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Keywords:

  • avian frugivore;
  • hornbill;
  • minimum viable population;
  • parrot;
  • Philippines;
  • pigeon;
  • population estimate;
  • protected area

Abstract

Avian frugivores across Southeast Asia, and in the Philippines in particular, are seriously threatened owing to massive loss of habitat and direct exploitation through hunting and the pet trade. Their declines may have dire consequences for wider ecological processes as many frugivores are also seed dispersers. Twenty-five species of pigeons, parrots and hornbills were surveyed using distance sampling along nearly 500 km of line transects at 14 sites across the island of Luzon. We documented surprisingly few reliable disappearances of frugivores from individual forest patches – in fact ours and other fieldwork since 2000 have increased the known extent of occurrence of several species. However, green racquet-tail Prioniturus luconensis has been recorded at only seven out of 29 historic sites in the last 10 years; although possibly a function of poor coverage, this may be a real range contraction. Still more alarming was the absence of large parrots from most sites with apparently intact habitat surveyed. Even where present, large parrots exhibited lower densities than related species in similar habitat in Southeast Asia. Multiplying site-specific density estimates by reserve area, we estimated population sizes for species in five reserves selected from the current protected area network. For six species, including four of six parrots, largest populations in any reserve in Luzon numbered < 1000 individuals, and nearly one-third of all populations in reserves were < 100. Given differing opinions and evidence on minimum viable population (MVP) thresholds, we used a range of MVP values to predict the likelihood that frugivore populations will persist in various reserves. At MVPs of 500, frugivore communities in all but 2–3 of the largest reserves are not expected to survive. Although seed dispersers may fare better than seed predators (large parrots), and many frugivores are good fliers that can disperse between widely separated sites, we express the concern that without stricter species and site protection a major collapse of frugivore communities may occur across Luzon, with serious implications for ecosystem functioning.