Orangutan behavior in Kutai National Park after drought and fire damage: Adjustments to short‐ and long‐term natural forest regeneration

Abstract

This study aimed to develop a long-term picture of orangutan (Pongo pygmaeus morio) behavioral adjustments to damaged masting forest around Mentoko, Kutai National Park, Indonesia. Mentoko is regenerating from two severe burnings and is one of few areas where orangutans were well-studied before and early after damage. We studied orangutans' feeding ecology, diet, and activity budgets 12-15 years after the second burning then compared our findings with earlier pre- and post-damage ones to assess the changes and factors involved. By our study, we predicted (1) improved feeding ecology compared to early in regeneration, (2) behavior diverging from the normal foraging strategy and (3) behavior shifting toward pre-damage patterns with improving feeding ecology. Data were behavioral observations on 42 orangutans (422 full day follows, 3,522 hr) and tree plot measures of feeding ecology. Findings were consistent with the first and third predictions but not the second: (1) feeding ecology had improved (plant food abundance was near per-damage levels, but species composition had changed); (2) foraging strategies showed no divergence from normal (fallback-preferred food switches in diet and activity budget adjustments were both normal, notably travel did not reduce), (3) diet and activity budgets had reverted to near pre-damage values by our study. Differently than post-damage studies on other orangutans but consistent with those on other primates, our comparisons showed behavioral adjustments were flexible, multiple vs. single, and influenced by multiple factors. Factors likely involved at Mentoko include type and spatial configuration of damage, duration of regeneration, and P. p. morio's recognized resilience. Findings have value for orangutan and nature conservation in showing that recovery to near-normal levels from severe habitat damage is possible within ca 15 years and in adding to understanding of the factors and processes that contribute to recovery.

Grouping behavior of Sumatran orangutans (Pongo abelii) and Tapanuli orangutans (Pongo tapanuliensis) living in forest with low fruit abundance

“…While logging does not result in low orangutan densities per se (Borneo: Marshall et al, 2006; Seaman et al, 2019; Sumatra: Knop et al, 2004), behavioral changes that accompany logging suggest increased energetic costs (Hardus et al, 2012; Rao & van Schaik, 1997) or decreased nutrient intake (e.g., increased reliance on fallback foods: Russon, Kuncoro, & Ferisa, 2015) in logged or damaged forest. These behavioral changes may ultimately also influence costly activities, such as party formation.…”

Primate social behavior

“…Small, isolated populations are unlikely to possess the genetic variation upon which natural selection works; therefore, we are now looking increasingly at learning and innovative, novel behavior patterns as the sources for adaptions during individual lifetimes, and the cross generational transmission of these behaviors (instead of genetics) for their persistence over time. Examples of these may include the significant increases in terrestrial behavior that have been documented in some populations of muriquis (Tabacow et al, ) and orangutans (Ashbury et al, ; Russon et al, ), but whether they reflect adaptive responses to ecological or demographic stimuli remains to be seen. We can look to the next set of comparative studies of primate (and animal) innovations and traditions for a new generation of insights.…”

What does variation in primate behavior mean?

“…In contrast to behavioral variation, behavioral flexibility always involves a response to external stimuli, and therefore always has a temporal component. The temporal scale can vary from hours or days, such as occurs during fission–fusion events (e.g.,Aureli et al, ), to months or years, as occurs in the adjustments of diets, activity budgets, ranging, and social patterns in response to food shortages caused by seasonality or by natural disturbances such as hurricanes (e.g., black howler monkeys: Pavelka, Brusselers, Nowak, & Behie, ; Pavelka, McGoogan, & Steffens, and spider monkeys: Schaffner, Rebecchini, Ramos‐Fernandez, Vick, & Aureli, ), or by anthropogenic activities that permit comparisons of behavior before and after, or during the periods over which habitats and population densities were altered (e.g., muriquis: Strier & Mendes, ; red colobus: Gogarten et al, ; Milich, Stumpf, Chambers, & Chapman, ; orangutans: Russon, Kuncoro, & Ferisa, ; and other examples in Strier, ).…”