Hogwarts grounds

So saying, he stood, dusting off his trousers and adjusting his open robe. Harry and the others quickly copied him.

They began to walk around the shore, with Apa keeping pace in the water beside them. As they walked, Slytherin and Apa explained more about the relocation of both the squid and the merfolk clans. Slytherin, it appeared, was an expert on magical creatures and beings, and he could speak many of their languages. He had taken the small lake on the grounds and expanded it, in part to create more impenetrable defenses on the far side of the valley, and in part to make it more hospitable for larger creatures.

He had worked to build up the ecosystem of smaller fish in order to sustain the larger creatures, and finally had searched the world for candidates who wanted to migrate. He had even imported grindelows and a small herd of hippocampus, both of whom were raised and kept in check by the merfolk clan.

In return for living in the lake and being within the safety of the Hogwarts wards, both the squids and merfolk helped teach the students and formed a part of the school's defensive force. They patrolled the edges of the lake regularly, looking for attackers on the far shore and students in danger or misbehaving on the near shore.

They also gathered plants that grew underwater for Hufflepuff, Apa explained, though Slytherin said that she would teach the trio more about that herself.

By the time they had gotten to the farthest shore, where the lake met the forest, the children were exhausted. Apa bid them farewell and slipped back into the water's depths, while Slytherin just fondly complained about their stamina. He cast a spell with his hand, though none of them could tell what it did, and then instructed them in reversing their earlier spell. By the time all three had succeeded in vanishing the water-bubble shields over their ears, a new creature had appeared.

Harry thought these creatures were less friendly-looking than Apa had been, but somewhat more impressive. They were like horses, but with large black, leathery bat wings. Their manes were stringy and their coats pure black. "What are they?" he asked Slytherin.

"What are what?" Hermione asked innocently.

Slytherin nodded at Neville. "Can you see them?" Neville shook his head quickly. "Congratulations to you both, then." He turned to Harry. "The creature you see is called a Thestral." Neville twitched. "They are very gentle and obedient creatures, and they do much for us around the castle and village."

"However, as with many things in magic, there is a price for their help. Only certain people can see the Thestrals; only those who have witnessed the death of another. For those who have not experienced that horror, the Thestrals will pass them by, and they will never know what they have missed. But for those unfortunate enough to be able to see them, the Thestrals will provide wonderful assistance."

"Who did you see die, Harry?" Hermione asked quietly.

"I- I don't know." Harry admitted. "I guess my parents? They died when I was a baby."

Slytherin nodded solemnly. "That could be it. The mind remembers many things from a young age, even if we are not aware enough to recall those memories."

"So there are Thestrals all around us now?" Neville asked, a little fearful despite Slytherin's reassurances that they were calm and helpful.

Slytherin nodded at Harry to answer. "There are only three of them here," he said, pointing them out. "One a little behind Hermione, sort of diagonally. And there are two beside Slytherin, one on each side. I think he has treats for them in his pocket, because the one keeps nudging his hip."

Slytherin laughed and pulled a handful of meat scraps from his open robe's inner pocket. "Spot on, young Harry!" The three Thestrals immediately made for the treat, the farthest one pushing past Hermione to get to it.

"Oh!" she exclaimed. "I felt that!"

"You can feel them even if you cannot see them," Slytherin confirmed. "Now, have any of you ridden a horse before?" he asked.

All three shook their heads, causing Slytherin to sigh. "It will take much time before you are ready to see the outer wards and defenses. For today, we will simply circle back around the lake."

It took him the better part of half an hour to get the trio onto their Thestrals, hampered by the fact that Hermione and Neville couldn't see what they were supposed to be grabbing onto. Fortunately, the Thestrals were indeed quite docile, and Harry's tolerated him with good grace while they watched the other two struggle onto their mounts.

Eventually, all three children were mounted, and the quartet continued through the trees along the lake shore. As they rode, Slytherin walked beside the Thestrals, telling the students about some of the creatures and animals he had brought to Hogwarts.

The smallest magical creatures were snakes and birds, both of which, Slytherin explained, he had an affinity for. He had recruited a number of magical birds, including augureys, jobberknolls, thunderbirds, golden snidgets, phoenixes, owls, hoopoes, boobries, and diricawls.

Of course, having just learned about the magical world, Harry had no idea what any of those birds were, save for the owl, which made him miss Hedwig. Hermione, having read some magical texts before coming to Hogwarts, and Neville, having grown up in the wizarding world, were more familiar with the names, if not the actual abilities of the birds.

As Slytherin explained, augureys, thunderbirds, phoenixes, and diricawls had the ability to disappear from one location and appear in another. Each one traveled in a different manner, but the effects were the same. Thunderbirds were incredibly active in stormy weather, while augureys preferred fog and light rain. Phoenixes, on the other hand, preferred sunny days. Between the three, one was nearly always active and at its best, regardless of the weather. The Diricawls were flightless, and thus had a different perspective than the others.

The other kinds of birds could not transport magically, though the snidget was too fast to have anything but magical augmentation. However, they had their own advantages on Slytherin's sentry squad. The snidgets could fly incredibly fast, the boobries could swim almost as quickly and created illusions so that they appeared to be different animals. Hoopoes had a distinctive warning cry, but also ate pests that would hurt the forest. The owls had amazing eyesight and were active at night, and the jobberknolls were absolutely silent, capable of great stealth.

Slytherin could communicate with all of those magical birds, through a chirping language that he called volucris lexis, the language of winged creatures. He could not communicate with non-magical birds, but the magical birds could, and acted as relays and translators.

The non-magical birds in the area were mostly native, though Slytherin had imported more crows, ravens, herons, robins, starlings, and mockingbirds. All were extremely intelligent, and unlike other intelligent birds such as parrots, these species were able to survive and thrive in the harsh Scottish environment.

Slytherin also pointed out the birds he had brought who were not a part of the school's security. Chickens, ducks, and geese were raised for meat in the village, while game turkeys, partridges, and pheasants roamed the forest. Farmers' friends, such as swallows and hummingbirds, were transplanted near the gardens and greenhouses.