The Hummingbird is a fantastic tour, and a great way to experience the contrasts that South America has to offer. Of course though, travelling across the continent also means you will take in some varying weather conditions during the trip. We're planning to run tours in every month of next year, despite the changing climate - the right departure for you will probably depend on which of the areas you're most keen to see at their best.
Being firmly in the Southern Hemisphere, Rio has the opposite seasons to us here in the UK, the warmest time being November through to March. It will be cooler in the other months of the year although it never really dips below 18°c at any time. The Iguazú Falls have the same seasons as Rio, although the jungle environment makes it feel more tropical, and during their summer it can be very warm and sticky.
Once you get into the Andes and the higher altitudes of Bolivia and Peru, the weather will change significantly. The colder months will still be April through to September, when at night temperatures can drop below freezing. But these lower temperatures also produce the clearest skies, making sightseeing all the more spectacular. Machu Picchu looks its best at this time. The warmer months of November through to March are also the wettest, so this is the downside of the hotter part of the year. Being at altitude however the nights in this part of the world are cold all year and you can expect even in the balmiest months to experience lows of 7°c.
We find that our clients all have favourite times of the year depending on individual preferences, but I would probably say as a compromise that April and May or September and October would be my optimum months for a trip of this nature. Having said that if you are limited to a certain time of the year due to commitments, don't worry. We only run tours when we feel the weather will not hinder the tour, and the places that you visit on the Hummingbird more than make up for any adverse weather. And as long as you bring a mixture of hot and cold weather clothing your enjoyment of this fantastic continent should not be compromised.
One final thing to mention is that next year, for the first time, we are also running trips in reverse! We'll have tours beginning in Lima and ending in Rio, if you fancy some sun-kissed beaches at the end of the tour.