Relationship between energetic condition and indicators of immune function in thrushes during spring migration

Evidence suggests that the ability of an animal to maintain its immune system and (or) mount an immune response depends on its nutritional health and energetic condition. Migration is a period within an animal's annual cycle when energetic condition varies, especially after a long, nonstop flight over a large ecological barrier. Our objective was to determine if measures of immune function in migrating Wood Thrush (Hylocichla mustelina (J.F. Gmelin, 1789)), Swainson's Thrush (Catharus ustulatus (Nuttall, 1840)), Gray-cheeked Thrush (Catharus minimus (Lafresnaye, 1848)), and Veery (Catharus fuscescens (Stephens, 1817)) were related to the energetic condition of the birds at a stopover site during spring migration. We present data on total leukocyte, lymphocyte, and heterophil counts, heterophil/lymphocyte ratio, serum immunoglobulin gamma G (IgG) concentration, and immune response to phytohemagglutinin. Thrushes arriving at the stopover site in poor energetic condition had low leukocyte and lymphocyte counts. Heterophil/lymphocyte ratio, heterophil count, and IgG concentration were not related to energetic condition. Furthermore, immune response to phyto- hemagglutinin was positively related to change in mass and days spent in captivity, suggesting that immune function may improve during stopover. We suggest that migrating thrushes arriving at a stopover site in poor energetic condition may also be in poor immunological condition and may have increased susceptibility to disease or parasite infection. Resume´ : Des donnees indiquent que la capacited'un animal amaintenir son systeme immunitaire et(ou) adevelopper une reaction immunitaire depend de sa santealimentaire et de sa condition energetique. La migration represente une peri- ode dans le cycle annuel d'un animal pendant laquelle les conditions energetiques varient, particulierement apres un long vol ininterrompu de migration a travers une importante barriere ecologique. Notre objectif est de determiner si les me- sures de la fonction immunitaire chez des grives des bois (Hylocichla mustelina (J.F. Gmelin, 1789)), des grives ados olive (Catharus ustulatus (Nuttall, 1840)), des grives a joues grises (Catharus minimus (Lafresnaye, 1848)) et des grives fauves (Catharus fuscescens (Stephens, 1817)) en migration sont reliees ala condition energetique des oiseaux a un site d'arret durant leur migration printaniere. Nous presentons des donnees sur les denombrements totaux de leucocytes, de lymphocytes et d'heterophiles, sur le rapport heterophiles/lymphocytes, sur la concentration d'immunoglobuline gamma G (IgG) serique et sur la reaction immunitaire ala phytohemagglutinine. Les grives qui arrivent au site d'arrete n mauvaise condition energetique ont des denombrements bas de leucocytes et de lymphocytes. Le rapport heterophyles/ lymphocytes, le denombrement d'heterophiles et l'IgG ne sont pas reliesala condition energetique. De plus, la reaction immunitaire ala phytohemagglutinine est en correlation positive avec le changement de masse et le nombre de jours de garde en captivite ´, ce qui laisse croire que la fonction immunitaire peut s'ameliorer durant l'arret. Nous croyons que les grives en migration qui arrivent au site d'arret en mauvaise condition energetique peuvent aussi etre en mauvaise condi- tion immunologique et etre plus vulnerables a la maladie ou aux infections parasitaires. (Traduit par la Redaction)