Blackcaps during migration make nutritional choices depending on their infection status

Submitted by Michi on 23 April 2024.

Avian haemosporidian parasites infect the blood of a great diversity of birds, having many consequences for their physiology and performance. Infections may increase the oxidative stress of hosts due to the metabolism of the parasites and the activation of the immune response of the birds. Infected birds could potentially alleviate this additional oxidative stress through adaptive feeding, targeting antioxidant-rich foods.

In their study, Lucía Jiménez-Gallardo and co-authors investigated the diet of young male Eurasian blackcaps (Sylvia atricapilla) during their stop-over in central Spain on the autumn migration. Birds were held temporarily and offered two experimental foods - one fat-enriched (providing energy) and the other anthocyanin-enriched (providing antioxidants). Birds were videoed to determine their individual preference between the two.

                        Disposition of a cage where blackcaps found two food offers: a piece of melon soaked in cranberry juice (anthocyanin-enriched) on the left, and another soaked in olive oil (fat-enriched) on the right.

Blood samples were then taken to determine the birds infection status (with respect to Haemoproteus, Plasmodium, and Leucocytozoon parasites), and to assess oxidative damage (red blood cells and plasma malondialdehyde, which is lipid damage), antioxidant markers (total glutathione and antioxidant capacity of plasma), and other controlling variables (protein content, uric acid, and triglycerides).

                              The authors Javier Pérez-Tris and Lucía Jiménez-Gallardo processing blackcaps at the stopover site.

Many of the 48 birds tested were found to be infected with either a single (28 birds), or multiple (14 birds) type of haemosporidian parasite. They found that birds with infections by multiple parasites significantly preferred the anthocyanin-enriched food.

Infected birds had a lower antioxidant capacity of their plasma, compatible with the idea that antioxidants are being physiologically consumed at a greater rate due to the immune challenge against the infection. Finally, Jiménez-Gallardo and co-authors found that individuals with evidence of more oxidative damage detected in their plasma also preferred anthocyanin-enriched food.

                             A stopover site in central Spain within an olive grove.

Together their study suggests that during the energetically and physiologically challenging autumn migration, male blackcaps make strategic nutritional choices which can help to protect them against oxidative stress and the costs of parasitic infection.

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