albinism, Barn Swallow, barn swallows, cancer, Chernobyl, Chernobyl accident, congenital malformations, crippled birds, deformed toes, genetic danger radiation, genetic defects, germline mutation rate, ionizing radiation, leukemia, loss of fitness, morphological aberrations, mutations, natural selection, nuclear accidents, nuclear energy, nuclear power, radiation, radiation induced deformations, survival of the fittest, tumors, tumors in birds, tumours, tumours in birds, Ukraine
When they speak of “loss of fitness” and “natural selection”, below, these are biological science euphemisms for their inability to survive with the defects. In short, they died. Nuclear energy killed them.
“We found evidence of natural selection against abnormalities in both nestlings and adults. First, a total of 33.5% of 248 nestlings from Chernobyl had abnormalities, while only 17.8% of 841 adults had any abnormalities.”
Møller et. al. 2007
Baby Barn Swallow, Photo Credit Mike’s Birds 
Thus, a large percentage of those with “abnormalities” didn’t reach adulthood or not for long. Deformations which impede the bird’s ability to fly would keep it from escaping predators. Beak deformations can make it difficult to eat.
Barn Swallow with a deformed beak.
Note the large numbers of birds studied: “With over 7700 individuals examined for external abnormalities, this provides the most extensive data-set on abnormalities in animals ever recorded.”
“We can exclude that the effects arose from non-radioactive pollution because all study areas were rural without any exposure to industrial pollution“. Møller et. al. 2007
“Elevated frequency of abnormalities in barn swallows from Chernobyl“, by A. P. Møller, T. A. Mousseau, F. de Lope and N. Saino (2007) CC BY 2.5 (Emphasis our own; original without emphasis may be found online for free).
The original had some embedded links. This abstract was one of them. By one of the same authors, it clarifies some of the points above. Unfortunately, the article must be found at a library or purchased online. It dates from 11 years after the Chernobyl accident.
“Fitness loss and germline mutations in barn swallows breeding in Chernobyl, Ellegren H, Lindgren G, Primmer CR, Møller AP., Nature. 1997 Oct 9;389(6651):593-6.
The severe nuclear accident at Chernobyl in 1986 resulted in the worst reported accidental exposure of radioactive material to free-living organisms. Short-term effects on human populations inhabiting polluted areas include increased incidence of thyroid cancer, infant leukaemia, and congenital malformations in newborns. Two recent studies have reported, although with some controversy, that germline mutation rates were increased in humans and voles living close to Chernobyl, but little is known about the viability of the organisms affected. Here we report an increased frequency of partial albinism, a morphological aberration associated with a loss of fitness, among barn swallows, Hirundo rustica, breeding close to Chernobyl. Heritability estimates indicate that mutations causing albinism were at least partly of germline origin. Furthermore, evidence for an increased germline mutation rate was obtained from segregation analysis at two hypervariable microsatellite loci, indicating that mutation events in barn swallows from Chernobyl were two- to tenfold higher than in birds from control areas in Ukraine and Italy.
 Photo Credit for Baby Swallow at top: Mike’s Birds. Baby Barn Swallow, CC-BY-SA (Mike’s Birds Flickr Acct via Wikipedia) http://commons.wikimedia.org/wiki/File:Baby_Barn_Swallow_(4869085102).jpg https://creativecommons.org/licenses/by-sa/2.0/
 Barn Swallow with deformed beak
“Elevated frequency of abnormalities in barn swallows from Chernobyl”, by A. P. Møller, T. A. Mousseau, F. de Lope and N. Saino (2007), CC-BY-2.5