recognize a vector of struct as a vector of trait object

Question

There is a trait Animal defined and 2 struct (Cat, Dog) that implement it:

use std::rc::Rc;
trait Animal {
    fn make_sound(&self) -> String;
}

struct Cat;
impl Animal for Cat {
    fn make_sound(&self) -> String {
        "meow".to_string()
    }
}

struct Dog;
impl Animal for Dog {
    fn make_sound(&self) -> String {
        "woof".to_string()
    }
}

Then I define a struct Zoo to accept Animal into a Vec<Rc<dyn Animal>>:

struct Zoo {
    animals: Vec<Rc<dyn Animal>>,
}

impl Default for Zoo {
    fn default() -> Self {
        Self { animals: Vec::new() }
    }
}

impl Zoo {
    pub fn add(&mut self, animal: Rc<dyn Animal>) {
        self.animals.push(animal);
    }

    pub fn add_many(&mut self, animals: Vec<Rc<dyn Animal>>) {
        self.animals = animals;
    }
}

fn main() {
    let dog = Dog;
    let cat = Cat;
    let mut zoo = Zoo::default();
    zoo.add(Rc::new(cat));

    let mut vector = Vec::new();
    vector.push(Rc::new(dog));

    zoo.add_many(vector);
}

Now add(mut self, animal: Rc<dyn Animal>) works as expected, but add_many(mut self, animals: Vec<Rc<dyn Animal>>) complains about

expected trait object dyn Animal, found struct Dog

Why is Vec<Rc<Dog>> not recognized as Vec<Rc<(dyn Animal)>>?