The Tamron and Sigma 160-600mm lenses are popular among "birders". Sigma also makes a 60-600mm. These lenses currently cost between $1000 and $2000. Be aware that they are all relatively large, heavy lenses. The lightest of them is about 4.5 lb. (incl. tripod ring & lens hood). The heaviest is over 6 lb. For anything more than a few moments shooting you will probably want a sturdy tripod or at least a monopod with any of them.
150-600mm and 60-600mm lenses compared (B&H Photo).
If the above lenses seem a bit too much, some others you may wish to consider are a trio of 100-400mm lenses available from Sigma, Tamron and Canon. 400mm is still quite powerful telephoto on a Canon T7 camera and these 100-400mm are all considerably more compact and lighter weight than the above lenses, ranging between roughly 2.5 lb and 3.5 lb. The Sigma and Tamron are also a bit more affordable at $799. Between those two, the Tamron can optionally be fitted with a tripod mounting ring (sold separately for $129). There is no option to fit a tripod ring on the Sigma. The Canon is the largest and heaviest of these three and comes with a tripod mounting ring. It is easily the most premium of all the lenses listed here, with the best image quality, best build quality/durability, better sealing for dust and weather resistance and best general performance. The Canon EF 100-400mm II is also the most expensive at $2199 (on sale currently, regularly $2399).
100-400mm lenses compared (B&H Photo)
There also is an earlier version of the Canon 100-400mm lens that's quite capable, slightly lighter weight and might be found in reasonably good condition used for under $1000 (MPB.com);
There also were earlier versions of Sigma and Tamron zooms with 150-600mm, 150-500mm and 120-400mm focal lengths that might be found used. Honestly I hesitate to recommend any of them at this point, as they don't have as good image quality, functionality and features as any of the above lenses.
You can find much more detailed reviews about, sample images done with, and sharpness and other testing of most of these lenses at Bryan Carnathan's website.
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Alan Myers
San Jose, Calif., USA
"Walk softly and carry a big lens."
GEAR: 5DII, 7DII (x2), 7D(x2), EOS M5, some other cameras, various lenses & accessories
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