Why are only four slots available in Level 373?

The fifth slot is visibly chained shut throughout the opening.

Which bird remains last?

The large blue bird's crown and black head outline survive after the left bird and nest clear.

Food Hunt: Pixel Puzzle level guide

hard 14 colors

Use cream, dark teal 3, blue 1, and cream 11 in the four-slot bird collage, then dispatch each green leaf nest after a slot reopens.

If the player asks you to sign in, open the video on YouTube instead.

Fresh-tap cream, dark teal 3, blue 1, and cream 11; wait for the nest edge to expose the green front row.
Fresh-tap green 35, wait, then green 13, yellow 6, and green 42; continue gray 12, magenta 4, frozen cyan 5, orange 22, white 6, cream 16, cyan 3, and cyan 6.
Across the leaves, tap green 29, green 9, green 40, green 20, and green 10 with waits when all four slots fill; then tap magenta 4, orange 10, orange 22, dark teal 17, dark teal 20, gray 12, and gray 20.
Unlock cyan 8, cyan 5, cyan 4, cyan 3, cyan 2, and cyan 1 one at a time; after each frozen nest clears, tap blue 9, blue 15, and blue 32.
After the birds separate, tap blue 23, blue 21, blue 9, red 4, red 6, magenta 4, brown 1, brown 9, gray 3, gray 11, gray 12, orange 11, orange 5, orange 1, white 3, white 4, white 10, yellow 11, yellow 12, yellow 4, pink 10, pink 14, and pink 16.
Fresh-tap black 52 and wait as its active remainder reaches 48, 12, and 10; tap blue 34, blue 28, blue 22, cyan 14, cyan 12, cyan 10, cyan 2, cyan 1, white 24, pink 28, pink 14, pink 10, magenta 1, white 1, cyan 1, cyan 10, and blue 22.

Colors in this level:

Cream, Dark-teal, Blue, Green, Yellow, Gray, Magenta, Cyan, Orange, White, Black, Pink, Red, Brown

Wait for cream to drain before loading the first green wave.
After the green wave, preserve the reopened fourth position for blue 9, then blue 15 and blue 32.
Treat green 35, green 13, and green 42 as fresh exposed nests, not opener remainders.

Board notes 5 details

Layout: A large blue bird overlaps a smaller pink-gray bird, green leaves, an orange-red flower, eggs, and a lower nest; one tray slot is chained shut.
Goal: Clear leaves and nest, separate the two birds, then remove the large bird's blue body and black-edged head.
Opening: Fresh-tap cream, dark teal 3, blue 1, and cream 11 into the four usable slots.
Danger Zone: Frozen cyan nests and large green batches can block blue when only four active slots are available.
Mechanics: The four-slot queue contains frozen cyan tiles; the smaller bird disappears well before the large blue silhouette.

Why are only four slots available in Level 373?
The fifth slot is visibly chained shut throughout the opening.
Which bird remains last?
The large blue bird's crown and black head outline survive after the left bird and nest clear.