Eikenaar Cas, Ostolani Alessia, Brust Vera, Karwinkel Thiemo, Schmaljohann Heiko, Isaksson Caroline
Institute of Avian Research "Vogelwarte Helgoland", 26386, Wilhelmshaven, Germany.
Department of Biology, University of Pisa, 56126, Pisa, Italy.
Mov Ecol. 2023 Feb 6;11(1):7. doi: 10.1186/s40462-023-00372-7.
Birds have extremely elevated metabolic rates during migratory endurance flight and consequently can become physiologically exhausted. One feature of exhaustion is oxidative damage, which occurs when the antioxidant defense system is overwhelmed by the production of damaging reactive oxygen species (ROS). Migrating birds have been shown to decrease the amount of oxidative lipid damage during stopovers, relatively stationary periods in between migratory flights. It has therefore been argued that, in addition to accumulating fuel, one of the functions of stopover is to restore the oxidative balance. If this is so, we would expect that migrating birds are unlikely to resume migration from stopover when they still have high amounts of lipid damage.
To test this hypothesis, we measured parameters of the oxidative balance and related these to stopover departure decisions of song thrushes (Turdus philomelos) and northern wheatears (Oenanthe oenanthe), a medium- and long-distance songbird migrant, respectively. We measured malondialdehyde (MDA) concentration, a biomarker for oxidative lipid damage, and total non-enzymatic antioxidant capacity (AOX), an overall biomarker of protection against ROS. Stopover departure decisions were determined using a fully automated telemetry system set-up on our small island study site.
The decision to resume migration was not related with MDA concentration in either study species, also not when this was corrected for circulating fatty acid concentrations. Similarly, AOX did not affect this decision, also not when corrected for uric-acid concentration. The time within the night when birds departed also was not affected by MDA concentration or AOX. However, confirming earlier observations, we found that in both species, fat individuals were more likely to depart than lean individuals, and fat northern wheatears departed earlier within the night than lean conspecifics. Northern wheatears additionally departed earlier in spring with more southerly winds.
We found no support for the idea that stopovers departure decisions are influenced by parameters of the oxidative balance. We discuss possible reasons for this unexpected finding.
鸟类在持久的迁徙飞行过程中代谢率极高，因此可能会出现生理疲劳。疲劳的一个特征是氧化损伤，当抗氧化防御系统被具有破坏性的活性氧（ROS）的产生所压倒时就会发生这种情况。研究表明，候鸟在中途停歇期间（即迁徙飞行之间相对静止的时期）会减少氧化脂质损伤的量。因此，有人认为，中途停歇的功能之一除了积累能量外，还在于恢复氧化平衡。如果真是这样，我们预计当候鸟仍有大量脂质损伤时，它们不太可能从中途停歇地恢复迁徙。
为了验证这一假设，我们测量了氧化平衡参数，并将这些参数与歌鸫（欧歌鸫）和白斑黑石鵖（一种分别为中长途迁徙的鸣禽）从中途停歇地出发的决定相关联。我们测量了丙二醛（MDA）浓度（一种氧化脂质损伤的生物标志物）和总非酶抗氧化能力（AOX，一种对抗ROS的总体保护生物标志物）。使用我们在小岛上的研究地点设置的全自动遥测系统来确定从中途停歇地出发的决定。
恢复迁徙的决定与两个研究物种的MDA浓度均无关，在对循环脂肪酸浓度进行校正后也是如此。同样，AOX也不影响这一决定，在对尿酸浓度进行校正后同样如此。鸟类在夜间出发的时间也不受MDA浓度或AOX的影响。然而，正如早期观察所证实的那样，我们发现，在这两个物种中，肥胖个体比瘦个体更有可能出发，并且肥胖的白斑黑石鵖在夜间比瘦的同种个体出发得更早。此外，春季南风较大时，白斑黑石鵖出发得更早。
我们没有找到证据支持中途停歇地出发决定受氧化平衡参数影响这一观点。我们讨论了这一意外发现的可能原因。
