## 3 Problem Scenario  
Before our proposed scheme is discussed, it is important to describe the problem scenario. After that the proposed scheme is presented.  
Most WSN applications generate bursty traffic and the nodes in such applications may not be homogeneous (e.g., multimedia nodes, scalar nodes). For instance, the habitat monitoring and more particularly the wildlife monitoring is one of the realistic applications where nodes may be heterogeneous and high capacity nodes (multimedia/camera) may be deployed close to low capacity nodes (e.g., scalar). The WSN based wildlife monitoring systems have gained significant importance for monitoring and protection of wildlife species. These applications are beneficial in animal detection, animal behavior detection, and environmental observation. In wildlife monitoring systems, several heterogeneous sensor nodes (e.g., scalar and multimedia) are widely deployed for habitat environment observation, such as temperature, humidity, wind, animal movements, etc. [32; 33]. These sensor nodes work collaboratively to monitor the sensor field. In order to analyze the condition of animals (e.g., animals health, food and water conditions, behavioral condition, etc.) in severe environmental conditions, the low resources scalar nodes sense the temperature, humidity, wind conditions while the camera nodes capture the visual information and forward the information towards the base station(s). When the scalar nodes detect the variation in environmental factors, these nodes may inform the available camera nodes in their vicinity to capture the effect and finally transfer the captured data towards the sink or base station. The concerned authorities (e.g., wildlife department) may utilize the gathered data to analyze the effect of environmental condition on wild species and may take necessary measures accordingly.  
These heterogeneous nodes generate various kind of traffic such as audio, video, and scalar as discussed before. In case of event detection, multiple nodes in the vicinity that detect the event may generate a massive amount of data simultaneously and transmit the data toward the CHs. Due to bursty traffic, the CHs may be overloaded as they receive and manage data from all the members of cluster. This may affect the lifetime of CHs. Therefore, minimizing the energy consumption of CHs plays a vital role to prolong the lifetime of the WSNs. In order to enhance the network lifetime, an efficient CH declaration mechanism is of upmost importance.  
In the literature, several approaches have been devoted for efficient CH declaration [16; 17; 18; 19]. These proposed schemes consider residual energy, distance from member nodes, and distance from the sink node as important parameters for a node to be selected as a CH. However, these approaches fall short for the case of high-volume traffic. If the selected CH has high residual energy and short distance from the sink node and member nodes, however, the storage and computational capability (capabilityof a node to execute instructions per unit time) is low, the CH may not accommodate the incoming data received from cluster members effectively. This may result in packet drop and re-transmissions of packets in the network. Similarly, due to low computational capability, the CH may spend more time in data processing, thereby, consumes more energy. Furthermore, the frequency of re-clustering increases which ultimately brings extra control overhead in the network. Therefore, the storage and computational capability of a node are the most stringent factors for optimal CH and to mitigate packet drops and re-transmissions in the network.