New gecko progeny

The 5th and 6th offspring from Wren and Atticora:

View my previous offspring and pictures of the parents here.

Isotopes and the Discovery of a Winter Range

In a paper by Russel Greenberg et al., the authors used isotope analysis of feathers grown during the winter molt to identify the previously unknown wintering grounds of a subspecies of Swamp Sparrow. The Coastal Plain Swamp Sparrow (Melospiza georgiana nigrescens) is a species of coastal marshes from New York to Virginia.

The subspecies is visibly diagnosable by plumage: in breeding by having heavier black markings, a general gray-brown color on the flanks, lower back and rump, and a larger bill. In winter it is distinctive in its olive-brown rather than rusty-brown color, and larger bill.

Coastal Plain Swamp Sparrow
(Photo source)

'Regular' Swamp Sparrow

(Photo source)

Feathers, when grown, can take up the isotopic signature of various elements in their environment (such as isotopes of Carbon, Nitrogen, and Hydrogen, studied here). Maps of the various isotopic gradients across the US have been studied, with a coarse-grade level of detail. We can analyze the isotope signatures of a feather and make a reasonable inference about the latitude at which the bird grew that feather. There are also isotopic differences for elevation, coastal vs. inland, etc.

The authors used the isotope concentrations of the rump feathers grown during the fall by the Swamp Sparrows and from male crown feathers grown from in late winter to generate an overlapping map of the three isotopes examined and narrow the likely location for the winter range of nigrescens to the coastal region of the Carolinas and southern Virginia. The authors then followed up their prediction by surveying coastal marshes in this window of prediction, finding 17 nigrescens in marshes in North Carolina and southern Virginia:

The authors cite one previous instance of using isotopes to identify a possible unknown winter range (Acrocephalus paludicola, Pain et al. 2004) but they believe they are the first to use isotopes to predict and then discover a population’s wintering ground. The use of isotopes often yields too coarse-grade results for useful inference, but when it succeeds the results can be very informative, as seen here.

Reference:

Greenberg, R., Marra, P.P., Wooller, M.J. (2007). STABLE-ISOTOPE (C, N, H) ANALYSES HELP LOCATE THE WINTER RANGE OF THE COASTAL PLAIN SWAMP SPARROW (MELOSPIZA GEORGIANA NIGRESCENS). The Auk, 124(4), 1137. DOI: 10.1642/0004-8038(2007)124[1137:SCNHAH]2.0.CO;2

A Unique Foraging Mechanism in Shorebirds

In a remarkable paper by Sora M. Estrella et al., the authors demonstrate the widespread use of a feeding mechanism in shorebirds known as surface-tension transport. The shorebirds draw a small prey item within a drop of water up the bill, without the assistance of suction or movement of the tongue. Instead, they utilize the surface tension of water to wick the droplet up to their mouth by slightly spreading their mandibles. This mechanism was first proposed and then demonstrated in the lab in Red-necked

Phalaropes by Rubega and Obst (1993):

If the proper balance were struck between cohesion of the drop and its adhesion to the bird's beak, progressive mandibular spreading would increase the amount of potential energy stored in the surface of the drop by increasing the free surface area of the drop. Because physical systems move to reduce potential energy (unless this tendency is opposed), the drop would move in the direction that was most likely to reduce free surface area. As long as drop positions more proximal to the gape result in smaller free surface areas and, hence, lower energy states, than those at the distal end of the bill, the drop should move toward the buccal cavity.

In other words, the droplet of water held in the bill sticks to both mandibles. As the jaws spread, the droplet is stretched out. This creates tension, which forces the droplet up the bill to reduce the distance between mandibles and the surface tension of the droplet. Rubega and Obst filmed phalaropes in the lab, using both living birds capturing prey, and specimen bills to test the mechanism and successfully eliminated tongue movement and suction as potential explanations: the dead bill still draws water drops with no tongue movement, and living birds demonstrated no throat pumping associated with sucking water up the bill.

Rubega and Obst’s laboratory studies have shown this mechanism can take less than a tenth of a second! This mechanism is discussed by both Rubega and Obst (1993) and Estrella et al. (2007) in terms of feeding efficiency, in that it allows shorebirds to feed on small prey items rapidly and with minimal energy expenditure in prey handling.

