You forget that paper is from the mid-80s. I don't understand why people think they just stopped replacing birds. The authors of that paper based it all on declassified documents that were almost 30 years old even then! If anything the government just got better at hiding what they were doing, mark my words in another couple decades it'll come out that it's not only the pigeons and starlings that have been replaced but also robins, seagulls, and a variety songbirds!