Apparatus, systems and methods may be used to monitor data flows and to select and track particularly large data flows. A method of tracking data flows and identifying large-data (“elephant”) flows comprises extracting fields from a packet of data to construct a flow key, computing a hash value on the flow key to provide a hashed flow signature, entering and/or comparing the hashed flow signature with entries in a flow hash table. Each hash table entry includes a byte count for a respective flow. When the byte count for a flow exceeds a threshold value, the flow is added to a large-data flow (“elephant”) table and the flow is then tracked in the large-data flow table.