Prokaryotic and Eukaryotic Cells

The Difference between Prokaryotes and Eukaryotes

There are only two basic types of cells, primitive prokaryotes and the more complex eukaryotes. Here are the main features that distinguish these cell types.

What Is a Cell?

Living things are constructed of cells and can be unicellular (one cell) or multicellular (many cells).

Limits on Cell Size

Cells size is limited because cells must be able to exchange materials with their surroundings. In other words, surface area relative to the volume decreases as size of cell increases, and this limits the size of cells.

Cell Theory

Only a few hundred years ago it was believed that living things could spontaneously generate from non-living matter -- abiogenesis. We now know better. Cell theory lays out the basic rules that apply to these smallest units of life. This cell doctrine states that:

• All organisms are composed of one or more cells.
• Cells are the basic unit of structure and function in organisms.
• All cells come only from other cells.

Two Basic Types of Cells

All cells fall into one of the two major classifications: prokaryotes or eukaryotes.

Prokaryotic Cells

Prokaryotes are evolutionarily ancient. They were here first and for billions of years were the only form of life. And even with the evolution of more complex eukaryotic cells, prokaryotes are supremely successful. All bacteria and bacteria-like Archaea are prokaryotic organisms.

Eukaryotic Cells

Eukaryotic cells are more complex, evolving from a prokaryote-like predecessor. Most of the living things that we are typically familiar with are composed of eukaryotic cells; animals, plants, fungi and protists. Eukaryotic organisms can either be single-celled or multi-celled.

Features of Prokaryotes

Pro = “before”, karyon = “nucleus”

Prokaryotes, the first living organisms to evolve, are primarily distinguished by the fact that they lack a membrane bound nucleus. Their genetic material is naked within the cytoplasm, ribosomes their only type of organelle.

Prokaryotes are most always single-celled, except when they exist in colonies. These ancestral cells, now represented by members of the domains Archaea and Eubacteria, reproduce by means of binary fission, duplicating their genetic material and then essentially splitting to form two daughter cells identical to the parent.

Features of Eukaryotes

Eu = “true”, karyon = “nucleus”

The most noticeable feature that differentiates these more complex cells from prokaryotes is the presence of a nucleus, a double membrane-bound control center separating the genetic material, DNA (deoxyribonucleic acid), from the rest of the cell.

Eukaryotic cells also contain internal membrane-bound structures called organelles. Organelles, such as mitochondria and chloroplasts, are both believed to have evolved from prokaryotes that began living symbiotically within eukaryotic cells. These vital organelles are involved in metabolism and energy conversion within the cell. Other cellular organelles within eukaryotic cell structure carry out the many additional functions required for the cell to survive, thrive, grow and reproduce.

Eukaryotic cells can reproduce in one of several ways, including meiosis (sexual reproduction) and mitosis (cell division producing identical daughter cells).

Sexual Reproduction

As discussed in part one of this series about asexual reproduction, reproduction is a marvelous culmination of individual transcendence. Individual organisms come and go, but, to a certain extent, organisms "transcend" time through reproducing offspring. This week, we'll take a look at sexual reproduction.

Sexual Reproduction

In sexual reproduction, two individuals produce offspring that have genetic characteristics from both parents. Sexual reproduction introduces new gene combinations in a population.

Image credit: U.S. Fish and Wildlife Service

Gametes

In animals, sexual reproduction encompasses the fusion of two distinct gametes to form a zygote. Gametes are produced by a type of cell division called meiosis. The gametes are haploid (containing only one set of chromosomes) while the zygote is diploid (containing two sets of chromosomes). In most cases, the male gamete, called the spermatozoan, is relatively motile and usually has a flagellum. On the other hand, the female gamete, called the ovum, is nonmotile and relatively large in comparison to the male gamete.

Human Ovum(Egg) and Sperm Image credit: Copyright Dennis Kunkel

Types of Fertilization

There are two mechanisms by which fertilization can take place. The first is external (the eggs are fertilized outside of the body); the second is internal (the eggs are fertilized within the female reproductive tract).

