Could nestling condition indicate a changing habitat?

A seven-day old LOWA nestling is getting its bands! These plastic bands, which in no way harm the birds, allow me to visually track the nestlings once they fledge (leave the nest) and identify them if they return the following breeding season. When we band nestlings, we also measure wing length and mass so we can calculate nestling [health] condition.

In the case of the nestling below, bands enabled me to confirm a resight of a fledged juvenile from this nest later in the season. The juvenile had traveled over 1.2 km downstream then another 3 km upstream along different rivers outside its natal territory.

 

During 2015 banding for MAPS (Monitoring Avian Productivity and Survivorship, a national program) at Tremont, we caught several juveniles I banded as nestlings that season and gave them full adult band combinations. The juvenile below fledged from a nest 2.5 km from the MAPS net it was caught in. If this LOWA returns to my study sites, I'll be able to individually identify it and know it's natal nest site/territory area.

 

If my research finds a relationship between LOWA reproductive success and hemlock health (e.g., nest failure is associated with lower hemlock health), we could hypothesize hemlock decline leads to inadequate food resources for LOWA. Measuring nestling condition will allow us to compare nestling health against hemlock health and test hypotheses about potential driving mechanisms behind the LOWA/hemlock relationship(s).