Is listening to a Dharma talk while walking considered a form of walking meditation? Sometimes when I take a break from work and walk through a nature path, I listen to a podcast called Zencast which is a collection of hundreds of Dharma talks by dozens of teachers over the decades such as Thich Nhat Hanh and Gil Fronsdal spanning a wide array of topics, such as Five Hindrances, mindfulness, meditation, etc. I highly recommend it, it's a great way to consume teachings on an iPod. When I do this, I am present with body in nature and with mind in enlightened knowledge, but is this technically a technique for a walking meditation?
Yes, in walking meditation we can use any of the 40 objects of meditation. 

Listening to Dhamma talks would put it under recollection of the dhamma  as it gave you a sense of appreciation of the truth of the dhamma, IMHO,rather than the investigation of Dhamma (Dhammavicaya).


  "Mahanama, you should develop this recollection of the Dhamma while you are walking, while you are standing, while you are sitting, while you are lying down, while you are busy at work, while you are resting in your home crowded with children.