It looks like it was quite an overcast day (cloudy) as far as lighting went - this has meant that you get nice soft light and subjects like the tigers and birds are not showing bright glaring overexposed hotspots on their fur - however its also meant that you've had to up your ISO often to 800 to get a fast enough shutter speed - whilst also having your aperture wide open (f5.6 for a variable zoom at the long end which I what I assume you were using) which has left you with less depth to work with in each shot.
My first feeling though is that quite a few shots have a colour haze over them - I would attribute this to probably shooting through glass or general shooting. If you ever approach RAW processing and shooting adjusting the white balance yourself can help overcome this problem (unless you get a really god evening/morning sunny cast that you want to keep of course).
At it stands your best friend is going to be levels in editing. Even using a basic editing package you should have a levels tool option and using this you can lose the haze. You will have to open up the levels tool and then there should be 3 eyedrop tools somewhere on it - select the blacks dropper (often the one on the far left) and click a spot in teh shot that is supposed to be pure black. This might also darken the shot a bit.
I used this on the following two of your shots to get:
I also used a method called highpass sharpening to add some "punch" and contrast to both images.
In photoshop elements (or any editor that has an unsharpen mask) its the following:
Enhance (from the top bar menu) - Unsharpen mask
With the settings:
Amount : set to a level that you like based on its effect on the shot (this is the last setting you set and is really down to personal preference - I used low values of around 18ish for both these shots)
Radius - 250
Threshold - 4
I would also add the following two stages to the fullsized versions that you have (and that I didn't do to the above shots)
A noise reduction move:
Filters - noise - reduce noise
Strength 10
Preserve details 95%
Reduce Colour noise 24%
And finish with a regular sharpening (again on the fullsized images)
Unsharpen mask with the following settings
Amount - again you choose though do go higher to around 100% or greater = but keep an eye on the 100% crop view to make sure its not getting noisy/grainy
Radius - 0.8
Threshold - 4
Resize and then sharpen with the unsharpen mask again before uploading to the net (note you will end up using a smaller and different amount as you will need far less sharpening for this stage)
Note the above is a common set of values and processes that I follow and better understanding and use of each tool can deliver better results - this is a good starting point however.