Extreme Temperatures
The birds, swifts specifically, often make their nests in buildings where construction materials such as concrete or sheet metal are used. These conditions, combined with an ongoing Spanish heat wave that has seen temperatures soar to over 104 degrees Fahrenheit in recent days, can turn their nests into ovens.
"They're literally being cooked," said Elena Moreno Portillo, an animal activist at the Seville-based conservation group Ecourbe told The Guardian newspaper.
The group's Facebook page shows how people have been collecting boxes full of the baby birds. In Seville and Cordoba, where there are large urban colonies of swifts, as many as 100 have been collected in a single day.

The Rainbow Ski Area team has been working “non-stop” to get the mountain ready for the season, with plans to open two weeks early.
Rainbow Ski Area mountain manager Thomas Harry said the snow over the past week could set them up for the season.
"It's extraordinary for this time of year ... We are stoked."
The team was now aiming to open next Friday for the Matariki public holiday - two weeks earlier than expected.
A gas shortage and high prices will send "shockwaves through the country," leading to landlords cutting the heat for tenants and widespread company bankruptcies, warned Klaus Müller, the head of Germany's Federal Network Agency, which is the regulatory office for electricity, gas, telecommunications, postal services, and railway markets.
Müller paints a bleak picture about the crisis in an interview with German newspaper Rheinische Post, saying it will "send shockwaves throughout the country. Banks will ramp up their business with installment loans, and ailing companies will fall into insolvency."
Müller's office, which is a federal agency within the Federal Ministry for Economic Affairs and Climate Action, has a bird's eye view of the economic situation in Germany and also special insight into how economic conditions will develop into the future.
Müller says he expects gas prices to continue to climb, resulting in increased inflation that goes far beyond energy. He also warns that there will be a dramatic lack of gas in the winter, which could lead to landlords turning down the heat to save on energy. In turn, Germans may have to grapple with colder apartments.
While the warning won't impact the Lower Mainland or the surrounding area, if you're travelling east by car you may want to proceed with caution.
Fifteen to 20 cm of wet snow is expected to fall on Highway 3 between Paulson Summit and Kootenay Pass. Parts of Elk Valley could see up to 10 cm.
Environment Canada calls the June precipitation "unseasonable snowfall."
The Juneuary snow is thanks to a low-pressure system over Alberta that is bringing prolonged rainfall to the region. Parts of Alberta face a state of emergency due to the same weather system.

The province announced that Highway 40bwill remain closed between Kananaskis Lakes Trail and Highway House/Highway 541 due to avalanche hazard, and will remain closed Wednesday.
Peter Lougheed Provincial Park got hit hard over the last few days as cooler temperatures turned a forecast of big rain into a late spring snowstorm.
As a result, campgrounds and trail heads that would normally be jammed with hikers at this time of the year are deserted.
And as you head north along the Smith Dorrien Trail, wet heavy snow makes it difficult to drive.
Castle Mountain Resort employees woke up to find more than half the mountain covered in a layer of powder.
"Being in the Rockies, anytime of year, you'll for sure see dustings of snow up on the alpine," said guest services coordinator Kelly Dolan.
"But to wake up to close to 30 centimetres at mid-mountain, the snow line's even a little bit lower than that, is unexpected for sure."
Whitefish Mountain Resort has announced they are closed Tuesday and all activities have been canceled because of wind and snow.
The resort will be providing updates at https://www.facebook.com/skiwhitefish.

A construction worker drinks water to fight the scorching heat during a heatwave in Seville on June 13, 2022.
He told AFP that the current heatwave would bring "extreme temperatures" and "could last until the end of the week".
The mercury will rise above 40 degrees Celsius (around 104 degrees Fahrenheit) in the day in many Spanish towns and remain high at night, above 20 to 22 degrees, he said.
According to Spain's national weather agency, the earliest heatwave on record was recorded on June 11th 1981, making the current episode of soporific heat the second earliest heatwave on record in Spain as it began on Sunday June 12th 2022.
Eight people were rescued in a blizzard on a Tasmanian mountain authorities said, as extreme weather wreaked havoc across the state.
Authorities said two of the walkers, a 27-year-old woman and a 16-year-old girl, were 'very lucky to be alive' and are currently being treated in hospital for hypothermia.
The cold front is travelling north up the Australian mainland, causing large swells along the coast
Comment: Spain in grip of second earliest heatwave on record