Effect of endurance flight on haematocrit in migrating birds

Abstract

The effects of an endurance flight on the haematocrit, the percentage of packed red blood cells per blood volume, were examined within the framework of six possible factors explaining possible changes in the haematocrit. Two approaches were adopted: (1) the haematocrit was studied in four species of passerine birds which landed on an Italian island after having crossed the Mediterranean Sea on their spring migration in a non-stop flight; (2) the haematocrit was evaluated in six individual red knots after a flight of 1, 2, 4 and 10 h in a wind tunnel and the data thus obtained compared with data on resting birds with or without food. In the four passerine species, the haematocrit decreased from 51% in fat birds to 48% in lean birds. In lean birds, the haematocrit dropped from 48% in birds with well-developed breast muscles to 36% in birds with emaciated breast muscles. In the red knots, the haematocrit was dependent on body mass in flying and resting birds. The haematocrit decreased from about 51% pre-flight to about 49% within 1 h of flight and remained at this level for up to 10 h of flight. Taking the results from the passerines and the red knots together, it seems that the haematocrit drops by a few percentage points within 1 h after the onset of flight, decreases very slowly with decreasing body mass and decreases more steeply in very lean birds having entered stage III of fasting. This indicates that dehydration is not an underlying factor in decreased haematocrit because if this were the case we would expect an increase with endurance flight. We found no effect of the presence of blood parasites on haematocrit. With the onset of flight, haemodilution may be adaptive, because it reduces blood viscosity and, thereby, energy expenditure by the heart, or it may be a sign of water conservation as an insurance against the risk of dehydration during long non-stop flights. During endurance flight, a reduction in the haematocrit may be adaptive, in that oxygen delivery capacity is adjusted to the decreased oxygen needs as body mass decreases. A decreasing haematocrit would also allow birds to reduce heart beat frequency and/or heart size, because blood viscosity decreases disproportionally with decreasing haematocrit. However, when energy stores are about to come to an end and birds increase protein breakdown, the haematocrit decreases even further, and birds probably become anaemic due to a reduced erythropoiesis.

Social and environmental factors modulate leucocyte profiles in free-living Greylag geese (Anser anser)

“…Hence, the seasonal differences in relation to pair-bond status we found in our study may reflect differences among greylag geese with different bonding status and energetics (De Graw, Kern & King, 1979; Jenni et al, 2006). High H/L ratio may reflect physiological stress produced by competition for partners during the mating season and frequent agonistic interactions among the unpaired individuals, which may not enjoy the stress buffering effect of emotional social support by social allies, notably by a pair partner (Scheiber et al , 2005).…”

Migration phenology and winter habitat quality are related to circulating androgen in a long-distance migratory bird

“…It is unlikely that the elevated haematocrit in early arriving males was due to differential dehydration levels compared with later arrival birds, as birds can quickly restore water lost metabolically during migration within several hours of arrival (Morton 1994). Further, metabolic water loss during migratory flight cannot explain why, for example, bar‐tailed godwits Limosa lapponica increase haematocrit prior to departure from staging areas (Piersma et al 1996), or why red knots Calidris canutus actually decreased haematocrit after being exercised in a wind tunnel (Jenni et al 2006). Jenni et al did show that the slight decrease in hematocrit was associated with migratory flight corresponds to reduction in muscle scores, indicating that birds with high hematocrit are in superior physical condition, however that was not reflected in our analyses of size‐corrected mass.…”

Validation of the use of phenylhydrazine hydrochloride (PHZ) for experimental manipulation of haematocrit and plasma haemoglobin in birds

“…2004) and the physiological basis of variation in parental care, such as chick provisioning; (ii) migration, in both free‐living birds, using telemetry (Wikelski et al. 2003), and in wind‐tunnel experiments with captive birds (Jenni et al. 2006); (iii) metabolic costs of thermoregulation and winter acclimatization (Swanson 1990); and (iv) adaptation to hypoxia at high altitude (Ruiz et al.…”