Birding News & Views

The Eyes Have It

Pecten: A Unique Structure In The Eyes Of Birds

by Howard Topoff


How much energy does it take to see? The visual system is one of the most energetically demanding systems in the brain. Although seeing obviously doesn't require the energy of running a marathon, the millions of rods and cones in the retina use quite a bit of oxygen and nutrients to convert light into nerve impulses and transmit them to the brain. So you will not be surprised that the human retina (and that of most animals) is infiltrated with a large supply of blood vessels. After all, it's the blood that carries oxygen and nutrients to all retinal cells. But all these blood vessels create their own problem: they block some of the light from reaching the retina.


Birds, which are even more visually dominant than humans, have solved this problem in a most unusual way. The retinas in their eyes contain NO blood vessels - they are avascular. So, the $64.00 question is: how do the eyes of birds, which are among the best developed in the animal world, function without these vital molecular supplies? The answer is their retinas ARE supplied with oxygen, amino acids, sugars, and all necessary nutrients, but not from blood vessels in the retina. Instead, birds have evolved a truly unique structure called the PECTEN.


The Pecten (see diagram) consists of folded tissue and is filled with melanin granules ( the same pigment that darkens our skin and hair - well, it used to darken MY hair). It projects from the retina into the vitreous, is well supplied with blood vessels and keeps the retina supplied with oxygen and nutrients.


Scientists still have a lot to learn about this mysterious structure and have hypothesized several additional interesting functions. For example:


1. Slight warming of pecten due to absorption of light by melanin granules enhances the secretion of nutrients into the vitreous, eventually to be absorbed by the bird's avascular retina.


2. The pecten may shade the retina from dazzling light or aid in detecting moving objects. And since it contains melanin, it may lessen stray light entering the bird eye to reduce background glare.


3. You probably heard of the blood-brain barrier. The cells of the capillaries in the brain are so tightly joined that many (especially toxic) substances are prevented from diffusing into brain cells. Turns out the capillaries in the pecten also have these "tight junctions," so the pecten might constitute a blood-retina barrier, keeping harmful substances out of the bird's retina.


When it comes to relative size, visual acuity, and spectral sensitivity, the eyes of birds are truly unique. The evolution of the PECTEN is just one additional adaptation that gives new meaning to the term "Bird Brain.”

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2015 Chiricahua Mountains Elegant Trogon Census
Date: Thu Jun 4 2015 15:24 pm - From: rtaylor AT borderland-tours.com


Ten Elegant Trogons, 7 males, 3 females were recorded by 43 volunteer counters in the Chiricahua Mountains May 31, 2015 on the annual Chiricahua Mountain Elegant Trogon Census. All 10 trogons were located in the South Fork-Cave Creek Canyon complex where 38 counters in 21 contiguous riparian areas recorded all audio and visual observations in 5 minute increments from 6 a.m. until 11 a.m. in assigned territories that averaged approximately 0.5 mile in length. Only one male trogon was not in South Fork Cave Creek. It was in the main trunk of Cave Creek between Sunnyflat Campground and the Southwestern Research Station. Rucker Canyon and East Turkey Creek were also visited by 5 counters in 2 survey teams, but no trogons were found in either drainage.

Because female Elegant Trogons call less and are less visually conspicuous than their mates, and because they spend most of the morning incubating or brooding when they have nests, they are are easily overlooked. It is possible that survey teams missed 1 or more female trogons on the 2015 survey. Male trogons are usually detected on this census, but an effort was made not to double-count males that visited adjacent survey territory during the 5-hour-long count period. The 2015 tally of 10 trogons in the Chiricahua Mountains on May 31 is meant to be an irreducible minimum number present on that day.

As in the past several years, no trogons were heard or seen above the SW Research Station up to the Herb Martyr Picnic Area in the Snowshed (or Main Fork) of Cave Creek, up to Ash Spring in the Cima Creek Fork, and for 1.5 miles above the SW Research Station in North Fork Cave Creek. These areas have all historically harbored breeding trogons. There were not enough volunteers to survey East Whitetail Canyon, Price Canyon, John Long Canyon, or Pine Canyon, all canyons where trogons have also been recorded historically, although not with regularity.

10 represents the highest number of Elegant Trogons in the South Fork-Cave Creek Canyon complex since the 2011 Horseshoe Two Fire. Last year there were 9. There were 13 trogons all in the South Fork-Cave Creek Canyon complex on the 2010 census (no other canyons were surveyed in 2010). In the 1990s most surveys conducted with the same methodology and similar numbers of volunteer counters turned up approximately 20 trogons.

Reasons for the low trogon population in the Chiricahua Mountains in recent years seem to be related to habitat degradation, perhaps attributable to the the 223,000 acre Horseshoe Two Fire and the subsequent flooding, as well as a long-term drought that began in 1994 which seemingly ended last summer with above average rainfall during the 2014 monsoon. Elegant Trogon populations in all 4 other border ranges surveyed for this species, the Atascosa, Santa Rita, Patagonia, and Huachuca Mountains, seemed to be stable or gradually increasing in 2015.