Patterns and Cycles

Reproduction is not a continuous activity and is subject to certain patterns and cycles. Oftentimes these patterns and cycles may be linked to environmental conditions which allow organisms to reproduce effectively. For example, many animals have estrous cycles that occur during certain parts of the year so that offspring can typically be born under favorable conditions. Likewise, these cycles and patterns can be controlled by hormonal cues as well as other seasonal cues like rainfall. All of these cycles and patterns allow organisms to manage the relative expenditure of energy for reproduction and maximize the chances of survival for the resulting offspring.

Related Resources
• Asexual Reproduction
• Reproduction II
• Meiosis

Article Source : http://biology.about.com

Asexual Reproduction

From Regina Bailey,

Reproduction is a marvelous culmination of individual transcendence. Individual organisms come and go, but, to a certain extent, organisms "transcend" time by reproducing offspring. Let's take a look at reproduction in animals.

What is reproduction?

In a nutshell, reproduction is the creation of a new individual or individuals from previously existing individuals. In animals, this can occur in two primary ways: through asexual reproduction and through sexual reproduction. Let's look at asexual reproduction.

Gemmules of the freshwater sponge spongilla. Image courtesy of J. Houseman; BIODIDAC

Asexual Reproduction

In asexual reproduction, one individual produces offspring that are genetically identical to itself. These offspring are produced by mitosis. There are many invertebrates, including sea stars and sea anemones for example, that produce by asexual reproduction. Common forms of asexual reproduction include:

Budding

• In this form, an offspring grows out of the body of the parent.
  
  
• Hydras exhibit this type of reproduction.
  
  
  Hydra Budding
  Image courtesy of BIODIDAC

Gemmules (Internal Buds)

• In this form, a parent releases a specialized mass of cells that can develop into an offspring.
  
  
• Sponges exhibit this type of reproduction.
  
  
  Sponge Gemmmules
  Image courtesy of BIODIDAC

Fragmentation

• In this form, the body of the parent breaks into distinct pieces, each of which can produce an offspring.
  
  
• Planarians exhibit this type of reproduction.
  
  
  
  Planarian
  Image courtesy of BIODIDAC

Regeneration

• In this form, if a piece of a parent is detached, it can grow and develop into a completely new individual.
  
  
• Echinoderms exhibit this type of reproduction.
  
  
  
  Oral surface of a star fish.
  Image courtesy of BIODIDAC

Taxonomy

From Regina Bailey,

Taxonomy is a hierarchical system for classifying and identifying organisms. This system was developed by Swedish scientist Carolus Linnaeus in the 18th century.

Binomial Nomenclature

Linnaeus's taxonomy system has two main features that contribute to its ease of use in naming and grouping organisms. The first is the use of binomial nomenclature. This means that an organism's scientific name is comprised of a combination of two terms. These terms are the genus name and the species or epithet. Both of these terms are italicized and the genus name is also capitalized.

For example, the scientific name for humans is Homo sapiens. The genus name is Homo and the species is sapiens.

These terms are unique and no other species can have this same name.

Classification Categories

The second feature of Linnaeus's taxonomy system that simplifies organism classification is the ordering of species into broad categories. There are seven major categories: Kingdom, Phylum, Class, Order, Family, Genus, and Species.

A good aid for remembering these categories is the mnemonic device: Keep Plates Clean Or Family Gets Sick.

Some of these categories can be further divided into intermediate categories such as subphyla, suborders, superfamilies, and superclasses. An example of this taxonomy scheme is:

Kingdom

Phylum
Subphylum
Superclass
Class
Subclass
Superorder
Order
Suborder
Superfamily
Family
Subfamily
Genus
Subgenus
Species
Subspecies

Brain differences may herald drug addiction

By C. Brownlee | Mar 3, 2007

Differences in the behavior and the brain receptors of rats seem to predict which of the rodents will become cocaine addicted, scientists report. The finding supports the idea that some people are predisposed to drug addiction.

Scientists have long suspected that certain personality traits, including thrill seeking, impulsivity, and a tendency to be antisocial, go hand in hand with drug addiction. Studies have also shown that the brains of monkeys and people addicted to stimulants such as cocaine or amphetamine have significantly fewer receptors for dopamine, a brain chemical that regulates emotion, motivation, and feelings of pleasure.

