Canopy structure drives orangutan habitat selection in disturbed Bornean forests

Abstract

The conservation of charismatic and functionally important large species is becoming increasingly difficult. Anthropogenic pressures continue to squeeze available habitat and force animals into degraded and disturbed areas. Ensuring the long-term survival of these species requires a well-developed understanding of how animals use these new landscapes to inform conservation and habitat restoration efforts. We combined 3 y of highly detailed visual observations of Bornean orangutans with high-resolution airborne remote sensing (Light Detection and Ranging) to understand orangutan movement in disturbed and fragmented forests of Malaysian Borneo. Structural attributes of the upper forest canopy were the dominant determinant of orangutan movement among all age and sex classes, with orangutans more likely to move in directions of increased canopy closure, tall trees, and uniform height, as well as avoiding canopy gaps and moving toward emergent crowns. In contrast, canopy vertical complexity (canopy layering and shape) did not affect movement. Our results suggest that although orangutans do make use of disturbed forest, they select certain canopy attributes within these forests, indicating that not all disturbed or degraded forest is of equal value for the long-term sustainability of orangutan populations. Although the value of disturbed habitats needs to be recognized in conservation plans for wide-ranging, large-bodied species, minimal ecological requirements within these habitats also need to be understood and considered if long-term population viability is to be realized.

Keywords: Bornean orangutan; Carnegie Airborne Observatory; Light Detection and Ranging; conservation; movement ecology.

Fig. 1.

(A) Location of the study site within Sabah, Malaysia. (B) Canopy height within and around the study site, Lot 2 of the LKWS, with an example of a flanged male orangutan movement path used in the analysis. (C) Depiction of an SSF generated along an example movement path (the black line depicts the observed movement, and the gray lines show the available steps the orangutan could have taken). Red blocks in A and B indicate zoomed-in areas in B and C, respectively.

Fig. 2.

(A–G) Box plots of model averaged β coefficients from all individuals and across orangutan age and sex classes derived from individually applied SSFs. The solid line in each box indicates the median for each age and sex class, whereas the top and bottom of the boxes depict the third and first quartiles, respectively. Whiskers denote the maximum and minimum values, or 1.5-fold the interquartile range (whichever is smaller), and dots represent outliers. Values above the solid line at zero (positive coefficients) indicate selection for a given covariate, whereas values below (negative coefficients) indicate selection against a given covariate.