Phenology in urban environments - The effects of tree and prey phenology on the reproduction of urban and rural great tits (Parus major)

Abstract

Urban environments are rapidly growing worldwide with severe consequences to animals and plants residing in our cities. Some of the most well-studied urban wildlife is passerine birds, where a wide array of effects have been documented; smaller clutches, earlier breeding, shorter telomeres and oxidative stress are just some costs among numerous others. Yet, few studies have so far investigated the altered phenology caused by urban habitats. In this study I follow three urban populations of great tits in southern Sweden and examine the effects from urban heat islands on tree and caterpillar phenology. I observed the urban heat islands effect in all cities, different tree phenology in the two largest cities, and an overall shift in larvae emergence, together with lower total invertebrate biomass. However, I found no difference in the great tits hatching dates between the urban and rural habitats. This is likely a mismatch by the urban great tits to the local food peak. Such a maladaptation could have arisen due to the urban environments low quality food sources and possible high mortality, in combination with a gene flow from adjacent rural populations.

Popular Abstract

The Hectic City-life of an Urban Bird

Do you ever feel like everything is more stressful in the city? Traffic is busy, people are running late to appointments and there is never time sit down and have a decent lunch. Well, if you feel this way you are not alone; the birds in our cities feel the same way. Being used to a country-side lifestyle, the birds are just not able to adapt to the slightly altered schedule of a city. Here, the insects they eat are not only scarcer, but also appear earlier in spring. Since the birds depend on the insects to feed their chicks, being delayed in the city’s timetable is a matter of life or death for birds.

What do you think of when you hear the word “nature”? Maybe you picture a pristine forest, dark and mysterious, or a scenic national park with wilderness spanning as far as you can see in all directions. Although this no doubt is nature, so are the trees in the city parks and the pigeons perched on lamp posts. As our urban areas keep expanding rapidly, more and more research has been done in the field of urban ecology, which focus on studying nature in cities. This new field is not only important for understanding urban wildlife, but also offers insights on how we humans can (or cannot) co-exists with nature. What researchers have found in urban birds so far is that they eat junk food, have gotten a city accent in their calls, and have become duller in colour than their country-side cousins.

In my study I wanted to learn if the urban birds have started following the schedule of the city or if they still live by the slower rural clock. I followed the great tits, a common bird in and out of cities, in the three largest cities in southern Sweden: Gothenburg, Malmö and Helsingborg. I also recorded the temperature, and studied the trees and insects at the same cities. I paid extra close attention to caterpillars, as it is the tits staple diet.

What I found was that each city was slightly warmer compared to outside of the cities. This is caused by an effect called urban heat islands, which is a well-known phenomenon related to man-made structures and heat sources increasing temperature. In the two largest cities, Malmö and Gothenburg, I found that the trees would get their first leafs over a week earlier in spring. I also found that the caterpillars that only eat leafs, and love young and crisp ones, would appear earlier in the city. Yet, the great tits in the cities seemed not to have taken notice of this and laid their eggs at the same time as their cousins out in the forest. This means that not only will parents have more trouble feeding their chicks caterpillars since insects are scarcer in cities, but as the chicks are hatched at the same time in the city as outside, and with the insects being earlier in the city, this will perhaps result in a poorer diet than they could have gotten, had they been earlier. This scenario will lead to a much harder childhood for the tits, and likely much fewer of the chicks would it to adulthood, compared to outside cities.
So why don’t the birds just adapt their laying date to the phenology of the insects? With such dire consequences it is perhaps strange that the birds have not adapted to their new home. One potential explanation may lie in the rate birds are moving into the cities. The resident city birds have a hard time due to many reasons, but mainly a lack of insects could makes few birds survive to breeding age. Yet every year, new hopeful provincial birds may move into the city. This might create a situation with rural migrants being the majority of the birds in the city and since evolution acts over generations, no progress in adaption can be made. This a bit of speculation to the cause, but a conclusion we can draw is that birds might not be ready for all aspects of the urban life style our cities force upon them.

Degree Project in Biology 30 credits 2017

Advisors: Caroline Isaksson and Hannah Watson
Department of Biology, Lund University

• author: Kjellberg Jensen, Johan
• supervisor: Caroline Isaksson; Hannah Watson
• organization: Degree Projects in Biology
• course: BIOY01 20171
• year: 2017
• type: M2 - Bachelor Degree
• subject: Biology and Life Sciences
• language: English
• id: 8925057
• date added to LUP: 2017-09-08 13:39:18
• date last changed: 2017-09-08 13:39:18