For a supposed UNNATURAL ACT there seems to be alot normality in it.
African Elephant[16]
Brown Bear[17]
Brown Rat[18]
Buffalo[19]
African Lion
Caribou[20]
Cat (domestic)[21]
Cheetah[22]
Common Dolphin[23]
Orca
Common Marmoset[24]
Common Raccoon[25]
Dog (domestic)[26]
European Bison[27]
Human
Prea[28

Chicken (Domestic)[29]
Common Gull[30]
Emu[31]
King Penguin[32
Amazon molly[34]
Blackstripe topminnow[35]
Bluegill Sunfish[35]
Char[33]
Grayling[33]
European Bitterling[36]
Green swordtail[36]
Guiana leaffish[37]
Houting Whitefish[33]
Jewel Fish[38]
Least Darter (Microperca punctulata)[36]
Mouthbreeding Fish sp.[35]
Salmon spp.[39]
Southern platyfish[36]
Ten-spined stickleback[36]
Three-spined stickleback[36

Anole sp.[40]
Bearded Dragon[41]
Broad-headed Skink[36]
Checkered Whiptail Lizard[41]
Chihuahuan Spotted Whiptail Lizard[41]
Common Ameiva[41]
Common Garter Snake[36]
Cuban Green Anole[40]
Desert Grassland Whiptail Lizard[41]
Desert Tortoise[42]
Fence Lizard[41]
Five-lined Skink[36]
Gopher (Pine) Snake[35]
Green Anole[40]
Inagua Curlytail Lizard[41]
Jamaican Giant Anole[40]
Laredo Striped Whiptail Lizard[41]
Largehead Anole[40]
Mourning Gecko[43]
Plateau Striped Whiptail Lizard[41]
Red Diamond Rattlesnake[36]
Red-tailed Skink[36]
Side-blotched Lizard[41]
Speckled Rattlesnake[36]
Water Moccasin[36]
Western rattlesnake (Crotalus viridis)[36]
Western Banded Gecko[43]
Whiptail Lizard spp.[41]
Wood Turtle[40
Appalachian Woodland Salamander[44]
Black-spotted Frog[45]
Mountain Dusky Salamander[44]
Tengger Desert Toad[40

Acanthocephalan Worms[46]
Alfalfa Weevil[47]
Australian Parasitic Wasp sp.[47]
Bean weevil sp.[47]
Bedbug and other Bug spp.[48][49]
Blister Beetle spp.[50]
Blood-flukes (Schistosoma)[51]
Blowfly[50]
Box Crab[52]
Broadwinged Damselfly sp.[53]
Cabbage (Small) White (Butterfly)[54]
Checkerspot Butterfly[54]
Clubtail Dragonfly spp.[55]
Cockroach spp.[56]
Common Skimmer Dragonfly spp.[55]
Creeping Water Bug sp.[57]
Cutworm[58]
Digger Bee[59]
Dragonfly spp.[55]
Eastern Giant Ichneumon (wasp)[47]
Eucalyptus Longhorned Borer[57]
Field cricket sp.[60]
Flour beetle[61]
Fruit Fly spp.[62]
Glasswing Butterfly[54]
Grape Berry Moth[63]
Grape Borer[57]
Green Lacewing[64]
Harvest Spider sp.[65]
Hawaiian Orb-Weaver (spider)[65]
Hen Flea[64]
House Fly[66]
Ichneumon wasp sp.[47]
Incirrate Octopus spp.[52]
Japanese Scarab Beetle[67]
Jumping spider sp.[65]
Larch Bud Moth[63]
Large Milkweed Bug[49]
Large White (Pieris brassicae)[49]
Long-legged Fly spp.[68]
Mazarine Blue[49]
Mediterranean Fruit Fly[62]
Mexican White[49]
Midge sp.[68]
Migratory locust[69]
Mite sp.[68]
Monarch Butterfly[54]
Narrow-winged Damselfly spp.[53]
Parsnip Leaf Miner[68]
Pomace fly[68]
Queen Butterfly[54]
Red Ant sp.[68]
Red Flour Beetle[49]
Reindeer Warble Fly (Hypoderma tarandi)[68]
Rose Chafer[68]
Rove Beetle spp.
A list of some of the animals that regularly have GAY sex.