Recently, I went out of town to North Carolina and I wanted to set up a way keep an eye on my birdfeeders while I was gone. I found an easy way to do so with the only cost being a cheap webcam and a computer running Linux. The two programs I used were Dropbox and Motion, but for Windows you can use iSpy.
First, install Motion and Dropbox by following the instructions on their websites. Most package managers have Dropbox, but for Motion you will need to either compile from source or use the install script they provide on their website.
Next, connect a Webcam to your PC, I used a Logitech C270 HD Webcam that I got off the internet for about 20 dollars. There are probably other webcams available for less.
With Dropbox runnning, open the terminal and type "cd ~/Dropbox", or whatever the path to your Dropbox folder is, and hit enter. Then, type "motion" and hit enter. With the default settings it should begin broadcasting a feed that you can view by opening "localhost:8081" in your browser. It will save video files if any movement is detected in front of your camera. If the camera is pointed close enough, it should detect birds but you may need to adjust the sensitivity. Documentation can be found here.
It will save the video files to your Dropbox folder, and as long as Dropbox is running, they will automatically be uploaded to your account which can be viewed anywhere.
For Windows, run iSpy and set the output folder to your Dropbox folder. Then start your camera and select 'Record on detect'.
Here is the best clip I have obtained so far: