Avian migration phenology and global climate change

Abstract

There is mounting evidence that global climate change has extended growing seasons, changed distribution patterns, and altered the phenology of flowering, breeding, and migration. For migratory birds, the timing of arrival on breeding territories and over-wintering grounds is a key determinant of reproductive success, survivorship, and fitness. But we know little of the factors controlling earlier passage in long-distance migrants. Over the past 30 years in Oxfordshire, U.K., the average arrival and departure dates of 20 migrant bird species have both advanced by 8 days; consequently, the overall residence time in Oxfordshire has remained unchanged. The timing of arrival has advanced in relation to increasing winter temperatures in sub-Saharan Africa, whereas the timing of departure has advanced after elevated summer temperatures in Oxfordshire. This finding demonstrates that migratory phenology is quite likely to be affected by global climate change and links events in tropical winter quarters with those in temperate breeding areas.

Fig. 1.

Mean (–SE) slopes of linear regressions for 20 species of migrant bird in Oxfordshire from 1971 to 2000. (a) Arrival date, departure date, and duration of stay in Oxfordshire against time. (b) Winter SOI, winter NAOI, and winter surface air temperature anomaly for Africa south of 20°N against arrival date in Oxfordshire. (c) Summer NAOI, Oxford summer maximum temperature, and Oxford summer minimum temperature against departure date from Oxfordshire. Significance of one-sample t test of mean slope vs. null hypothesis of no effect (slope = 0); *, P < 0.05; **, P < 0.01; ***, P < 0.001.

Fig. 2.

Linear regressions on the arrival date (filled circles, solid line) and departure date (open circles, dashed line) of Northern House Martins, Delichon urbica, in Oxfordshire, from 1971 to 2000. Arrival date: slope = –0.671, r² = 0.243, P < 0.08. Departure date: slope =–0.647, r² = 0.207, P < 0.02. There is no significant difference between the two slopes (t = 0.101, d.f. = 54, P > 0.05).