Habitat quality drives birds' reproductive success

Date: May 18, 2016

Source: Central Ornithology Publication Office

Five songbird species in California's oak woodlands each seek out a different habitat to maximize their reproductive success, according to new research in The Auk: Ornithological Advances.

The quality of a bird's habitat can be a crucial factor in its reproductive success, and it's an important part of managing land for sensitive species. However, it's hard to measure habitat quality directly, so biologists often turn to occupancy rates instead, reasoning that birds will tend to build their nests in better habitats. For this study, Megan Milligan and Janis Dickinson of the Cornell Lab of Ornithology focused on five species--the Ash-throated Flycatcher, House Wren, Oak Titmouse, Violet-green Swallow, and Western Bluebird--tracking their use of nest boxes in different habitat types and how successful they were.

From 1990 to 2001, researchers checked 360 nest boxes in the oak woodlands of California's Monterey County every week during the breeding season. When they classified the vegetation surrounding each box, they found that each species differed in kinds of habitat it tended to use. House Wrens, for example, preferred sites with less grassland and plenty of riparian vegetation, while Violet-green Swallows tended to favor chaparral and avoid riparian corridors. These differences could reflect preference for different habitats, or they could be a less preferred outcome of competition for the best habitat types. Occupancy was the best predictor of nest success for all five species, suggesting that box occupancy is a good indicator of habitat quality and that each species' use of habitat represents a preference, rather than exclusion from better habitats due to competition.

Continued ...

Songbird habitat affects reproduction, survival

Date: August 27, 2015

Source: The University of Montana

Summary: A professor who studies birds around the world has discovered trends in how the offspring grow, how parents care for the young and how well the young survive based on where they live.

A University of Montana professor who studies birds around the world has discovered trends in how the offspring grow, how parents care for the young and how well the young survive based on where they live. Now, his songbird research is hitting the right notes with the journal Science.

Thomas Martin, assistant leader of the U.S. Geological Survey Montana Cooperative Fish and Wildlife Research Unit at UM, set out to explain why tropical birds tend to have fewer offspring that seem to grow slower and live longer, slower lives than their northern counterparts. He found tropical songbirds grow their wings faster, aided by higher parental feeding rates for fewer offspring than temperate species. Those differences, Martin said, ultimately translate to how well the offspring escape predators both in the nest and after they leave it.

Martin's article, "Age-Related Mortality Explains Life History Strategies of Tropical and Temperate Songbirds," will be published Aug. 28 in the journal Science.

Read on ...

Desire to reproduce drives active nightlife of birds

Date: January 21, 2014

Source: University of Illinois College of Agricultural, Consumer and Environmental Sciences (ACES)

Summary: For a non-nocturnal bird, the yellow-breasted chat spends a significant amount of time visiting other birds’ territories during the night. After studying the birds’ movement, it was noted that males were active almost every night, while the females were also active at night, but particularly so during the window of time when they were fertile.

Read on

Study reveals how birds lost their penises

New research sheds light on why some birds have lost their penises over the course of evolution.

Land fowl, such as chickens, have normally developing penises as early embryos, but only have rudimentary organs as adults.

A study in Current Biology shows that these birds initiate a genetic "programme" during development that stops the budding penises from growing.

The loss of the organ could have given hens more control over reproduction.

Co-author Dr Martin Cohn, from the University of Florida in Gainesville, said: "Our discovery shows that reduction of the penis during bird evolution occurred by activation of a normal mechanism of programmed cell death in a new location, the tip of the emerging penis."

The team discovered that a gene called Bmp4 plays a critical role in this process. In chicken development, Bmp4 switches on and the birds' developing male genitals shrink away.

In ducks and emus, which retain their penises, the gene stays switched off and the organs continue to grow.

Continued

Birds studied to understand trade-offs between reproduction, immunity

University of Delaware post-doctoral researcher Ian Stewart is conducting research to answer this question a bit more scientifically. His subjects – tree swallows – make human parents look like slouches. Both the mother and father tree swallow feed their hatchlings every five minutes, 12 hours a day.  (It should be noted, though, that their parenting gig is much shorter than ours—after 17 or 18 days the young leave the nest.) Stewart is studying these small, migratory birds to better understand the trade-offs they make between reproduction and immunity. His research could potentially help scientists who study human biology better understand our own immune system and its stressors. Stewart is part of a young but growing interdisciplinary field called ecoimmunology, which combines aspects of immunology with ecology, biology, physiology and evolution. He chose to focus his research on tree swallows and bluebirds because both are fairly tolerant of human interaction. "Some birds don't like being observed but tree swallows and bluebirds don't get stressed from being watched or handled," notes Stewart.  There's another very important benefit to working with these birds—since they nest in boxes, not up in the trees, they're a heck of lot easier to catch.  Throughout the breeding season, Stewart catches the parent birds, injects them with a harmless antigen and releases them. Then, he re-catches the same birds a few days later to take blood samples and assess each bird's immune response to the antigens.  "Some of the tree swallows work harder at parenting," notes Stewart. "It may be because the bird has four hatchlings to feed instead of just three. Other times, the bird is simply more energetic at taking care of its hatchlings, regardless of brood size." 

Read more at:

 http://phys.org/news/2012-11-birds-trade-offs-reproduction-immunity.html#jCp