Due to the importance of the leptin gene in endocrinology, its existence and behavior in birds have been the focus of considerable debate. The possible inclusion of human contaminant sequences into early bird genome assemblies seems to have been a major complicating factor in understanding Leptin genes in birds. Only recently, with the availability of the Pigeon genome with a well annotated leptin gene has it become evident that birds have a novel gene that has sequence similarity to the mammalian leptin. However, debate regarding its function, tissue specificity and expression patterns are yet to be resolved conclusively.
With the availability of numerous bird genome assemblies, courtesy of the NGS revolution in sequencing it is now possible to visualize and may be even quantify the prevalence of the leptin gene across different bird groups. Without debating the naming of the leptin like gene annotated in the Pigeon, we take it as given for all our analysis. A simple blastX search provides numerous significant hits.
Two of the significant hits are from birds, specifically Taeniopygia guttata leptin-like protein precursor and Melopsittacus undulatus leptin precursor. We also get many hits from reptiles before moving to mammals.