Movement patterns of granivorous birds in relation to seed abundance in the central Monte desert, Argentina

CUETO, V. R.; SAGARIO, M.C.; LOPEZ DE CASENAVE, J.; HERWIG, E.

Campos do Jordao

Congreso; XXV International Ornithological Congress; 2010

Movement Patterns of granivorous birds in relation to seed abundance in the central Monte desert, Argentina Cueto VR, Sagario MC, Lopez de Casenave J & Herwig E ECODES (Grupo de Investigación en Ecología de Comunidades de Desierto/ Desert Community Ecology Research Team). Departamento de Ecología, Genética y Evolución, FCEyN, Universidad de Buenos Aires, Argentina. - e-mail: tatysagario@ege.fcen.uba.ar In the central Monte desert, grass seeds constitute 80% of granivorous birds’ diet. This strong dependence may have important effects on the dynamics of these birds, which may vary with their ecological strategies. We seasonally mist-netted birds at Ñacuñán Reserve and estimated grass seed abundance during five years (2005-2009). We assessed movement patterns of granivorous species and their variation in number of captures during winter (maximum seed consumption). We found a continuous range of movement patterns in four granivorous populations. We relocated 40.4% of the many-colored Chaco finch (MCCF) individuals, and observed lower values for the ringed warbling finch (RWF: 18.5%), the resident population of rufous-collared sparrow (RCS: 12.2%) and the migratory population of the RCS (mRCS: 2.6%). Seed production showed low year-to-year variation in 2005-2008 (CV: 15.2%; Mean: 13340 seeds/m2) but dramatically decreased during 2009 (494 seeds/m2). Although fluctuations in the number of captures during winter in 2005-2008 for the most sedentary species was also low (CV: 7.1%, Mean: 0.011 captures/net-hour) we found high variation for RWF (CV: 58.7%, Mean: 0.030 captures/net-hour), RCS (CV: 50.2%, Mean: 0.071 captures/net-hour) and mRCS (CV: 59.9%, Mean: 0.032 captures/net-hour). Notwithstanding, these populations had a marked decrease in their capture number during 2009 (captures/net-hour were zero, 0.003, 0.012 and zero for MCCF, RWF, RCS and mRCS, respectively). Our results suggest that highly sedentary birds have a closer relationship with local resources and low fluctuations in their local abundance, in contrast to the more mobile ones. Less sedentary and wandering birds abundances may be restricted by resource variations at broader scales in space and time, as is usually observed in arid regions. However, in years of extremely low seed abundance birds could be equally affected - independently of their movement pattern.