Long flights do not influence immune responses of a long-distance migrant bird: a wind-tunnel experiment

Abstract

Heavy physical work can result in physiological stress and suppressed immune function. Accordingly, long-distance migrant birds that fly for thousands of km within days can be expected to show immunosuppression, and hence be more vulnerable to infections en route. The red knot Calidris canutus Linnaeus is a long-distance migrant shorebird. We flew red knots the equivalent of 1500 km over 6 days in a wind tunnel. The humoral and cell-mediated immune responses of the flyers were compared to those of non-flying controls. Humoral immunity was measured as antibody production against injected diphtheria and tetanus antigens, and cell-mediated response as phytohemagglutinin-induced wing-web swelling. Blood corticosterone levels, which may modulate immune function, were measured in parallel. The long flights had no detectable effects on humoral or cell-mediated immune responses, or on corticosterone levels. Thus, flight performance per se may not be particularly stressful or immunosuppressive in red knots. Some birds assigned as flyers refused to fly for extended periods. Before flights started, these non-flyers had significantly lower antibody responses against tetanus than the birds that carried out the full flight program. This suggests that only birds in good physical condition may be willing to take on heavy exercise. We conclude that these long-distance migrants appear well adapted to the work load induced by long flights, enabling them to cope with long flight distances without increased stress levels and suppression of immunity. Whether this also applies in the wild, where the migrating birds may face adverse weather and food conditions, remains to be investigated.

Are birds stressed during long-term flights? A wind-tunnel study on circulating corticosterone in the red knot

“…1) is within the range reported in other studies on the same species (10-30 ng/ml; Piersma and Ramenofsky, 1998;Reneerkens et al, 2002). Hence, it seems very unlikely, that the baseline levels were affected by the immune challenge the knots experienced before the flight experiments (Hasselquist et al, 2007). The only other corticosterone data from experimentally controlled physical activity in birds came from domestic birds.…”

“…The pre-and post-experimental baseline levels of the birds flown in the wind-tunnel did not differ from control birds not flown in the wind-tunnel, but kept under the same conditions (Hasselquist et al, 2007). The average baseline corticosterone concentration of the red knots in our study (15.7 before and 14.00 ng/ml after the experimental flights, see Fig.…”

“…Hence, batch 2 had a longer period between trapping and experiment than batch 1, and we therefore entered batch as variable in the statistical analyses. However, for both groups experiments were conducted during the species migration period (batch 1: 11-30 Sept; batch 2: 27 Oct-16 Nov), the birds accumulated high fat levels characteristic of knots in migratory state, and they flew voluntarily for long sessions (2-10 h) in the wind-tunnel (Hasselquist et al, 2007). For details about housing and assigning birds to either a group flown in the wind-tunnel or a control group not flown in the wind-tunnel, see Hasselquist et al (2007).…”

“…However, for both groups experiments were conducted during the species migration period (batch 1: 11-30 Sept; batch 2: 27 Oct-16 Nov), the birds accumulated high fat levels characteristic of knots in migratory state, and they flew voluntarily for long sessions (2-10 h) in the wind-tunnel (Hasselquist et al, 2007). For details about housing and assigning birds to either a group flown in the wind-tunnel or a control group not flown in the wind-tunnel, see Hasselquist et al (2007). Since the birds were also tested for the effect of long flights on immune response, they were injected with a diphtheria-tetanus vaccine two times, the first time one month before flight treatment and the second time just before flight treatment started (for details see Hasselquist et al, 2007).…”

“…For details about housing and assigning birds to either a group flown in the wind-tunnel or a control group not flown in the wind-tunnel, see Hasselquist et al (2007). Since the birds were also tested for the effect of long flights on immune response, they were injected with a diphtheria-tetanus vaccine two times, the first time one month before flight treatment and the second time just before flight treatment started (for details see Hasselquist et al, 2007). Details about the Lund wind-tunnel and the flight performance of red knots can be found in Pennycuick et al (1997), Lindström et al (2000), Kvist et al (2001) and Jenni-Eiermann et al (2002).…”