Wild geese do not increase flight behaviour prior to migration

Abstract

Hypertrophy of the flight muscles is regularly observed in birds prior to long-distance migrations. We tested the hypothesis that a large migratory bird would increase flight behaviour prior to migration, in order to cause hypertrophy of the flight muscles, and upregulate key components of the aerobic metabolic pathways. Implantable data loggers were used to record year-round heart rate in six wild barnacle geese (Branta leucopsis), and the amount of time spent in flight each day was identified. Time in flight per day did not significantly increase prior to either the spring or the autumn migration, both between time periods prior to migration (5, 10 and 15 days), or when compared with a control period of low activity during winter. The lack of significant increase in flight prior to migration suggests that approximately 22 min per day is sufficient to maintain the flight muscles in condition for prolonged long-distance flight. This apparent lack of a requirement for increased flight activity prior to migration may be attributable to pre-migratory mass gains in the geese increasing workload during short flights, potentially prompting hypertrophy of the flight muscles.

Figure 1.

(a–f) Time in flight per day throughout the annual cycle of six barnacle geese. The year is split into seven distinct cycles: (1) winter, (2) pre-spring migration, (3) spring migration, (4) breeding, (5) wing moult, (6) pre-autumn migration and (7) autumn migration. The seven phases are highlighted in (a). The difference in duration of the spring and autumn migration is well documented in barnacle geese [15].

Figure 2.

Mean (±s.e.m.) time in flight per day by six barnacle geese during winter, compared with flight time (days) between periods prior to the (a) spring and (b) autumn migration.