The Nutritional Ecology of Bird Migration

 

I attended a lecture by Dr. Susan Smith on her research related to migrating birds and berry nutrition. Migratory birds spend up to four months a year in the process of migration. These migrations are to wintering grounds and breeding grounds. During these trips, physiological demands are much greater. These trips require very large energy reserves. 79 percent of these reserves come from fats.

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These stores of energy are depleted and then restored at migratory stopovers. At these sites, refueling occurs. This must be rapidly done due to time constraints (must get to wintering ground before winter). Bird’s diets change during migration to be able to rapidly refuel. Birds eat large amounts of fruit. The benefits of eating fruit in place of their normal diet are fruit is high in fat and fruit is easier to hunt. There are limits birds have to eating fruit. One type of limitations are digestive. Bird’s digestive systems can only handle a certain amount of seed load. Also, some fruits contain a certain amount of toxins and the system can handle only so much. Other limitations are nutritional.

Fruit varies in energy and protein content. Some contain up to 40 percent fat, most of these include native species. As fat content increases, energy density also increases. A hermit thrush (Catharus guttatus) (that on average weighs 31.2 grams) would have to eat 18.8 grams of bayberry (Myrica sp.) (high in fat) or 90.7 grams of pokeweed (Phytolacca decandra) to fill the daily energy needs. Eating this much pokeweed is clearly not possible.

 

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A hermit thrush (Catharus guttatus)

 

One of Dr. Smith’s studies tried to see if birds prefer certain fruits during autumn migration time. Nets were placed around berry bushes and the amount that natural falls off was measured. The nets were removed and the amount of berries eaten during different times of the year was measured. The amount of arrowwood (Viburnum dentatum) (high in fat) eaten increased during migration, were as the amount of chokeberry (Aronia sp.) (low in fat) eaten stayed the same.

Another study was done by Dr. Smith using the plasma metabolic profile (blood samples). These samples provide information on metabolic fuel use and energetic condition. Lipid metabolites indicate how mass has changed over the last several hours (showing refueling). Other metabolites provide more information. Plasma was also sampled at two different stopover sites to compare them.

These sits were the Braddock Bay Bird Observatory and Rochester Institute of Technology Bird Observatory. At Bradock Bay Bird Observatory there was 200% more ripe fruit and this was 83% native berries (tend to be higher energy). At Rochester Institute of Technology, there were only 10% native berries. Birds were sampled the same day and same time at these locations. It was found that at Braddock Bay Bird Observatory those birds had higher triglyceride levels. This proves that fruit is helpful in birds refueling.

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Dr. Smith hopes to continue in researching the effects of fruit on birds. One study she wants to do is compare seasonal and site differences in fruits nutritional content. She also wants to look at if the bushes that provide fruit provide a year round value (such as a place to nest in or find insects). She wants to develop fruit fingers prints (light that comes off fruit when you shine a fluorescent light on it). This can be used to quickly tell if a fruit has high or low nutrients. Lastly, Dr. Smith wants to see if invasive species are so integrated into the system that removing then would cause harm to bird by removing a food source.

Ecosystem roles in tropical rainforests

Primary producers in all of these ecosystems vary. In rainforests, the primary producers include trees, shrubs, and epiphytes. An epiphyte is a plant that grows on another plant but it not directly parasitic. In mangroves, they are epiphyte and mangroves. The term mangrove describes how the trees live, it is not a taxonomic term. It simply describes a tree that lives in salt water. In a reef, the primary producers are corals, seagrass, and macroalgae (seaweed). Interestingly corals are also predators of the reef. The algae they are in a symbiotic relationship (zooxanthellae) with undergoes photosynthesis during the day. At night they hunt small organisms in the water and spear them with tiny barbs.

 

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A view of Guatemala primary producers. Captured by Lauren Schramm

 

Herbivores (or primary consumers) in the mangroves, rainforest, and reefs all vary. In rainforests, these include birds, monkeys, agouti, tapir, butterflies, and sloths. In the mangroves there are fewer herbivores, these include mollusks and crabs. In the reef system, most organisms are herbivores. These include coral, smaller fish, sponges, plankton, and mollusks.

 

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An Agouti (Dasyprocta punctata )

 

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Wetland delineation

The purpose of doing a wetland delineation is to establish the wetland boundary. This can be done either using the soil or the vegetation in that area. The US Army Corps of Engineers manual on Wetlands Delineation is considered the standard although there are different supplemental manuals depending the region that you are in. It is mandatory to use the manual to identify and delineate wetlands that could be subject to regulation under Section 404 of the Clean water act. While mudflats are protected under section 404, the manual only deals with vegetated sites, aka wetlands. Both the list of plants and soils listed in the manual are considered obsolete. A newer list of plants is available here and a newer list of soils is available here.

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In order to defer something as a wetland it has to meet three key criteria; saturated soils from a permanent or periodic inundation of groundwater, vegetation adapted for life in saturated soils, and the presence of “normal circumstances”. More specifically soil must be classified as hydric and the mean water depth is less than 6.6 feet deep. Wetlands may be surrounded by either deepwater aquatic habitats or nonwetlands. See the Army Corp manual on pages 10 and 11 for more specific definitions of these habitat types.

