Livestock grazing effects on flocks of seed-eating birds in the central Monte desert

ZARCO, AGUSTIN; CUETO, VÍCTOR; SAGARIO, M.CECILIA; MARONE, LUIS

CANADIAN JOURNAL OF ZOOLOGY

NATL RESEARCH COUNCIL CANADA-N R C RESEARCH PRESS

Año: 2019 vol. 97 p. 606 - 611

0008-4301

Animal populations often declineowed to habitat disturbance, but the initial response of organisms to humaninduced environmental change is usually behavioral. Intra and interspecificinteractions can restrict access to resources, changing individual fitness, andresource depletion may affect the frequency and strength of interactions. Inbirds, it is often assumed that feeding in groups increases foragingefficiency. We assessed how the reduction of seed resources provoked by cattlegrazing affected different properties of seed-eating bird flocks in woodlandswith the same structural characteristics but differing in seed abundance. Underlower availability of grass seeds (i.e. under grazing) flocks were smaller andless rich, and birds showed a lower flocking propensity. This pattern could beexplained by three non-exclusive hypotheses. Food reduction caused by grazing(i) decreases the number of seed-eating birds, and concomitantly generatessmaller flocks; (ii) reduces the density of nuclear species, decreasing thegroup cohesion in large flocks; (iii) makes large flocks less attractive byincreasing individual competence for food. Our results provide evidence thatcattle grazing affect seed-eating birds? interactions, and suggest theimportance of understanding flocking behavior to bring about managementactions.