Estrella et al. (2007) extended the laboratory studies to the field, recording a total of six species in the wild (Little Stint, Dunlin, Sanderling, Curlew Sandpiper, Common Redshank, Black-winged Stilt; the study are was in Spain) adding to the four species shown in the lab to demonstrate STT (Red-necked Phalarope, Wilson’s Phalarope, Western Sandpiper, Least Sandpiper) to give a total of at least ten species in two families demonstrating this very interesting feeding method. It is very likely to be widespread in the shorebirds as a group.

This field study begans to illustrate the constraints of bill structure on the use of STT hypothesized by Rubega and Obst (1993). Estrella et al. (2007) observed Redshank and Stilt using head jerks to assist the motion up the bill. The bill must gradually widen towards the head for STT to work, and the authors note that Redshank and Stilt have fairly uniform narrow bill widths along their length.

Interestingly enough, their data shows variability by species in time per cycle (one opening movement of the bill, several cycles necessary to draw all the way up the bill) but the overall total transport time per prey item does not vary according to bill length. This indicates internal bill morphology dictates differences in STT function between species, not overall bill length.

This is a fascinating feeding mechanism that I was previously unaware of. With the demonstration by Estrella et al. (2007) of surface tension transport’s widespread use in the field, the door is open for many more novel and interesting studies on bill morphology and foraging bioenergetics with shorebirds.

Finally, go here for some truly excellent photography of shorebirds demonstrating STT.

References:

Estrella, S.M., Masero, J.A., Perez-Hurtado, A. (2007). SMALL-PREY PROFITABILITY: FIELD ANALYSIS OF SHOREBIRDS' USE OF SURFACE TENSION OF WATER TO TRANSPORT PREY. The Auk, 124(4), 1244. DOI: 10.1642/0004-8038(2007)124[1244:SPFAOS]2.0.CO;2

Margaret A. Rubega and Bryan S. Obst. 1993. Surface-tension feeding in phalaropes: discovery of a novel feeding mechanism. The Auk. 110(2): 169-178. April 1993. (PDF)

Oct 2007 Auk: Lance-tailed Manakin Displays

Another interesting paper in this October's Auk is Emily DuVal's characterization of the displays and call types of the Lance-tailed Manakin (Chiroxiphia lanceolata) of southern Central America. Manakins (Pipridae) are known for the elaborate displays of males on lek. Some species (Club-winged Manakin) even have modified wings to produce structure buzzing and clicking sounds in display.

(Photo by Emily Duval. Source)

The Lance-tailed Manakin exhibits the unusual trait of cooperative male displays on leks. Males cooperate in pairs to display for females, with one of the males being 'alpha' and continuuing the display on to copulation. To help examine the evolution of this mating system, DuVal characterized by components the behavioral and vocalization components of the manakin's display.

Another prominent example of component-level analysis of complex displays has recently been published by Ed Scholes, who has filmed the displays of many species of Birds-of-Paradise. DuVal's analysis complements her work on understanding why the helper males cooperate when they don't sire young. See her recent American Naturalist paper for more information.

References:

Emily H. DuVal. 2007. Adaptive advantages of cooperative courtship for subordinate male lance-tailed manakins. American Naturalist. 169: 423-432. April 2007.

Emily H. DuVal. 2007. Cooperative display and lekking behavior of the Lance-tailed Manakin (Chiroxiphia lanceolata). The Auk 124(4): 1168-1185. October 2007. (Abstract)

So cute! But so wrong! But so cute!

I found this blog via Pharyngula - The Daily Coyote, in which a woman is raising an orphaned coyote pup in her home. Peruse through the whole archive - the pup is adorable, and I love her pictures and captions, as well as her remarks about its behavior and interaction with her cat.

However, the more I read the blog the more I cringe. She has taken an orphaned wild pup and is raising it as a trained pet. She has completely humanized it. This action, to begin with, is something that I cannot condone - many wildlife orphans are rehabbed and released every year. It is not right to adopt one as a pet, and is very likely illegal (I am unaware of what protections are in place on canids, although she often talks about coyotes being shot on sight in the area so maybe there are no significant protections).

However, it gets worse. She maintains no illusions that this is a wild animal and will likely need to be released as it matures - see posts here and here. She maintains there are safe places she could let him loose, but there is no place for this animal now. She has doomed it to die if she releases it now. She has trained it to recognize, respond to, and be part of 'the pack' with humans. Even if this animal is still perfectly capable of surviving in the wild on its own, any contact with humans will end in disaster for the animal.

So, enjoy the cute pictures, but remember what these actions to save a cute orphan have done.