Hummingbirds are only native to the Americas and there are more than 340 species of these tiny birds. Their rapid wing beats give them the ability to hover, fly forwards, fly backwards and even to fly upside down. Different species have beaks of varied length, enabling them to specialise (with their manoeuvrability) on particular tubular flowers with nectaries at their base. Hummingbirds are purely nectivorous. The flowers produce nectar to encourage visits from the hummingbirds, facilitating pollination. We tend to think of the birds exploiting the flowers but one could regard the flowers as 'enslaving' their avian associates by offering a fairly minimalistic bribe (only a few microlitres of weak sugar solution). Some species of hummingbird can be highly territorial (when the benefits outweigh the costs) and will defend areas of flowers from encroachment by conspecifics. Workers at St Andrew's University have found that the Rufous hummingbird visits flowers in a particular sequence (https://www.theguardian.com/environment/2020/jul/08/bright-feathers-bright-brains-hummingbirds-can-order-numerically). Whilst they were not able to establish that these 'birdbrains' could count, they did appear to be able to distinguish between particular flowers. This would fit with the observation that, in order to efficiently forage, these birds must have some concept of 'time since the last visit', enabling them to time returns to a flower, when its nectar has been replenished. I am sure sure that the birds need much of an intellect to do this.
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