Thanks! 

Bird Ringing and Banding Schemes (volunteers and professional ornithologists) around the word use a large variety of methods for the safe capture of birds, which depend somewhat on the species or groups of species of interest. There may be a local group who can help you. Often is it is necessary to undergo training and hold permissions prior to catching wild animals. 

Do also consider making use for the large extant collection of birds in Natural History Museums which are particularity valuable for morphological studies due to the large sample size required.

Thanks for your insights and suggestions! 

In terms of sample size, you may want to think about looking at some historical data for the species you're interested in (for example, Birds of North America accounts often have averages +/- SD for various morphological traits), then using these in calculating needed sample sizes - there are good resources here to identify the test you need to use: http://www.biostat.ucsf.edu/sampsize.html

And as for low-impact capture methods, Potter traps are an excellent option for those species suited for it - but you should always check on the methods recommended by whatever ethics organization oversees your work - in Canada, it's the Canadian Council on Animal Care, but elsewhere in the world there are similar bodies that set standards for animal capture and handling. 

For different species you have several methodologies and traps, like mist nets, cages and, of course, it relays on your objectives, in what you really want to do. In some aspects, an observation could also be used as a capture, if you are able to identify each individual (e.g if they have any kind of visual marks)...

It depends on the species of birds. For small songbirds usually 12 and 6 m mist nets are used to capture them. Using playback calls can also help get birds into the net. Also, museums and teaching collections have a large number of samples that would be really useful. Also, keep in mind that handling of any wild species of birds requires permits, for both the state and federal government. https://www.fws.gov/permits/applicationforms/ApplicationLM.html#MBTA

Although this won't be of any direct help to you, I abandoned my training (twice) for a ringer permit after some tragic consequences using mist nets: twice on land, and once over an incoming tide (waders). All these occurences were under the direct supervision of qualified and highly experienced ringers - two were professional operations, one amateur. Personally, I didn't consider the costs worth the benefits.

So, all I'm saying, is be careful!

Hi Jehron Andrei:

the techniques to use will depend on the scope of your work and the objectives you have.  In some cases and for a determined species, some researchers have designed specific traps that take advantage of the behaviors they have. However, if the objective is to use as many species as possible, you will have to use mist nets for sure.  Make sure you have the proper training or at least some experienced people to help you with that.  You will need also de official permits to use them (as in many cases is required).

Good luck in your endeavors.

Fernando Villaseñor

Facultad de Biologíqa, UMSNH

México

Hello Jehron Andrei:

Depending on the size and diet of the birds you can try Balchaptra Tramps. For small birds definitively mist nets. Some people use safely net-guns. Once again depends on the size of birds you want to measure. Like other colleagues mentioned, do not forget to check for any restrictions and permits.

Cheers,

Jafet