However, the connection between these mental and physical characteristics and drug addiction has posed a chicken-and-egg problem for researchers. It's unclear whether drug addicts have these qualities before they begin using drugs or whether taking drugs over the long term changes a person's personality and brain properties.

Jeffrey Dalley of the University of Cambridge in England and his colleagues report results in the March 2 Science that shed light on this problem. The researchers taught a group of lab rats to poke their noses in a hole to retrieve a treat after seeing a light flash. The team found that about 7 percent of the animals consistently acted impulsively. Rather than wait to collect the treat that appeared after the light blinked, those animals frequently poked their noses into the hole before the treat arrived.

Dalley's team next scanned the rats' brains. In a region known as the nucleus accumbens, the impulsive animals had significantly fewer of the D2/3 type of dopamine receptor than the more patient rats did. Previous studies in people had connected the nucleus accumbens to reward feelings, such as those gained from eating, winning at gambling, and taking drugs.

Finally, the researchers hooked the impulsive and normal animals to a machine that delivered cocaine intravenously when the rats pressed a lever. The impulsive animals learned to self-administer the drug more quickly and took more of it than the other rats did. Within days, the impulsive rats were using cocaine at nearly twice the rate of the patient ones.

Because the impulsive rats had fewer D2/3 receptors before using drugs, Dalley says, the traits of impulsivity and a low number of these D2/3 receptors seem to be characteristics that make an animal vulnerable to drug addiction.

David Jentsch of the University of California, Los Angeles, who studies the long-term effects of drugs on the brain, calls the study "very exciting." He adds, "This will help us understand what leads people on a pathway to drug abuse."

Jentsch cautions that it's premature to say that all people who become addicts had pre-existing anomalies in personality and brain traits. Rather, long-term drug use may cause these anomalies in some people who didn't have them before.

"It's unlikely that it's an either-or phenomenon," Jentsch says.

COPYRIGHT 2007 Science Service, Inc.
Copyright 2007, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company.

Road Map to the Kingdoms of Life

A look at the major kingdoms of life.
Related Resources • Botany • Microbiology • Zoology Do Protista, Monera or Animalia sound familiar? If not, don't fret and get ready to explore the familiar and not so familiar forms of life. Organisms are classified into one of six Kingdoms of life. They are placed into these categories based on similarities or common characteristics. Use the Classification of Life chart below to find out information, examples, and characteristics of each of the kingdoms. Just click on the image of the kingdom you would like to know more about. (Since archaea were previously classified as monera, information on archaea can be found under monera.)

Study finds human medicines altering marine biology

Southern California toxicology researchers find chemicals from wastewater are ending up in coastal oceans -- and affecting the hormone levels of fish.

By Kenneth R. Weiss, Los Angeles Times Staff Writer

BOSTON -- Sewage-treatment plants in Southern California are failing to remove hormones and hormone-altering chemicals from water that gets flushed into coastal ocean waters, according to the results of a study released Saturday.

The preliminary findings were part of the most ambitious study to date on the effect of emerging chemical contaminants in coastal oceans. It confirms the findings of smaller pilot studies from 2005 that discovered male fish in the ocean were developing female characteristics, and broadened the scope of the earlier studies by looking at an array of man-made contaminants in widespread tests of seawater, seafloor sediment and hundreds of fish caught off Los Angeles, Orange and San Diego counties.

The results, outlined by a Southern California toxicologist at a conference in Boston, reveal that a veritable drugstore of pharmaceuticals and beauty products, flame retardants and plastic additives are ending up in the ocean and appear to be working their way up the marine food chain.

Flame retardants used in upholstery and plastic additives are showing up in fish tissues at levels as high or higher than lingering residue of the banned pesticide DDT and another stubborn industrial pollutant, polychlorinated biphenyls, or PCBs.

The study also showed that male flatfish contain unusually high levels of the female hormone estrogen, possibly in reaction to one or more of these hormone-altering chemicals.

