Avian Demographic Data from the Colville River Delta, Alaska

For information on first arrivals, trained observers collected information on the daily occurrence of bird species during the course of normal field activities. This included compiling daily species checklists. The date of first arrival of the most common species at these two field sites was compiled across the years for which we collected these data.

For nest monitoring, we determined the initiation date of each nest. If a nest was found during laying, we estimated initiation date by back-dating by the number of eggs found at discovery based on published estimates of egg-laying rates for each species (Alisauskas and Ankney 1992, Sandercock 1998, Hussell and Montgomerie 2020). For nests found with a complete clutch, we used an egg candling technique (Weller 1956) for Black Brant and Lesser Snow Geese, and an egg floatation technique (Liebezeit et al. 2007) for Semipalmated Sandpipers. For Lapland Longspur nests that were found with complete clutches, we were only able to estimate initiation dates for nests that subsequently hatched, wherein we back-dated from the hatch date based on the nest’s clutch size and application of a 12-day incubation period (Hussell and Montgomerie 2020). We recorded the clutch size (maximum number of eggs) and hatching success of nests. Based on these measures, we applied species-specific incubation periods to estimate hatch dates.

For chick growth, we collected repeat measures of body mass from hatch until fledge on chicks of Semipalmated Sandpipers and Lapland Longspurs from 2015–2017. For Semipalmated Sandpipers, we visited nests at hatch and banded the chicks with uniquely numbered U.S. Geological Survey metal bands. Chicks departed the nest shortly after hatch, and we attempted to recapture Semipalmated Sandpiper chicks at 5-day intervals, but also collected mass measurements when we opportunistically encountered broods. Lapland Longspur chicks were too small to retain leg bands at hatch, so we did not uniquely mark Longspur chicks. We visited Longspur nests and weighed chicks as soon as possible after the first egg in each nest hatched, and weighed chicks at approximately 3-day intervals thereafter. For both of these species, the sex of the chicks was unknown. We weighed the chicks of both species with electronic balances accurate to ±0.1 g.