Tough to be entirely sure, but this is probably the Big Brown Bat.
I spent another evening shooting bats with Bill Forbes at his Elephant Head Pond along with a couple of the upcoming bear trip participants Dixie Pearson and Kathleen Reeder. In just one full night I was able to photograph 79 bats drinking. Of course some were going the wrong way. After editing I chose 9 keepers that I was happy with. This is the 4th time I've photographed over Bill's pond and these were the best set I got. I used 2 cameras, the 5 D Mark II with the 500 F4 and the 7D with the 70 - 200 2.8. Almost all of my favorite shots were with the 5 D and larger lens combo. You end up clipping more wings that way but I like the close ups better so it's a fair trade in my opinion. Almost all of the set up is done just before dark. Although I own a phototrap that Bill makes (Phototrap.com) Bill sets up his own equipment which involves multiple trips and 4 to 5 flashes. When the beam is broken it sets of the flashes, The camera is set for F16 and 20 sec exposures so the flash is the trigger, not the camera. The camera just records the image when light is available. You have the choice of triggering the camera yourself when you see a bat, or just leave it consecutively taking pictures as long as you are there. I chose the latter this time which allowed me to take pictures all night long. I left the cameras in Med Raw, and twice I changed the batteries and recharged them in the evening and once changed a cf card. This was easy since I just camped there but Bill has a nice cabin set up for visiting photographers at a very reasonable rate ($60 night). We ended up photographing at least 3 species that June evening, a pallid bat (Antrozous pallidus) which is the blond one above, a big brown bat (Eptesicus fuscus) that is skimming the water and at least one of the many Myotis spp found in Arizona. If you are interested in shooting on the pond please feel free to contact me and we can set up an evening. Or you can contact Bill directly and he can set you up as well.
The endangered long nosed bat approaches an agave flower to insert it's long tongue into the flower to lap up the nectar. They will feed almost all night.
My favorite time to shoot bats there is when the nectiverous bats come in to the hummingbird feeders and agave flowers in late August and September. It's possible to get hundreds of shots in an evening using the phototrap system.
This shot and the one below were taken with a 5 D Mark II and a 17 - 40 mm lens so I had the camera just inches from the flower to get as much detail as possible. There were 5 flashes set up here to make sure I got detail on the bats what ever direction they came from. The species of bat is actually an endangered species known as the Mexican Long Nosed bat (Leptonycterus nivalis). There is another nectar drinking bat, the Mexican long Tongued bat (Choeronycteis mexicana) and with a photo they can be distinguished from each other when they are flying. If you look on the photo below you will note that the membrane on the legs of the one of the species looks like "pants" as it is not continuous as is the other. That is the Mexican Long Nosed, the one with the complete skirt is the Long Tongued bat. Both are migratory species and in the few months they spend in Arizona they change locations to follow the large night flowering plants with whom they have a symbiotic relationship. They are known pollinators of many species including saguaros and Organ Pipe cactus. In Mexico they concentrate on agave and yucca flowers, both of which are used to make spirits such as tequila and mescal. It was originally thought that private tequila "stills" were resulting in reduced food sources but more recent studies dispute this. In fact, some of the large factory tequila mescal farms may actually be benefiting either or both species.
"chomping on some pollen"
They also eat pollen and of course when they go in for nectar their faces are covered with pollen from the flower they just left. This spreads and helps sexually reproducing plants pollinate, hence both species benefit from the relationship. It is quite exciting to see up to 40 bats hovering around one flower stalk. If you are interested I highly encourage you to contact myself of Bill so you can experience and photograph a phenomena in nature few even know about much less see.