Target birds are those that are special in some way to the traveling birder; their “must see” bird or birds for the trip. There are a variety of personal reasons a bird may be on one’s target list, indeed someone wrote a book listing the top 100 birds (in their opinion) on the planet. Similarly, there are several forum discussions of which birds are the most amazing, colorful, unusual, rare, exotic, or what have you. Typically, these specific few species determine the primary trip destination and at least one or more site locations. For example, if you want to see a White-necked Picathartes, you will need to go to one of the few countries in West Africa that have it, and to one of the few sites within the country where they can be seen with reliability. Hence, the framework for your trip is set.
Few of us will limit our target list to just those few “must see” species and will also want to see the birds endemic to the area. Endemics are bird species, subspecies, or even races of a species with restricted distributions. They may be found only in a particular habitat, area, or country. Regardless, endemics are seen nowhere else on the planet, so if you are in the neighborhood, it’s going to be your only opportunity to see them. You can usually find a list of endemics by country in the text or on range maps of your bird book. Also, trip reports and bird lists will sometimes highlight them. If you are a “lister” (interested in seeing numbers of different species), you’ll probably tailor your trip to add these species.
Target birds may also include birds that although broadly distributed, remain difficult to see due to habitat loss or their own behavior. Often a particular birding lodge or park will have a few “special” birds from these groups. Reading trip reports and tour itineraries you’ll know which birds these are and you won’t be cursing later when asked if you saw the resident Eagle owl that lived behind the pub, now 2000 km away. Of course looking at regional bird club web pages can be enlightening, and forums can produce a wealth of information. Also, don’t neglect the lodge staff upon arrival, they usually have the most recent and accurate information regarding local wildlife.
However you define your target list is entirely up to you. I met a man whose goal was to see all the parrots of the world, and another who wanted to see one bird of every family of in the world. To the chagrin of my birding friends, I tend to gravitate toward birds subjectively described as “cute.” I then tailor my itinerary and study habits to include these species.