Scientists at Fargo, ND have studied 83 species of birds for their arrival time over ten years. The study concluded that the majority of arriving earlier than they did historically. The uniqueness of this study is that they measured FAD (First arrival dates) and AGDU (Accumulated growing degree units). The accumulated growing degree units for a time of arrival deviated from past values as much as 4-5% higher or lower depending on the species. As a whole, short distance migrants have advanced arrival times and reduced AGDU as compare to long distance migration birds (Travers, S et al. 2015)
Authors studied first arrival dates of 93 species of migrants in …show more content…
Ecological mismatches have also affected the bird populations. Timing of bird’s spring migration is important for conservation efforts and birds which are not able to adjust phenology for changes will decline in population (Elizabeth R.E et.al)
Many authors have provided evidence that ecological factors such as climate have the carryover effect on individuals and population processes in next seasons. The effects are limiting population sizes; Precipitation has been observed to have the effect on spring arrival and nest initiation dates of European migrants. Poor winter habitat results in poorer body condition during migration and delayed spring arrival in temperate breeding grounds. Later breeding dates, reduced and lower return rates of migratory birds.
Differences in food availability across nonbreeding season habitats affect multiple measures of overwintering migratory bird performance, including site persistence, body condition, and Corticosterone levels.(Rockwell,S et.al 2012)
Factors affecting timing of nesting