As many as 90% of these male fish were found to have produced egg yolk proteins, and one had actually produced eggs, indicating that the feminizing of fish seen in freshwater streams and lakes can happen in the open ocean as well. This evidence, scientists said, suggests that diluting pollution with a vast amount of seawater may not be an effective way to dispose of these new and little-understood contaminants.

"Dilution is not the solution for some of these newer compounds," said Steven Bay, a toxicologist with the Southern California Coastal Water Research Project in Costa Mesa. He expects the study to raise policy debates over upgrading sewage-treatment plants.

Although some of these contaminants may be in urban runoff, the main source appears to be the 1 billion gallons of partially treated sewage that flows into the ocean every day from the region's four major sewage outfalls.

Women taking birth control pills excrete estrogen in their urine, which is flushed down the toilet and ends up in the ocean. The same is true of antidepressants, tranquilizers, anti-inflammatory medicine and other drugs, as well as musk fragrances, sunscreens, soaps and additives to plastics -- compounds known to mimic or disrupt hormones.

"Sewage-treatment plants only remove 50% to 70% of these chemicals," Bay said.

Bay sketched out the preliminary results in a special session at the annual meeting of the American Assn. for the Advancement of Science.

Much of Saturday's discussion focused on sex-changing chemicals in municipal wastewater. "It doesn't take much of the pill to stop fish from reproducing," said Karen Kidd, a biology professor at the University of New Brunswick in Canada.

Kidd said sewage plants could remove virtually all estrogen with more advanced forms of treatment.

Primary treatment, the type used in San Diego, doesn't take out as much estrogen as secondary treatment, used by Los Angeles' Hyperion plant in El Segundo. Those plants, if upgraded to tertiary treatment, could remove nearly all of the estrogen, Kidd said.

Another study looked at how compounds used as fabric stain repellents, nonstick pan coatings and coatings in microwave popcorn bags have accumulated in the blood and tissue of loggerhead sea turtles. They are suppressing the immune systems of these turtles, which are officially designated as threatened with extinction.

The sea turtles pick up these compounds through what they eat, said Jennifer M. Keller, a researcher with the National Institute of Standards and Technology. "They eat crabs and clams and other shellfish -- a diet they share with humans."

The study in Southern California waters looked at contaminants in wastewater, surrounding ocean waters, sediments and in the flesh of 600 flatfish called hornyhead turbot.

These bottom-dwelling fish were selected because they reside near sewage outfalls.

The results showed that the chemicals and responses from the fish were widespread and not confined to areas near sewage outfalls, showing how easily the chemicals get dispersed.

Besides elevated estrogen levels in male fish, test results showed altered thyroid hormone levels in the turbot. They also had depressed cortisol levels, an indication that the fish were worn out and are vulnerable to disease.

So far, Bay said, no evidence has emerged that the chemicals are threatening their survival or ability to reproduce.

From Los Angeles Times

The medium-/long-chain fatty acyl-CoA dehydrogenase (fadF) gene of Salmonella typhimurium is a phase 1 starvation-stress response (SSR) locus

BY : MP Spector, CC DiRusso, MJ Pallen, F Garcia del Portillo,
G Dougan and BB Finlay

Department of Biomedical Sciences, University of South Alabama, Mobile 36688, USA. mspector@usamail.usouthal.edu

Salmonella enterica serovar Typhimurium (S. typhimurium) is an enteric pathogen that causes significant morbidity in humans and other mammals. During their life cycle, salmonellae must survive frequent exposures to a variety of environmental stresses, e.g. carbon-source (C) starvation. The starvation-stress response (SSR) of S. typhimurium encompasses the genetic and physiological realignments that occur when an essential nutrient becomes limiting for bacterial growth. The function of the SSR is to produce a cell capable of surviving long-term starvation. This paper reports that three C-starvation-inducible lac fusions from an S. typhimurium C-starvation-inducible lac fusion library are all within a gene identified as fadF, which encodes an acyl-CoA dehydrogenase (ACDH) specific for medium-/long-chain fatty acids. This identification is supported by several findings: (a) significant homology at the amino acid sequence level with the ACDH enzymes from other bacteria and eukaryotes, (b) undetectable beta-oxidation levels in fadF insertion mutants, (c) inability of fad insertion mutants to grow on oleate or decanoate as a sole C-source, and (d) inducibility of fadF::lac fusions by the long-chain fatty acid oleate. In addition, the results indicate that the C-starvation-induction of fadF is under negative control by the FadR global regulator and positive control by the cAMP:cAMP receptor protein complex and ppGpp. It is also shown that the fadF locus is important for C-starvation-survival in S. typhimurium. Furthermore, the results demonstrate that fadF is induced within cultured Madin-Darby canine kidney (MDCK) epithelial cells, suggesting that signals for its induction (C-starvation and/or long-chain fatty acids) may be present in the intracellular environment encountered by S. typhimurium. However, fadF insertion mutations did not have an overt effect on mouse virulence.

