach & Salt Marsh Others Boat LOL-21 Artificial Others Boat LGN-11 Sandy Beach Others Boat LGN-12 Salt Marsh Others Boat