Combining multiple API calls into one request

Combining multiple API calls into one request

I'm making a web app called "Your Life in Music" where the user plugs in
his/her birthdate and the app displays the top billboard hit from each
birthday since they were born. The app talks to the Last.fm api to
retrieve the album art for each song. Currently it takes a while for the
app to compile all the album art and someone suggested speeding things up
by combining all the API calls into a single request. I'm a bit of a
newbie though, and I'm not sure this can be done. So my question: How does
one combine multiple calls into a single request?
Here's the app: http://www.dailyspiro.com
And the critical code:
function compileDisplay(birthDays) {
// create an HTML list that for each birthday displays top song, artist,
and album art
htmlObj = {}
for (i = 0; i < birthDays.length; i++) {
var age = birthDays[i][0]; // age isn't equal to i if user was born
before 1958
var date = birthDays[i][1];
var track = billboard[date]['song'];
var artist = billboard[date]['artist'];
getAlbumArt(age, track, artist, birthDays);
}
}
function getAlbumArt(age, track, artist, birthDays) {
$.getJSON("http://ws.audioscrobbler.com/2.0/?method=track.getInfo&api_key=(myApiKey)&artist="
+ artist + "&track=" + track + "&format=json&callback=?", function (data)
{
try {
var image = data.track.album.image[2]['#text'];
if (image ==
'http://cdn.last.fm/flatness/catalogue/noimage/2/default_album_medium.png')
{
throw 'generic image';
}
} catch (err) {
var image = 'images/' + track + '.jpg';
}
compileHtml(age, track, artist, image, birthDays)
})
}