The in vitro morphogenetic capacity of olive embryo explants at different developmental stages, as affected by L-Glutamine, L-Arginine and 2,4-D

BY : T. S. PRITSA and D. G. VOYIATZIS

The role of exogenously applied L-glutamine (Gln) and L-arginine (Arg) in growth (dry weight), cell division (callus induction) and differentiation (spherical structure formation), of cotyledonary explants of olive embryos, cv. Chondrolia Chalkidikis, at three developmental stages, and of fully developed embryos, was investigated, in relation to the presence of auxin in the nutrient medium. The percentage of explants forming spherical structures increased with the advancement of the embryo development and was particularly high in the absence of auxin. Histological examination showed these structures to be either somatic embryos at an early stage of development or organ initials. The presence of Arg generally inhibited growth and morphogenetic capacity of explants. Glutamine up to 500 mg.L^-1 did not affect growth but in most cases improved slightly callus induction. There was a significant, negative correlation between the cumulative concentration of the two amino acids and the parameters measured.

Ultrastructure of pericarp development in Gracilaria verrucosa (Hudson) Papenfuss (Gracilariaceae, Gracilariales, Rhodophyta)

BY : S. G. DELIVOPOULOS

The ultrastructure of pericarp development in Gracilaria verrucosa (Huds.) Papenfuss is described. Anticlinal and successive periclinal divisions of the outer cortical cells result in the formation of a thick multilayer pericarp. Primary pit connections occur between pericarp cells. Mucilage is formed within cytoplasmic concentric membranes, giving thus rise to mucilage sacs. In addition, mucilage sacs seem to arise through local dilations of the nuclear envelope. Mucilage sacs considerably increase in volume resulting in the formation of one or two huge mucilage sacs, which occupy the major part of the cell interior and finally discharge their contents. Thus, inner pericarp cells actually function as secretory cells exhibiting a degenerate appearance after the release of the content of mucilage sacs.

Charophytes from four Cyclade Islands (Mykonos, Naxos, Paros and Antiparos) in Greece

BY : A. LANGANGEN

I have shortly described eleven localities from the Cyclade islands Mykonos, Naxos, Paros and Antiparos, one of which has freshwater, two have brackish water and the rest are salt lakes. Of special interest are the salt lakes. These lakes are situated close to popular beaches and are therefore exposed to human activities. The lakes at Ag. Prokopios, Kamari, Mikra Vigli, Naxos airport and Fanari beach should be protected. The brackish water lake near the airport at Naxos has special qualities and should also be protected. The charophytes Lamprothamnium papulosum, Chara canescens, C. galioides and C. aspera were found in this lake. Typical species in the salt lakes are Lamprothamnium papulosum and Ruppia maritima. The salt content in these lakes varied between 1.3% (2003) and 20% (2002). In such environments, L. papulosum can only survive by oospores and/or bulbils. In Kamari, I found specimens of L. papulosum with swollen lower branchlets. In the brackish water poll at Ormos Amiti I found Chara vulgaris, while Chara globularis was found in freshwater on Mykonos. Totally six species of charophytes have so far been found in the islands.

