Jorge H. Vega Rivera

Modelling the potential winter distribution of the endangered Black-capped Vireo ( Vireo atricapilla )

We applied the ecological niche/habitat modelling approach to predict the potential winter distribution of the endangered Black-capped Vireo Vireo atricapilla. We used historical and current field records along with climatic and topographic variables to generate three different models (Biomapper, Maxent, and GARP). Using field data on species occurrence, a model was selected based on the accuracy of assessment results. A final model was obtained by eliminating those areas mapped as known unsuitable habitat, using high resolution land use/land cover data. The GARP model obtained the best accuracy values. It showed the winter distribution of the Black-capped Vireo to cover an area in western Mexico of about 141,000 km that runs along the Pacific coast from southern Sonora (Rı́o Yaqui, Alvaro Obregón Dam) to the southern state of Oaxaca (Salina Cruz on the Pacific coast and Matias Romero, and inland). One third of the proposed model’s area was located at elevations of 0–500 m, while 83% occurred at elevations , 1,250 m; however, a significant area (17%) consists of sites . 1,250 m in elevation. For the most part, the distribution model proposed closely followed the tropical dry forest boundaries and clearly avoided temperate areas at higher elevations. This situation seems to be critical for the species, since the dry forest is one of most endangered Neotropical ecosystems, both nationally and internationally. Furthermore, the array of areas under protection regimes included only about 7.1% of the predicted wintering area. However, this figure could be misleading when it is considered that some protected areas are just ‘‘paper reserves’’ without significant conservation programmes developed in situ.

PHENOLOGY, HABITAT USE, AND NESTING OF THE RED-BREASTED CHAT (GRANATELLUS VENUSTUS)

Abstract From March 1999 to August 2000, we conducted monthly mist netting in the Chamela-Cuixmala Biosphere Reserve, Jalisco, Mexico to document the phenology and habitat use of the Red-breasted Chat (Granatellus venustus). We collected information on its nesting biology during the breeding season of 2001. Chats (n = 116) were caught throughout the 18 months of the study; however, far fewer captures occurred during the dry season than during the wet season. Our capture data revealed that chats made greater use of deciduous (n = 88) than semi-deciduous forest (n = 28); there were no interactions among forest type, season, and gender. Birds in breeding condition were captured June–September and molting birds were captured August– October. We found 10 cup-shaped nests in June and July. Nests were 48–103 cm above ground in saplings ≤2 m high. Clutch size was 3–4 and only the female incubated. The incubation period was 14 days, and we estimated the nestling period to be approximately 8–10 days. Of eight nests found with eggs or young, three were depredated during the egg stage, three during the nestling stage, and two were successful.

FIRST REPORT OF COWBIRD PARASITISM ON THE BLACK-CAPPED GNATCATCHER IN WESTERN MEXICO

Abstract Information on cowbird parasitism in Mexico is rare. We report the successful fledging of a brown-headed cowbird (Molothrus ater) nestling by black-capped gnatcatchers (Polioptila nigriceps) in the tropical deciduous forest of the Chamela-Cuixmala Biosphere Reserve, western Mexico, in June 2001. We observed 2 additional gnatcatcher pairs feeding a single brown-headed cowbird fledging. Opportunistic observations of nests of other species and few captures of brown-headed cowbirds during 18 months of intensive mistnetting suggested that cowbird abundance and parasitism was low in the reserve.

NESTING RECORD AND POPULATION PHENOLOGY OF THE FLAMMULATED FLYCATCHER (DELTARHYNCHUS FLAMMULATUS)

Abstract We used mist netting in the Chamela-Cuixmala Biosphere Reserve to assess the population phenology of the Flammulated Flycatcher (Deltarhynchus flammulatus), a poorly-known dry forest endemic of the Mexican Pacific Slope. We captured 135 birds (first records only) during 23,515 net hrs over a period of several years which suggests this flycatcher is common at the reserve. Monthly averages of captures (including monthly recaptures) differed between seasons with a peak (71%) during May to August (end of dry season to middle of wet season) and fewer (29%) captures during the rest of the year. Flammulated Flycatchers in breeding condition (n  =  38) were captured in June and July. Hatching year birds (n  =  8) were captured from 10 July through 11 December. We found an active nest in a cavity on 29 June 2010. We observed pieces of snake skin lining the nest, which may indicate a closer relationship with Myiarchus. Additional knowledge on the ecology and breeding biology of the Flammulated Flycatcher is urgently needed for development of effective conservation plans.

RESPONSE OF BIRDS IN TROPICAL DECIDUOUS FOREST TO BROWN-HEADED COWBIRDS (MOLOTHRUS ATER)

Abstract During June–September 2007, we searched bird nests for evidence of parasitism by brown-headed cowbirds (Molothrus ater) and we tested response of the avian community to taxidermy mounts of a brown-headed cowbird in a tropical deciduous forest in the Chamela-Cuixmala Biosphere Reserve in western Mexico. Of 46 nests found (black-capped gnatcatcher Polioptila nigriceps, 2; red-breasted chat Granatellus venustus, 1; blue bunting Cyanocompsa parellina, 1; orange-breasted bunting Passerina leclancherii, 1; rufous-backed thrush Turdus rufopalliatus, 1; yellow-green vireo Vireo flavoviridis, 39), only one was parasitized (nest of a black-capped gnatcatcher). Experimental responses to taxidermy mounts suggested that yellow-green vireos may have had previous contact with cowbirds. We conclude that in the Chamela-Cuixmala Biosphere Reserve, parasitism by brown-headed and bronzed cowbirds (Molothrus aeneus) remains low, or even absent for some species, as on the yellow-green vireo, but this situation could change in the near future because significant developments for the tourism industry are planned adjacent to the reserve; that could create new habitat and sources of food for cowbirds.