Meteor - Using collection on client startup

Why this code shows "0"? Shouldn't it return "1"?

Messages = new Meteor.Collection("messages");

if (Meteor.is_client) {
    Meteor.startup(function () {    
        alert(Messages.find().count());
    });
}

if (Meteor.is_server) {
    Meteor.startup(function () {
        Messages.insert({text: "server says hello"});
    });
}

If I do the "Messages.find().count()" later, it returns 1.