Chemotaxonomic significance of leaf wax n-alkanes in the Pinales (Coniferales)

BY : M. MAFFEI, S. BADINO and S. BOSSI

The chemotaxonomic significance of leaf wax n-alkanes was studied in 112 species and cultivars belonging to the Pinaceae, Cupressaceae, Podocarpaceae, Araucariaceae, Cephalotaxaceae, Sciadopityaceae and Taxaceae (Pinales). In general, n-alkanes ranged from 18 to 34 carbon numbers. In the Pinales, C₃₁ was the most abundant n-alkane (20.17%±1.68), followed by C₂₇ (2.84%±0.41), C₂₉ (2.59%±0.49) and C₂₅ (2.41%±0.22). In the Araucariaceae, n-alkane composition was characterized by low relative percentages of C₃₁ (5.23%±1.58), whereas the Cephalotaxaceae were characterized by high percentages of C₂₉ (31.95%±2.05) and C₂₇ (28.00%±1.00). The Cupressaceae had a mean composition of n-alkanes characterized by moderate percentages of C₃₁ (18.31%±2.32) and C₃₃ (5.36%±1.07), whereas in the Pinaceae, C₃₁ was the main n-alkane (25.40%±2.56). The Podocarpaceae were characterized by moderate percentages of C₂₉ (12.69%±9.16), C₃₁ (10.77%±2.70), C₂₇ (7.37%±5.83) and C₃₃ (6.59%± 5.71), whereas the Taxaceae had high percentages of C₃₁ (34.94%±7.85). Sciadopitys verticillata showed low percentages of all n-alkanes. Discriminant Analysis (DA) of the Araucariaceae, Cupressaceae and Pinaceae showed a good discrimination among subfamilies. Cluster Analysis (CA) and Principal Component Analysis (PCA) performed on species of the Pinales, showed a good separation among the families. The direct comparison of the present data with those obtained on species belonging to eleven angiosperm families provided further evidence of the chemotaxonomic significance of leaf wax n-alkanes.

From Journal of Biological Research

Establishing a bio-monitoring program of plant species and habitats of the Mesogaia area (Athens, Greece)

SOFIA SPANOU1, GEORGIOS VERROIOS1, GEORGIOS DIMITRELLOS1, ARGYRO LIVANIOU-TINIAKOU1, THEODOROS GEORGIADIS1* and ANASTASIOS ANAGNOSTOPOULOS2 1 Botanical Institute – Plant Ecology, Department of Biology, University of Patras, GR 265 00, Patras, Greece 2 Athens International Airport S.A., Wildlife & Landscaping Environmental Services Department, GR 190 19, Spata, Greece

Ever-increasing human activities in the Mesogaia area (prefecture of Attiki, Greece) have caused severe environmental disturbances and alteration of the area’s natural ecosystems. The construction and operation of the new Athens International Airport “Eleftherios Venizelos” in the area is expected to amplify these disturbances directly or indirectly. Bio-monitoring of the remaining natural habitat types is of high importance; therefore, a research project was established in order to monitor any impacts induced by the construction and operation of the new International Airport and the prospective development of the surrounding area. A detailed survey of the flora and vegetation of the area and vegetation mapping enabled the authors to identify and record the habitat types, plant communities and the area’s ecosystem dynamics, as well as to evaluate anticipated environmental impacts. Subsequently, a number of plant taxa connected with conservation references are presented here, along with several habitat types considered important for plants and animals.

From Journal of Biological Research

Population density and food analysis of Bombina variegata and Rana graeca

BY : RIKA BISA, SPYROS SFENTHOURAKIS, STELLA FRAGUEDAKIS-TSOLIS and BASIL CHONDROPOULOS Section of Animal Biology, Department of Biology, University of Patras, Panepistimioupoli 265 00 Rio, Greece

Abundance and diet of Bombina variegata and Rana graeca were investigated from August 2004 to August 2005 in two permanent mountain water bodies (Zesto River and Prioni Nazeti Stream) situated in the National Park of Northern Pindos (Greece). At Zesto, we recorded high population densities for both anuran species, while at Nazeti population density was high only for R. graeca. In the diet of B. variegata and of R. graeca, a large variety of prey taxa was identified in the stomach contents, suggesting that they are opportunistic predators. However, at both sites, the study species principally consumed five prey groups, i.e. ants, spiders, flies, terrestrial beetles and aquatic insect larvae. A comparison of prey size consumed by adults revealed that B. variegata feeds on smaller prey than R. graeca. Furthermore, intraspecific differences based on prey size were obtained for adults and sub-adults of R. graeca. In this study we found that prey size is a possible factor of niche partitioning for anuran species.

