Consuming omega-3 fatty acids (n3-LCPUFAs) during development improves cognition in mammals, but the effect remains untested in other taxa. In aquatic ecosystems, n3-LCPUFAs are produced by phytoplankton and bioaccumulate in the food web. Alarmingly, the warming and acidification of aquatic systems caused by climate change impair n3-LCPUFA production, with an anticipated decrease of 80% by the year 2100. We tested whether n3-LCPUFA consumption affects the physiology, morphology, behaviour, and cognition of a top marine predator's chicks, the ring-billed gull. Using a colony with little access to n3-LCPUFAs, we supplemented siblings from 22 fenced nests with opposite treatments from hatching until fledging; one sibling received n3-LCPUFA-rich fish oil and the other, a control sucrose solution without n3-LCPUFAs. Halfway through the nestling period, half the chicks receiving fish oil were switched to the sucrose solution to test whether n3-LCPUFA intake remains crucial past the main growth phase (chronic versus transient treatments). Upon fledging, n3-LCPUFAs were elevated in the blood and brains of chicks receiving the chronic treatment, but were comparable to control levels among transient chicks. Across the entire sample, chicks with elevated n3-LCPUFAs in their tissues fledged earlier despite their morphology and activity levels being unrelated to fledging age. Fledging required chicks to escape fences encircling their nest. We therefore interpret fledging age as a possible indicator of cognition, with chicks with improved cognition fledging earlier. These results provide insight into whether declining dietary n3-LCPUFAs will compromise top predators' problem-solving skills, thus, their ability to survive in a rapidly changing world.

We tested whether supplementing gull chicks with omega-3 long-chain polyunsaturated fatty acids (n3-LCPUFAs) in a context of natural deficiency improved their cognitive development. Using a colony of ring-billed gulls (Larus delawarensis) nesting in an urban environment with no access to food rich in n3-LCPUFAs, we supplemented siblings daily from hatching until fledging with one of three supplemental treatments: the control group received a sucrose solution daily from hatching until fledging, the chronic group received fish oil rich in n3-LCPUFAs daily from hatching until fledging, and the transient group received fish oil daily from hatch until 22 days old before being switched to the sucrose solution daily until fledging. The chicks were otherwise provisioned by their parents at their nest. We monitored their weight gain daily from hatch until 22 days old and weekly thereafter and we confirmed the incorporation of the supplement in their tissues via the fatty acid analysis of blood samples taken at 15 and 36 days old. We also analyzed the fatty acid profile of their cerebral hemispheres at fledging age (42 days old, subsample n=12). We analyzed their activity behaviours during cognitive testing through the number of steps they took and the time they spent trying to escape the testing enclosure. We also recorded their fledging age and interpreted it as a measure of the chicks' cognitive development since fledging required them to escape the fencing surrounding their nests, with improved cognition leading to earlier fledging. 

Here we include the two datasets used for the analysis described in this paper:

Lamarre et al. 2021_repeated_measures: Includes the concentrations of targetted fatty acids in the chicks' red blood cells collected at 15 and 36 days old as well as all mass data points (chicks weighed daily from hatch until 22 days old and weekly afterwards).

Lamarre et al. 2021_non-repeated_measures: Includes the concentrations of targetted fatty acids in the red blood cells of chicks at 36 days old and in cerebral tissues at 42 days old. Also included: chicks' fledging age, hatch and fledging dates, behaviours during the string-pull test (activity and escape) recorded at 35-37days old and averaged, and the mass gained between hatch and 36 days old. 

Both data detailed the chicks identification, treatment group, and hatching order. 

We also include the R script used to statistically analyze our data and validate the resulting models. 

Dataset Lamarre et al. 2021_repeated_measures: A few mass data points are missing due to bad weather preventing access to the colony during a few days.

Dataset Lamarre et al. 2021_non-repeated_measures: Fledging age missing from 2 subjects as they died in their nest at 38 days old (attacked) prior to fledging. The concentrations of targetted fatty acids in the red blood cells of one subject are missing because this individual fledged at 34 days old and could not be recaptured prior to the blood sample collected at 36 days old. Likewise, the behaviours of two individuals could not be assessed during the string-pull tests at 36 days old due to escaping the testing enclosure or fledging before the test took place.