ESKIMO CURLEW SEARCH CONTINUES

This mount of an Eskimo Curlew taken in Connecticut is one of the only specimens known from this state.

The admittedly Quixotic search for surviving Eskimo Curlews that might still migrate through outermost coastal Massachusetts entered its second year this August.  Bird Conservation Research, Inc. continues to search habitats not traditionally scanned by bird watchers seeking migrating shorebirds. One tantalizing possibility is that bird move through each fall undetected because the birdwatching community has forgotten how to look for the species. We focus our efforts on sand flats and dune hollows where 19th century gunners once hunted curlews. We avoid searching the tidal mudflats used by the majority of other shorebird species.

Although the probability of success in finding a curlew is low, previous similar efforts by BCR Director Robert Craig have ultimately yielded success. In searching for the supposedly extinct Aguiguan Reed-warbler, knowing how to look for the species made all the difference in successfully relocating it. Similarly, learning how to look for the Black Rail led to its rediscovery as a Connecticut summer resident after 14 years of searching.

VARIABLE CIRCULAR PLOT SURVEYS FOR AP ENVIRONMENTAL SCIENCE

In the VCP technique, observers measure the horizontal distance from a survey point to the location of individual animals.

Forest bird surveys conducted by Bird Conservation Research, Inc. use the variable circular plot technique (VCP)- a very sophisticated and powerful tool used in field surveys of animal populations. It is the method employed by most technically advanced wildlife studies, and is the field method underlying the BCR bird population estimates (see previous BLOG) made in Connecticut and Rhode Island.  During the eight years of this study, high school science students were involved in computerizing and analyzing the enormous volumes of data gathered (50,172 bird observations and 19,980 habitat measurements!).


To educate students into the utility of VCP, we have developed a lab investigation for AP Environmental Science that leads them through the steps of gathering field data.  This investigation moves from collection of field data to computing population densities using DISTANCE software.  Data gathered from VCP are entered into DISTANCE and turned into densities of species per square km.

STATE OF THE FOREST BIRDS OF CONNECTICUT: PRELIMINARY ESTIMATES AND ACTUAL NUMBERS

The Northern Waterthrush has larger regional populations than preliminary estimates

indicated.

The Connecticut State of the Birds 2011 report contained a contribution from Bird Conservation Research, Inc. entitled State of the Forest Birds.  In this report we projected, based on our findings for eastern Connecticut and Rhode Island, the total populations of certain species.  Since the appearance of our contribution, we have completed computerization of all of our data and are now able to estimate with accuracy populations present during the years of our study.  Although our analyses are undergoing further refinement by using new features available in Distance 6.0, our population estimation software, we can now make the following comparisons between preliminary Connecticut projections and actual estimates based on all data.
 Yellow-bellied Sapsucker: projected– most common woodpecker in northwestern CT, actual– 20,968 vs. 11,958 for the Downy Woodpecker.


Acadian Flycatcher: projected– 10,000, actual– 10,413.


Least Flycatcher: projected– 3,000, actual– 4,281.

Black-billed Cuckoo: projected– 1,000, actual– 411–815 in differing years.

Yellow-billed Cuckoo: projected– 1,000, actual- 2,156-4,354 in differing years.

Common Raven: projected– 400, actual– 395.

Cerulean Warbler: projected- 6,000, actual– 6,105.

Black-throated Blue Warbler: projected– 10,000+, actual– 41,712.

Pine Warbler: projected– 20,000+, actual– 74,431.

Louisiana Waterthrush: projected– 20,000, actual– 23,337.

Northern Waterthrush: projected– 3,000, actual– 4,190.

Eastern Towhee: projected– approaching 100,000, actual– 64,196.

Differences between initially projected and actual numbers are largely attributable to eastern Connecticut not always serving as a good model for populations in the rest of the state. This was particularly true in the case of the towhee, which had high densities in eastern Connecticut and Rhode Island but low densities elsewhere.

POPULATION ESTIMATION LAB FOR AP ENVIRONMENTAL SCIENCE

This figure shows the detection probability of Black-throated Blue Warblers encountered at increasing distances from an observer.  It was generated using program DISTANCE.

Population estimation as traditionally taught in AP Environmental Science is simplistic and does not take into account species detectability or population changes due to immigration, emigration, mortality and natality.  Lab activities also make little use of free software available for estimating populations.  The software DISTANCE and MARK are are used for estimating populations, respectively, from large scale surveys and from mark-recapture projects.


To introduce teachers and students to more sophisticated methods of population estimation that go beyond the simple but unrealistic Lincoln-Peterson method, we have developed two laboratory investigations that use the 1) Jolly-Seber method, that computes populations by taking into account population changes that occur over time, and 2) Distance sampling (using the variable circular plot technique), that computes populations by accounting for differences in species detectability encountered during field surveys.  Both investigations may be found under the Educators tab of the Bird Conservation Research, Inc. web site.