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Order Lepidoptera

The order Lepidoptera contains butterflies and moths. There are over 180,000 species in the order which is divided into 126 families and 46 superfamilies. They account for 10 percent of known species worldwide. The order is defined by the scales that cover them, wings, and a proboscis. They also undergo a complete metamorphosis between the larvae and adult stage. Some scientists have even theorized that caterpillars and adults are different species and metamorphosis changes the genes that are active. This is known as the death and resurrection theory. Butterflies and moths are important pollinators and members of the food chain. Because there are so many families in this group I have chosen to just focus on 5 families for now.

  • Saturniidae
    • this is a moth family with over 2,300 described species in it
    • adults have large bodies and wings
      • the bodies have hair like scales on them
      • wings often contain eyespots
      • front and back wings overlap
      • wingspans are typically 1-6 inches but the atlas moth (Attacus atlas) has a wingspan of 12 inches!
    • notable members include the giant silk moths, emperor moths, and royal moths
    • this family contains some agricultural pests as well as the moths that spin silk
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An atlas moth (Attacus atlas)
  • Papilionidae, or the swallowtail butterflies
    • this family has over 550 species
    • while most species are tropical these butterflies can be found on every continent but Antartica
    • the family included the largest butterflies in the world with the largest being Queen Alexandra’s birdwing (Ornithoptera alexandrae) which can have a wingspan of 9.8 inches
    • the larvae in this family have a defend organ called an osmeterium

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Jekyll Island Nature

The Georgia coast contains many unique habitats. Although the coastline is only 90 miles long it contains a third of all coastal wetlands on the East Coast. Most of these wetlands are found in the region referred to as the Golden Isles which are made up of Brunswick and its four barrier islands; St Simons Island, Jekyll Island, Sea Island and Little St Simons. These islands actually contain 28 percent of the coastal wetlands of the east coast of the united states. Jekyll Island in particular is owned by the State of Georgia, which has created zoning that allows 65 percent of the island to remain in a natural state. I have been fortunate enough to spend some time in this region and it is well worth the 4-hour drive from metro Atlanta to get there.

 

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Driftwood beach. Captured by Lauren Schramm

 

Driftwood beach on Jekyll Island is among the most well known in the region. Strong currents let to erosion which caused the trees to die, which were then preserved by the salt air. The in the southern part of the beach there are piles of large rocks. In these rocks, you can find sea squirts, blue mussels (Mytilus edulis), and some species of crabs. Be sure to visit the beach at low tide as the critters in these rocks can only be accessed at this time. In addition, as the tide rises most of the beach goes underwater and you will be forced to either walk back in the uplands or in the water. If you walk northward on the beach you can reach a bike path that runs through a salt marsh. If you continue north you will eventually end up in St Simons Sound. This marsh contains a lot of bird species, in fact, e-bird has reports of over 304 species here. If you don’t have an e-bird you can view birds that have been seen on the beach on this inaturalist page.  This is in part due to the fact that the beach serves as a critical stop-over habitat for migrating shorebirds. Highlights include the threatened birds like the piping plover (Charadrius melodus), wood stork (Mycteria americana), golden-winged warbler (Vermivora chrysoptera), red-cockaded woodpecker (Leuconotopicus borealis), black-capped petrel (Pterodroma hasitata) and Fea’s petrel (Pterodroma feae).

 

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A wood stork (Mycteria americana)

 

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Spring Peeper (Pseudacris crucifer)

The spring peeper (Pseudacris crucifer) is a small frog that produces a very loud sound that those who live on the East Coast of the United States are very familiar with. Peepers range in size from 0.5 inches to only an inch. Males call to attract females. They either sit on vegetation or in the water to call. They will defend a small territory in which they call. Those males who can peep more loudly and rapidly have an increased chance of attracting a female. Larger males also tend to breed more. Due to the energetic cost of this event, peepers are not sexually mature until they are 3 years old. Once they are mature they waste no time, and one of the 1st frog species to start reproducing after hibernation ends. Females also lay a whopping 600 to 1000 eggs per season making them an R selected species. They are in the family, Hylidae which contains a wide range of species but is generally considered to be treefrogs and their allies.

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They are a terrestrial species and prefer to live in wooded areas near water bodies that they breed in. While they are good climbers (in fact they even have tiny suction cups at the end of each finger) they prefer to live hidden in the leaf litter or on the ground. They will lay their eggs in vernal pools, ponds or wetlands. The larvae then metaphorize 45 to 90 days later depending on water availability.  The frogs have a preference for those waterbodies that have vegetation and those without fish which can be predators of their larvae.  A study in Arkansas documented that the species uses caves in the event of a drought because of the high relative humidity.

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A spring peeper (Pseudacris crucifer) on my friend’s hand. Captured by Lauren Schramm

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Passenger pigeon genetics

Unlike other species, passenger pigeons (Ectopistes migratorius) faced a recent extinction. This extinction took place at the turn of the 20th century, the last individual died in captivity in 1914. Based on morphology it was assumed that they belonged in the genus Zenaida (Fulton 2012). This genus consists of mourning doves. When the mitochondrial DNA was analyzed it was found that they are more closely related to Patagioenas which are the New World pigeons. They used mitochondrial DNA because there is a high number of copies of this DNA in the cells when you compare this to the 2 copies of DNA that are in the nucleus. For this reason, it is common to use this for the analysis of ancient DNA.

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