That doesn't follow. Birds are generally prey and have a typical prey strategy; they lay lots of eggs and expect few chicks to reach adulthood, while the large

That doesn't follow. Birds are generally prey and have a typical prey strategy; they lay lots of eggs and expect few chicks to reach adulthood, while the large majority become food for someone. Sparrows lay about four eggs per year and become >10 years old, for example. You should expect lots of sparrows to be eaten. Otherwise, the number of sparrows would grow by >100% per year. What this study says is that the number of chicks to reach adulthood is below two per hen, sustained for 50 years.