I have been spending time during the month of February in Cancun and the Riviera Maya since 2007. I can be of some help and I'm always looking to bird with folks while there. For those looking to go out on their own, I have this to say: 1. When renting a car be aware that you WILL pay for extra insurance that you might not be expecting, it's mandatory. Don't try to arrange for it before you arrive from a third party because the companies will insist that you buy it from them. Insurance through your credit card company might cover any deductibles but will not cover your insurance. Plan on $20-$30 per day depending on car category. I have started booking through companies that include the insurance with the rental up front so there are no surprises. This year I'm using America Car Rental because it's been highly recommended to me. <www.america-carrental.com/> I'll post about the experience after this year but I'm tired of the games at the other locations.
Birding is easy and can be done almost anywhere. If you plan on taking camera gear, a tripod or flash will get you labeled as a professional and you either have to pay a fortune (~$500 USD) for a permit at the ruins or not take it in. Know this ahead of time. I had no problem with my Canon 100-400 mm lens on my shoulder but the other items were the problem. I managed to get the flash through once but not the tripod. For that reason I visit the ruins without my gear. I don't take it because I don't leave anything of value in my car. Never had a problem with a break-in but have heard the stories and if there's nothing to steal because I didn't leave it there, I don't sweat it.
The areas nearby the ruins can be very good for birding. As pointed out, the walk from the parking area to the gate at Tulum can be very productive. Yucatan Vireo, Yucatan Jay and Orange Oriole were easy for me along this trail, although the orioles tend to wander widely. The area around Coba is great! Birding inside is OK but I've had everything that I've had inside the ruins in the areas outside and a whole lot more. Warning - I've had my worst experience with chiggers EVER from the area around the lake while there last year, and a good friend that was there inside 2 weeks later had the same experience. The chiggers here must be radioactive because they left welts 5 times normal! LOL Seriously though, take precautions because they were horrible. The areas around town and the lake hold many of the species that you're seeking.
I've not done Ek Balam on my own but I suspect this area is also very productive and the scrub habitats between there Rio Lagartos will give opportunities for species that you'll not have elsewhere on the eastern side of the peninsula. Because the grounds at Ek Balam are more densely forested there were plenty of chances to see birds but being with a guided group you have to keep up. As for Chichen Itza, they day that I was there the grounds were nearly birdless. We drove out in our rental and arrived early, we hired a guide at the gate and did the tour. Afterwards, we had the luxury of walking the grounds and it was very unproductive. We were leaving as the first buses had arrived. I don't remember the surrounding areas being very interesting looking.
Away from the ruins, I visited Punta Laguna for the first time last year. This fresh water lake system is about a dozen miles north of the traffic circle before you reach Coba or about the same from Nuevo Durango from the north. This later town is a long, slow drive from the Cancun area so I don't recommend it. Punta Laguna has great habitat and a greater variety of species. I arrived at noon one day and went back the next it was so good. These 2 lists will give you an idea of what I had and what can be expected. The first was for the area around the parking lot, the second from inside. There was a fruiting tree next to the parking lot that was incredibly active at daybreak, so I spent more than an hour milking that for all that it was worth.
<http://ebird.org/ebird/view/checklist?subID=S17398005>
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Not only were the birds good, the Spider Monkeys in the trees overhead made it better still. I list this as a must go site.
As someone else pointed out, the golf courses can be extremely productive. The par 3 course in front of the Grand Oasis Resort in the center of the Zona Hotelera in Cancun usually has ducks and a few shorebird species. It is the easiest place to find Northern Jacana that I know of. I've never not seen them around the small ponds here and last year there were juveniles as well. I have also seen Bare-throated Tiger Heron here a few times. The Iberostar course a little south of here usually has a larger assortment of shorebirds, though usually nothing unusual if you're from the states, due to its larger water features and its proximity to the lagoon. The golf course at the Grand Mayan in the Riviera Maya hasn't been as productive as I would expect but is still has birds of interest and they can be observed from the roadways and walkways nearby.
The last area that should be recommended is the road from the south end of Puerto Morelos to Leona Vicario, otherwise often referred to as the Ruta de los Cenotes. An early drive along this road almost always yields a Roadside Hawk or two, and Gray Hawks are fairly common. There are numerous places to pull off and bird along this road west out of Puerto Morelos. Make sure that you pull off the road and not try to stop along it. This is a very busy roadway and the shoulders are non-existent along much of it. Trying to bird along it in the wrong spot might get you killed, for no reason other than you getting struck by a passing vehicle. However, there are side roads, especially from about 10 miles west of P.M., that allow you to get off the main road and bird along them and these can be very productive. The locals in the small town of Central Vallarta at about 10 miles +/- (don't blink or you'll miss it) were friendly, curious and helpful. Don't expect any English from them. The habitat isn't as good as at Punta Laguna above, thus the diversity suffers a little but I've had species along this road that I haven't had elsewhere. Plus, this area is close to Puerto Morelos, not far from Cancun, and for those looking to get a taste of Yucatan birding without going too far or feeling too intimidated I think it's a great place to start.
Any questions? Fire away. If you plan to be in the region in early February, drop me a line.