“The factors why these species number are getting lower”
It has been explained in the recently papers that the most essential factor of insectivorous birds decline is mainly food scarcity as the impact of the forest fragmentation. However, the newest study (referenced paper) in La Cruces tropical forest, Costa Rica provides different proofs. The limited dispersal as well as sedentary behavior are found as the main cause of the drop number of insectivorous birds in particular forest fragment.
Why Insectivorous birds are important?
Insectivorous birds are acknowledged as the species which feed primarily of insects and invertebrates. In tropical forest area, their existence is important for controlling the insects that might be harmful when the number is high. Hence, the “control” function lead to the ecosystem and its component in balance condition. Unfortunately, due to tree-clearance by human disturbances in forest area, their number is getting lower and lower.
Some initial hypotheses have been often discussed as the factors such as food scarcity, microclimate change, habitat specificity, and limited dispersal. Based on those hypotheses, the newest study emphasizes on the bird number, diet types, and invertebrate abundance. Surprisingly, this study states that there are no significantly differences in bird number, invertebrate abundance, and the bird diet in both forest and fragmented area. So, the three first hypotheses are rejected.
Nevertheless, several evidences could not be ignored. The appearances of some specific species of birds in fragmented forest are lower than in forest area such as white-breasted wood wren (Henicorchina leucosticte) and white- throated spadebill (Platyrinchus mystaceus). Even some of the largest and specialized insectivorous birds could not be found in fragment forest anymore such as black-faced anttrush (Forminarius analis) and ruddy wood creeper (Dendrocincla homochroa). In brief, the limited dispersal can be accepted as the important factor of the disappearance of understory insectivorous as they have sedentary behavior.
We should care by taking some ACTIONS!
Furthermore, there are some points that can be considered as the actions to minimize the impact of forest fragmentation to the particular insectivorous bird population. A good integrated program of both human activities as well as conservation strategies should be carried out. For instance “Corridor channel” system that can be linked between fragmented forests. Corridor can be varied in any forms such as fence rows, coffee plantation, and native trees species plantation along the corridor. Thus, the movement of the birds can be dispersed by access another fragment through corridor.
[Paper reference: CaganH. Sekercioglu,Paul R. Ehrlich,Gretchen C. Dail, Deniz Aygen,David Goehring, and Randi F. Sandi. (2002). “Dissappearance of insectivorous birds from tropical forest fragment”. Proceedings of the National Academy of Sciences of the United States of America. Vol 99, No. 1. Pp. 263-267]
