Too many skeleton horse spawns

On my W10 hosted (PE and W10 clients) survival world, after 0.15 a lightning storm resulted in 10-14 skeleton horses appearing around a base of mine. Watching from under cover it appeared they spawned at every lightning strike. Nice loot of arrows, bones and enchanted iron helmets but rather more occurrences than I'd expected. (Easy mode, Birch Forest Biome)