Understanding Annual Cycles of Birds

1. Chapter – 9: Annual Cycles of Birds Chapter 9 on the 23rd, 25th and then finish on March 4th (!). We’ll have outside lab on the 27th, and I may be out on March 2nd

2. Annual Cycles • As species living in un-conditioned outdoor habitats birds face strong seasonal variation • Day/night differences • Temperature (maximum and minimum) • Food availability • Water availability • Throughout a single calendar year birds do different things • Molting feathers, annual or alternate molt • Breeding • Migrating • Need to link costly activities to times of plenty

3. Annual Cycles Annual cycle for a Mallard (Anas platyrhynchos) but this could be for most any species

4. Annual Cycles Annual cycles can be either complex or simple (as the one shown here for the Rock Dove, Columba livia)

5. Annual Cycles Even tropical species like the Bicolored Antbird (Gymnopithys leucaspis) have seasons, driven by light and rain in most cases Annual cycles can be quite complex with many things going on through the year. Typically day length and food are important drivers of these patterns.

6. Annual Cycles • Many species are not sedentary • Breeding and non-breeding grounds separate • Adds an additional layer of complexity • Many species migrate • Some are extreme in distance • Some are short-distance

7. White-crowned Sparrows (Zonotrichicaleucophrys) have variable migration lengths • This will alter what each population will be doing on an annual basis • Some move earlier than others • Some breed later than others • Brood sizes and attempts differ

8. Annual Cycles • What drives annual cycles and changes in physiology/behavior? • Day length very important • Long days = warmer weather = good time to breed • Secondary cues important too • Leaves coming out – food and cover • Insect abundance – food for you and young • Minimum temperatures – your young can survive the night • Water – food and temperature influence, we all need water! • Secondary cues probably more important to females than males • Species, overall, vary in how important secondary cues are

9. Annual Cycles Environmental cues (primary and secondary) drive each stage, phases within stages, and help move one stage to the next

10. Annual Cycles • Primary and secondary environmental information taken in • Information turned into response • Hypothalamic-pituitary-gonadal axis (HPG axis) • Hormones of HPG axis drive behavior and physiology Human HPG axis example here, but birds have one too

11. Annual Cycles • Hypothalamus – located in brain • ‘Interpreter’ – incoming information passed into hypothalamus • Comprised of neurosecretory nerve cells • Nerve information comes in to nerve, hormone information leaves nerve cell • For seasonality, gonadotropin-releasing hormone (GnRH) very important • Long days, more GnRH produced than during short days • Beginning to breed, more GnRH produced leading to gamete maturation and release • See a member of the opposite sex – more GnRH produced • Someone ticks you off – more GnRH produced

12. Annual Cycles • GnRH released into hypophysial portal blood system • Direct shunting to the pituitary • Pituitary cells respond to GnRH by releasing their own hormones • Luteinizing hormone (LH) • Follicle-stimulating hormone (FSH) The pituitary is an encased organ that responds strongly to the hypothalamus. Together with the hypothalamus it comprises one of the most important regulatory structures in the body.

13. Annual Cycles • LH and FSH from the pituitary goes to the gonads (testes or ovary) – induce steroid hormone release • LH in particular, induced testosterone (T) production • Steroid hormones important to reproduction • Increases lead to gamete maturation • Increases lead to breeding behavior • Mate displays, receptive behavior, territoriality • Increases lead to acquisition of breeding plumages • *** Both increases in steroid hormones (and non-steroids!) and decreases in hormones can influence movements across life stages

14. Annual cycles Here Northern Cardinals, and this is beginning in December. They get a more responsive HPG axis as we move towards breeding (DeVries et al. 2011)

15. Annual Cycles Dark-eyed Junco (Junco hyemalis) Injections of GnRH ultimately stimulate T production. Shows interesting seasonal variation, but cannot tell if it’s the hypothalamus, pituitary, or gonad that becoming less responsive (Jawor et al., 2006, GCE)

16. Annual Cycles Changes in steroid hormones also influence levels of thyroid hormones. Thyroid hormones influence molt, body composition, and thermoregulation European Starling (Sturnus vulgarus)

17. Annual Cycles • Linking of seasons and breeding • Warmer temperatures may mean keeping eggs/young alive • Warmer temperatures typically mean more food • Many small birds feed their young insects • Warmer temperatures give independent young time to prepare Great Blue Heron (Ardea herodias) nest with 2 nestlings

18. Annual Cycles • Migration – must get this timed just right too • Day length, again, very important • Increasing (**) days in the spring – want to head to breeding grounds • If you’re in the southern hemisphere you’re actually seeing decreasing day lengths • Shortening days in the winter – want to leave breeding grounds • With changes in day length see increases in fat, migratory restlessness (Zugunruhe), hyperphagia • Hormone changes are a part of getting ready for migration • Also trying to get into good weather patterns for easy traveling

19. Annual Cycles • What allows birds to track time? • Must integrate physiological and behavioral changes with time of year • Pineal gland • Pineal contains photosensitive cells in birds • May be directly exposed to light • Melatonin Standard cage set up for measuring migration restlessness (Zugunruhe)

20. Annual Cycles Melatonin production occurs at night, melatonin ‘seen’ by many tissues including the hypothalamus. Gives a measure of length of night. Along with light entrains the biological clock (a Zeitgeber) and allows tracking of time passage.

21. Annual Cycles What if it’s all going horribly wrong? Stress = corticosterone and movement into ‘Emergency life history stage’ (save yourself!) What constitutes bad?

22. Annual Cycles – Non-cyclic activity! Angel Tern (Gygis alba) White-tailed tropicbird (Phaethon lepturus) Molts almost continually Breeds at irregular intervals

23. Annual Cycles • Complexities due to climate change • Temperature an important secondary signal for seasonal cycles • Migrants vs. non-migrants on common breeding grounds • Food plants have shifted distribution and flower times • Could be detrimental to species dependent on them • Breeding time changes have been recorded! • Insects do not respond to temperature changes as birds do • Earlier breeding birds may not have adequate food for young

24. Annual Cycles Common House Martins (Delichon urbicum) both arrive and leave breeding grounds earlier now, co-varies with increasing temperatures at their wintering grounds

25. Annual Cycles Tree Swallows (Tachycineta bicolor) nesting earlier each year. Co-varies with temperatures experienced in May.

26. Annual Cycles Blue Tits (Cyanistes caeruleus) on Corsica and environmental change – what can happen