Counters were also asked to record any additional species sharing Elegant Trogon habitat. Excluding Elegant Trogons, altogether 60 species were reported in South Fork and the main trunk of Cave Creek between Stewart Campground and the SW Research Station. If the upper tributaries of Cave Creek are included in the tally areas where no trogons were found this year or on the previous 4 census years the associative bird community number climbs to 80 species. The lowest number of other species present in the trogon census area in the South Fork-Cave Creek Canyon complex was in 2012, when only 59 other species were reported. In 2013 some 76 additional species were found in habitats used by trogons. Probably as a consequence of the 223,000 acre Horseshoe Two Fire in 2011, the number of associative species seen that year was 82, the highest number ever recorded on a Chiricahua Mountains Elegant Trogon Census.

Mexican Jay was the single species most apt to be seen in the South Fork-Cave Creek Canyon complex in 2015; counters recorded this species in 21 survey territories. Other species that seemingly define trogon habitat in the complex included Acorn Woodpecker (18 surveyor territories), Plumbeous Vireo (17), Black-headed Grosbeak (17), and White-breasted Nuthatch, American Robin, and Painted Redstart (all found on 15 territories). All of these species may reasonably be supposed to occur on all of the survey territories. Oddly, no Coopers Hawks were seen during the 5 count period hours, and for the first time in 5 years no Buff-breasted Flycatchers were found. Buff-breasted Flycatchers were, however, recorded on the survey in Rucker Canyon.

Probably the most unusual bird on the census was an adult Common Black Hawk photographed in North Fork Cave Creek. Common Black Hawks were recorded on the previous 2 Rucker Canyon surveys, but none were seen there this year.

I personally wish to express my gratitude to everyone who helped with the 2015 Chiricahua Mountains Elegant Trogon Census. Special thanks are owed to Jennie MacFarland, IBA coordinator for the Tucson Audubon Society, for recruiting the volunteer census-takers. Thanks also to the Douglas Ranger District of the Coronado National Forest for the use of the USFS Portal Visitor Information Center, and for waiving campground fees for some surveyors who only arrived the night before the census.

Rick Taylor,
Compiler

The North American Migration Count

(Courtesy Of Mike Williams)


The North American Migration Count (NAMC) was started in 1992 to give bird watchers the opportunity to enjoy a day's birding during spring migration with the knowledge that the results of their findings, together with the birds counted by others, would reveal the status of bird migration on a specified date. The goals of the NAMC are to get a picture of the progress of spring migration and to obtain data on the abundance and distribution of each migratory species.


(Mexican Chickadee by Robert Shantz) (Thick-Billed Kingbird by Maya Decker)


The Migration Count for Cochise County was held on Saturday, May 9th. 211 species were seen, the highest in a decade. In the Portal area, including up to Rustler, 10 people and 1 tour group were checking birds at feeders and in the field. We saw 132 species and 2423 total birds. 10 of the 132 were only seen in our part of the county. These 10 were:

Band-tailed Pigeon Blue-throated Hummingbird

Cassin's finch Mexican Chickadee

Peregrine Falcon Pygmy Nuthatch

Red-Naped Sapsucker Rufous-backed Robin

Tropical Kingbird White-throated Sparrow


There were 20 species that the majority of the species were seen in our count area of the county. These included Brown-crested Flycatcher, Elf Owl, Gambel's Quail (below) Magnificent Hummingbird and Northern Cardina


(Cecil Williams)


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Willow Tank - Helping A Critical Wildlife Sanctuary

by Alan Craig

It is critical tokeep water in Willow Tank to provide wildlife habitat. One wouldhave to camp outat the tank to fully appreciate how manybirds, bats and critters use the water at WT, let alone the foodand cover the vegetation provides. During the 2+ months ofSpring migration and a much longer period during Fallmigration, those birds that migrate by day may stop onlybriefly for a drink or to grab a few insects before continuingout of sight en route to their nesting or wintering grounds.



It is owned by the Larry River's family and we owe a big thankyou to them for their extensive financial and physical help inkeeping this vital water source open.

Cecil Wiiliams

Willow Tank is open to bird watchers. There is water onlyin the deep end now as the banks and reinforcing is completed. There will be multiple viewing stations and stairs, which will be completed in the next month or so, followed by the refilling.

A few days ago there were 4White-faced Ibis feeding on the pond along with a pair ofMexican Ducks.

Check it out!


WT is on Sulphur Canyon Rd. west off of Stateline Road just asStateline intersects U.S. 80.

Friends of Cave Creek Canyon strongly believes in preserving and improving this valuable resource. We have made a sizeable donation and encourage you to also help. For more information, contact Alan Craig at 520-558-2220 oracraig@me.com

Howard Topoff 2011