Development of an Interior Least Tern Monitoring Working Group

ERDC TN-DOER-E17

September 2004

How important are areas that support low numbers of ILTs? (abundance).

What is the relative accuracy of different count methods currently in use? (abundance).

How many visits are necessary and what methods are needed to estimate the number of

fledglings? (productivity).

To what extent is dispersal information necessary and how do we obtain that informa-

tion? (distribution and productivity).

What is the relative value of having information on post-fledgling dispersal, survival, and

habitat needs? How might this information be obtained? (distribution and productivity).

How much interchange is there between coastal and inland populations?

What is the status of winter populations? Virtually nothing is known about wintering

individuals.

Several methodologies exist that may provide estimates of the number of visits necessary to

obtain good information on productivity. Information on dispersal is also needed, but birds are

wide-ranging and difficult to resight. Information on post-fledgling dispersal, survivorship, and

habitat needs may be necessary for use in a population viability analysis (PVA), but it will be

difficult to obtain this information cheaply, easily, or reliably. Such efforts will require extensive

banding (and even more extensive resighting) efforts and detailed information on movement of

individual birds. These data may be useful in determining whether the interior population is sus-

tained by (or growing due to) immigration of birds from coastal areas.

Questions raised: How valid is modeling if coverage is not complete? Can modeling be con-

ducted using only count data? These questions are not easily answered, but by sub-sampling the

population, good estimates of breeding adults and good productivity data can be obtained and

used in population modeling. However, if a complete census of the population can be obtained,

then population modeling may not be necessary, because all pertinent information on the popu-

lation status would already be available. The ILT population presents an opportunity to obtain a

complete census, although this would require an increase from current survey efforts.

Some answers may be obtained by analyzing existing long-term data sets to determine best pro-

tocols. This could be accomplished by comparing data sets from large and small colonies, and

areas utilizing different productivity protocols. However, productivity is highly variable; meas-

uring productivity per nesting attempt is probably useless because birds may attempt to nest

many times during the season. Conducting surveys two or more times a season will likely be

insufficient to accurately assess an individual bird's productivity. Furthermore, lifetime repro-

ductive success of individuals is difficult, if not impossible, to obtain. Yet, useful data can still be

obtained from both detailed coverage of abundance and distribution, and cursory methods to

estimate productivity (perhaps conducting two visits per colony on a subset of colonies).

Development of an Interior Least Tern Monitoring Working Group: To facilitate the

development of a standardized monitoring protocol for ILT populations, an ILT Monitoring

Working Group (WG) was established (Table 1). This group includes individuals from govern-

ment agencies (Corps, USFWS, and USGS), the ABC, and several state agencies and universi-

ties. A small subset of these individuals agreed to act as an Executive Working Group (EWG)