Playing With Petrels Part II: Modeling Climate Change

Yesterday I re-visited the Shire with Sarah and Liam, who has joined the Storm Petrel team. As I have mentioned in a previous post,  they are simulating the 2 degree rise in global temperatures that is projected to occur in the next 50 years, and studying its effects on the Leach’s Storm Petrel population. To increase the temperature in the Petrel burrow, Liam and Sarah have put tiny heaters, wired to a solar panel, into ten of them. There are also ten “sham” heaters that don’t change the temperature in the control burrows.

A heated Petrel burrow, identified by a blue tag, with wiring that attaches to a solar panel

A heated Petrel burrow, identified by a blue tag, with wiring that attaches to a solar panel

The Petrel team has three working hypothesis about the effects of rising air temperatures on the Petrels’ life histories. The first is that the birds, which share parental responsibilities, will spend less time incubating their egg because the burrow will be warmer. Though they seem fragile, Petrel eggs can be left alone for ten days while their parents forage for food, much longer than most bird eggs, which die after a few hours of exposure to the cold. The second hypothesis is the reverse: the Petrels will spend longer in the burrow because they burn less energy when it is warmer, therefore they won’t have to leave for food as often.

Finally, the Petrels’ incubation and foraging patterns might remain the same. The Petrels in heated burrows will then “keep the change” of their extra energy, and put it into growth. Sarah favors the first hypothesis of increased neglect (less time spent in the burrow), while Liam takes the opposite view. It will be the end of the summer before either of them is proved right or wrong, once the eggs hatch and Sarah and Liam can compare the success of Petrels in the heated burrows to the control group.

The task of the afternoon was to process birds in the heated and sham burrows, a procedure that I was familiar with from my adventures with tree swallows. To control for their interference with the birds and the stress that removing and processing them causes, Liam and Sarah try to replicate every procedure in the heated and unheated burrows. Once Sarah, after plunging an arm shoulder-deep into a burrow, had the Petrel nestled safely (but unhappily) in one hand, she gave me the great responsibility of holding the egg. It seemed so unlikely that in a few weeks this fragile, slightly warm orb would be a living, breathing bird, the product of forty days of care. These eggs are especially precious because Petrels only lay one per year, which makes it all the more devastating when inexperienced parents crush an egg or abandon their burrow. After removing the egg from the burrow, Sarah replaced it with a fake egg to keep the burrow temperature consistent. Liam weighed and measured the egg and then its parent, which glared at us resentfully.

Liam Processes a Petrel

Liam Processes a Petrel

Sarah removes a Petrel and its egg from the burrow

Sarah removes a Petrel and its egg from the burrow

Watching Liam measure the birds, which he has described as “mice on wings,” I was impressed by their huge wingspan. Though they are comically clumsy on land, Petrels are agile endurance fliers that spend most of their lives foraging thousands of miles over the sea. “We’re seeing Petrels at their worst,” Liam reminded me after I couldn’t help but chuckle at the Petrel’s pathetic leg waving when it was placed upside down in a toilet paper tube to be weighed.

A Petrel being weighed

A Petrel being weighed

The final step of the process, and Liam’s least favorite, was to pull a tail feather from the parent. Storm Petrel feathers lack the banding that shows growth in other birds, so instead Sarah and Liam will compare the length of the removed feather to that of the tailfeather that grows in to replace it. If the birds from heated burrows have longer feathers, it may indicate that they put their extra energy into growth.

As we walked from the experimental area to the rest of the Shire, where Team Petrel gathers baseline life history data to add to the existing seventy-year record, Liam put the scale of their study into perspective for me. Setting up the twenty burrows involved in the heating experiment and monitoring the 330 burrows that give them demography data is a mountain of work for two people, but at last count there were at least 20,000 pairs of Petrels on Kent Island. Sarah and Liam, like most scientists, can test a relatively small sample size and control for a limited number of variables, leaving plenty of mysteries about how Petrels live and what the future may hold.

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