Gone walkabout? Movement of the eastern long-necked turtle Chelodina longicollis

BY: MICHELLE RYAN and SHELLEY BURGIN College of Health and Science, University of Western Sydney, Locked Bag 1797, South Penrith Distribution Centre, New South Wales, Australia

Many freshwater turtle species maintain site fidelity. Short term studies (1-4 years) of the eastern long-necked turtle Chelodina longicollis have shown that turtles moved among water bodies, but some were later recaptured at the dam of initial capture. No long-term studies have been undertaken to determine if site fidelity is maintained. In this paper we re-visited farm dams, initially surveyed a decade previously, and sampled turtles to determine the extent to which C. longicollis maintained site fidelity. Only 11.9% (n=572) of turtles were recaptured. We then expanded the search (from 1 km to 2 km radius of core of original survey site) for marked individuals, and found one marked individual among 179 additional captures. Overall <10%>–1. Population structure in 1995-1996 and 2006 was similar, which indicated that the change was not due to loss of aged individuals and recruitment of young, but to an overall turnover of individuals. We concluded that C. longicollis turtles do not maintain site fidelity over extended periods. Although shown to navigate accurately during fine weather, C. longicollis turtles frequently move during inclement weather and we suggest that they become disoriented due to a lack of environmental queues, and thus take up residence in ‘new’ wetlands.

Help! A robin is bonking into my window!

Copyright by Ann Cook

The Questions

Every year people write letters to Journey North asking for help because a bird — usually a robin — is flying into their window, patio door, or car mirror, over and over and over. The people are sometimes irritated by the noise, and usually worried about the bird. The window often gets smeared with feathers and even blood. What are these robins doing? What can we do to stop this behavior?

The Story

When American Robins start feeling territorial each year, they do their best to keep other adults of the same sex outside of their territorial boundaries. When a territorial robin notices its reflection in a window or mirror within its territory, it gets agitated, raises the feathers on its head, and assumes a dominant posture. Normally that is enough to make any other robins leave the territory immediately. But instead of flying away, the reflected robin seems to get equally agitated, raises its head feathers, and gets in an equally dominant posture. The first time this happens, the real robin often just leaves. If it's a male, he often goes to his favorite song perch and starts singing. When he doesn't hear a responding song, he's more certain that this is really his own territory. If it's a female, she goes back to her daily activities and stays on the lookout for other females.

If the robin sees that reflection again, it gets more and more agitated — but so does the reflection! Finally, the robin flies in to chase the other robin away. But the reflection flies in exactly the same way, and the robin hits the glass. And the reflected robin STILL doesn't leave! No matter how aggressive the real robin gets, and no matter how hard it fights, the reflection matches it. The real robin becomes more and more determined to drive that upstart away!

The Answer

Robins are not stupid. But during the nesting season their territorial urge is even more powerful than their urge to eat or sleep. Defending their territory is the way they ensure there will be enough food for their babies. No wonder they work so hard!

But the whole time the robin is fighting its reflection, it is NOT doing the things that will really ensure its babies' survival. It needs to eat, sing (if it's a male), build a nest, incubate eggs (if it's a female), and chase REAL robins away. How can we help it stop this behavior?

The only way to do this is to break the reflection. Fortunately, we don't have to break the window to do this! The simplest way, if it's a small window or mirror, is to simply tape some paper or cardboard over it, on the outside. Usually the paper needs to be up for three or four days until the robin gets busy enough with other things to forget about the "intruder." If it's a big patio window, it's harder to cover the whole thing. One technique that sometimes works is to paper over the area where the robin has been actually hitting, and then hang shiny helium balloons nearby. Most birds are frightened of helium balloons, probably because they act so different from things birds encounter in nature: they seem to fall up!